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+ PostgreSQL için Sıkça Sorulan Sorular (SSS) Son güncelleme : 19 Mayıs
+ 2003 Pazartesi - 03:05:21 Current maintainer: Bruce Momjian
+ (pgman@candle.pha.pa.us ) Çeviren : Devrim GÜNDÜZ (devrim@gunduz.org )
+ Nicolai Tufar (ntufar@yahoo.com ) Bu belgenin en güncel hali,
+ http://www.PostgreSQL.org/docs/faqs/FAQ_turkish.html ve
+ http://www.gunduz.org/seminer/pg/FAQ_turkish adreslerinde görülebilir.
+ Platforma özel sorularınız,http://www.PostgreSQL.org/docs/index.html
+ adresinde yanıtlanır..
+ ----------------------------------------------------------------------
+ -- Genel Sorular 1.1 <#1.1>) PostgreSQL nedir? Nasıl okunur? 1.2
+ <#1.2>) PostgreSQL' in hakları nedir? 1.3 <#1.3>) PostgreSQL, hangi
+ Unix platformlarında çalısır? 1.4 <#1.4>) Hangi Unix olmayan
+ uyarlamaları bulunmaktadır? 1.5 <#1.5>) PostgreSQL'i nereden
+ indirebilirim? 1.6 <#1.6>) Desteği nereden alabilirim? 1.7 <#1.7>) En
+ son sürümü nedir? 1.8 <#1.8>) Hangi belgelere ulasabilirim? 1.9
+ <#1.9>) Bilinen hatalar ya da eksik özelliklere nereden ulasabilirim?
+ 1.10 <#1.10>) Nasıl SQL öğrenebilirim? 1.11 <#1.11>) PostgreSQL 2000
+ yılına uyumlu mudur? 1.12 <#1.12>) Geliştirme takımına nasıl
+ katılabilirim?? 1.13 <#1.13>) Bir hata raporunu nasıl gönderebilirim?
+ 1.14 <#1.14>) PostgreSQL, diger VTYS(DBMS lerle nasıl
+ karşılaştırılabilir? 1.15 <#1.15>) PostgreSQL'e maddi açıdan nasıl
+ destek olabilirim? Kullanıcı/istemci Soruları 2.1 <#2.1>) Are there
+ ODBC drivers for PostgreSQL? 2.2 <#2.2>) What tools are available for
+ using PostgreSQL with Web pages? 2.3 <#2.3>) Does PostgreSQL have a
+ graphical user interface? 2.4 <#2.4>) What languages are available to
+ communicate with PostgreSQL? Administrative Questions 3.1 <#3.1>) How
+ do I install PostgreSQL somewhere other than //usr/local/pgsql/? 3.2
+ <#3.2>) When I start /postmaster/, I get a /Bad System Call/ or core
+ dumped message. Why? 3.3 <#3.3>) When I try to start /postmaster/, I
+ get /IpcMemoryCreate/ errors. Why? 3.4 <#3.4>) When I try to start
+ /postmaster/, I get /IpcSemaphoreCreate/ errors. Why? 3.5 <#3.5>) How
+ do I control connections from other hosts? 3.6 <#3.6>) How do I tune
+ the database engine for better performance? 3.7 <#3.7>) What debugging
+ features are available? 3.8 <#3.8>) Why do I get /"Sorry, too many
+ clients"/ when trying to connect? 3.9 <#3.9>) What is in the
+ /pgsql_tmp/ directory? 3.10 <#3.10>) Why do I need to do a dump and
+ restore to upgrade PostgreSQL releases? Operational Questions 4.1
+ <#4.1>) What is the difference between binary cursors and normal
+ cursors? 4.2 <#4.2>) How do I SELECT only the first few rows of a
+ query? 4.3 <#4.3>) How do I get a list of tables or other things I can
+ see in /psql/? 4.4 <#4.4>) How do you remove a column from a table?
+ 4.5 <#4.5>) What is the maximum size for a row, a table, and a
+ database? 4.6 <#4.6>) How much database disk space is required to
+ store data from a typical text file? 4.7 <#4.7>) How do I find out
+ what tables, indexes, databases, and users are defined? 4.8 <#4.8>) My
+ queries are slow or don't make use of the indexes. Why? 4.9 <#4.9>)
+ How do I see how the query optimizer is evaluating my query? 4.10
+ <#4.10>) What is an R-tree index? 4.11 <#4.11>) What is the Genetic
+ Query Optimizer? 4.12 <#4.12>) How do I perform regular expression
+ searches and case-insensitive regular expression searches? How do I
+ use an index for case-insensitive searches? 4.13 <#4.13>) In a query,
+ how do I detect if a field is NULL? 4.14 <#4.14>) What is the
+ difference between the various character types? 4.15.1 <#4.15.1>) How
+ do I create a serial/auto-incrementing field? 4.15.2 <#4.15.2>) How do
+ I get the value of a SERIAL insert? 4.15.3 <#4.15.3>) Don't
+ /currval()/ and /nextval()/ lead to a race condition with other users?
+ 4.15.4 <#4.15.4>) Why aren't my sequence numbers reused on transaction
+ abort? Why are there gaps in the numbering of my sequence/SERIAL
+ column? 4.16 <#4.16>) What is an OID? What is a TID? 4.17 <#4.17>)
+ What is the meaning of some of the terms used in PostgreSQL? 4.18
+ <#4.18>) Why do I get the error /"ERROR: Memory exhausted in
+ AllocSetAlloc()"/? 4.19 <#4.19>) How do I tell what PostgreSQL version
+ I am running? 4.20 <#4.20>) Why does my large-object operations get
+ /"invalid large obj descriptor"/? 4.21 <#4.21>) How do I create a
+ column that will default to the current time? 4.22 <#4.22>) Why are my
+ subqueries using |IN| so slow? 4.23 <#4.23>) How do I perform an outer
+ join? 4.24 <#4.24>) How do I perform queries using multiple databases?
+ 4.25 <#4.25>) How do I return multiple rows or columns from a
+ function? 4.26 <#4.26>) Why can't I reliably create/drop temporary
+ tables in PL/PgSQL functions? 4.27 <#4.27>) What replication options
+ are available? 4.28 <#4.28>) What encryption options are available?
+ Extending PostgreSQL 5.1 <#5.1>) I wrote a user-defined function. When
+ I run it in /psql/, why does it dump core? 5.2 <#5.2>) How can I
+ contribute some nifty new types and functions to PostgreSQL? 5.3
+ <#5.3>) How do I write a C function to return a tuple? 5.4 <#5.4>) I
+ have changed a source file. Why does the recompile not see the change?
+ ----------------------------------------------------------------------
+ -- General Questions 1.1) What is PostgreSQL? How is it pronounced?
+ PostgreSQL is pronounced /Post-Gres-Q-L/. PostgreSQL is an enhancement
+ of the POSTGRES database management system, a next-generation DBMS
+ research prototype. While PostgreSQL retains the powerful data model
+ and rich data types of POSTGRES, it replaces the PostQuel query
+ language with an extended subset of SQL. PostgreSQL is free and the
+ complete source is available. PostgreSQL development is performed by a
+ team of developers who all subscribe to the PostgreSQL development
+ mailing list. The current coordinator is Marc G. Fournier
+ (scrappy@PostgreSQL.org ). (See section 1.6 <#1.6> on how to join).
+ This team is now responsible for all development of PostgreSQL. The
+ authors of PostgreSQL 1.01 were Andrew Yu and Jolly Chen. Many others
+ have contributed to the porting, testing, debugging, and enhancement
+ of the code. The original Postgres code, from which PostgreSQL is
+ derived, was the effort of many graduate students, undergraduate
+ students, and staff programmers working under the direction of
+ Professor Michael Stonebraker at the University of California,
+ Berkeley. The original name of the software at Berkeley was Postgres.
+ When SQL functionality was added in 1995, its name was changed to
+ Postgres95. The name was changed at the end of 1996 to PostgreSQL.
+ 1.2) What is the copyright on PostgreSQL? PostgreSQL is subject to the
+ following COPYRIGHT: PostgreSQL Data Base Management System Portions
+ copyright (c) 1996-2002, PostgreSQL Global Development Group Portions
+ Copyright (c) 1994-6 Regents of the University of California
+ Permission to use, copy, modify, and distribute this software and its
+ documentation for any purpose, without fee, and without a written
+ agreement is hereby granted, provided that the above copyright notice
+ and this paragraph and the following two paragraphs appear in all
+ copies. IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO
+ ANY PARTY FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL
+ DAMAGES, INCLUDING LOST PROFITS, ARISING OUT OF THE USE OF THIS
+ SOFTWARE AND ITS DOCUMENTATION, EVEN IF THE UNIVERSITY OF CALIFORNIA
+ HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. THE UNIVERSITY OF
+ CALIFORNIA SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING, BUT NOT
+ LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS ON AN "AS IS"
+ BASIS, AND THE UNIVERSITY OF CALIFORNIA HAS NO OBLIGATIONS TO PROVIDE
+ MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS. The
+ above is the BSD license, the classic open-source license. It has no
+ restrictions on how the source code may be used. We like it and have
+ no intention of changing it. 1.3) What Unix platforms does PostgreSQL
+ run on? In general, a modern Unix-compatible platform should be able
+ to run PostgreSQL. The platforms that had received explicit testing at
+ the time of release are listed in the installation instructions. 1.4)
+ What non-Unix ports are available? *Client* It is possible to compile
+ the /libpq/ C library, psql, and other interfaces and client
+ applications to run on MS Windows platforms. In this case, the client
+ is running on MS Windows, and communicates via TCP/IP to a server
+ running on one of our supported Unix platforms. A file /win32.mak/ is
+ included in the distribution for making a Win32 /libpq/ library and
+ /psql/. PostgreSQL also communicates with ODBC clients. *Server* The
+ database server can run on Windows NT and Win2k using Cygwin, the
+ Cygnus Unix/NT porting library. See /pgsql/doc/FAQ_MSWIN/ in the
+ distribution or the MS Windows FAQ at
+ http://www.PostgreSQL.org/docs/faqs/text/FAQ_MSWIN
+ www.PostgreSQL.org/docs/faqs/text/FAQ_MSWIN>. A native port to MS Win
+ NT/2000/XP is currently being worked on. For more details on the
+ current status of PostgreSQL on Windows see
+ http://techdocs.postgresql.org/guides/Windows
+ techdocs.postgresql.org/guides/Windows>. There is also a Novell
+ Netware 6 port at http://forge.novell.com. 1.5) Where can I get
+ PostgreSQL? The primary anonymous ftp site for PostgreSQL is
+ ftp://ftp.PostgreSQL.org/pub. For mirror sites, see our main web site.
+ 1.6) Where can I get support? The main mailing list is:
+ pgsql-general@PostgreSQL.org . It is available for discussion of
+ matters pertaining to PostgreSQL. To subscribe, send mail with the
+ following lines in the body (not the subject line): subscribe end to
+ pgsql-general-request@PostgreSQL.org . There is also a digest list
+ available. To subscribe to this list, send email to:
+ pgsql-general-digest-request@PostgreSQL.org with a body of: subscribe
+ end Digests are sent out to members of this list whenever the main
+ list has received around 30k of messages. The bugs mailing list is
+ available. To subscribe to this list, send email to
+ pgsql-bugs-request@PostgreSQL.org with a body of: subscribe end There
+ is also a developers discussion mailing list available. To subscribe
+ to this list, send email to pgsql-hackers-request@PostgreSQL.org with
+ a body of: subscribe end Additional mailing lists and information
+ about PostgreSQL can be found via the PostgreSQL WWW home page at:
+ http://www.PostgreSQL.org There is also an IRC channel on EFNet and
+ OpenProjects, channel /#PostgreSQL/. I use the Unix command |irc -c
+ '#PostgreSQL' "$USER" irc.phoenix.net.| A list of commercial support
+ companies is available at
+ http://www.ca.PostgreSQL.org/users-lounge/commercial-support.html.
+ 1.7) What is the latest release? The latest release of PostgreSQL is
+ version 7.3.3. We plan to have major releases every four months. 1.8)
+ What documentation is available? Several manuals, manual pages, and
+ some small test examples are included in the distribution. See the
+ //doc/ directory. You can also browse the manuals online at
+ http://www.PostgreSQL.org/docs. There are two PostgreSQL books
+ available online at http://www.PostgreSQL.org/docs/awbook.html and
+ http://www.commandprompt.com/ppbook/. There is a list of PostgreSQL
+ books available for purchase at http://www.ca.PostgreSQL.org/books/.
+ There is also a collection of PostgreSQL technical articles at
+ http://techdocs.PostgreSQL.org/. /psql/ has some nice \d commands to
+ show information about types, operators, functions, aggregates, etc.
+ Our web site contains even more documentation. 1.9) How do I find out
+ about known bugs or missing features? PostgreSQL supports an extended
+ subset of SQL-92. See our TODO developer.PostgreSQL.org/todo.php> list
+ for known bugs, missing features, and future plans. 1.10) How can I
+ learn SQL? The PostgreSQL book at
+ http://www.PostgreSQL.org/docs/awbook.html teaches SQL. There is
+ another PostgreSQL book at http://www.commandprompt.com/ppbook.
+ www.commandprompt.com/ppbook/> There is a nice tutorial at
+ http://www.intermedia.net/support/sql/sqltut.shtm,
+ www.intermedia.net/support/sql/sqltut.shtm> at
+ http://ourworld.compuserve.com/homepages/graeme_birchall/HTM_COOK.HTM,
+ ourworld.compuserve.com/homepages/graeme_birchall/HTM_COOK.HTM> and at
+ http://sqlcourse.com. sqlcourse.com/> Another one is "Teach Yourself
+ SQL in 21 Days, Second Edition" at
+ http://members.tripod.com/er4ebus/sql/index.htm Many of our users like
+ /The Practical SQL Handbook/, Bowman, Judith S., et al.,
+ Addison-Wesley. Others like /The Complete Reference SQL/, Groff et
+ al., McGraw-Hill. 1.11) Is PostgreSQL Y2K compliant? Yes, we easily
+ handle dates past the year 2000 AD, and before 2000 BC. 1.12) How do I
+ join the development team? First, download the latest source and read
+ the PostgreSQL Developers documentation on our web site, or in the
+ distribution. Second, subscribe to the /pgsql-hackers/ and
+ /pgsql-patches/ mailing lists. Third, submit high quality patches to
+ pgsql-patches. There are about a dozen people who have commit
+ privileges to the PostgreSQL CVS archive. They each have submitted so
+ many high-quality patches that it was impossible for the existing
+ committers to keep up, and we had confidence that patches they
+ committed were of high quality. 1.13) How do I submit a bug report?
+ Please visit the PostgreSQL BugTool page at
+ http://www.PostgreSQL.org/bugs/bugs.php, which gives guidelines and
+ directions on how to submit a bug report. Also check out our ftp site
+ ftp://ftp.PostgreSQL.org/pub to see if there is a more recent
+ PostgreSQL version or patches. 1.14) How does PostgreSQL compare to
+ other DBMSs? There are several ways of measuring software: features,
+ performance, reliability, support, and price. *Features* PostgreSQL
+ has most features present in large commercial DBMSs, like
+ transactions, subselects, triggers, views, foreign key referential
+ integrity, and sophisticated locking. We have some features they do
+ not have, like user-defined types, inheritance, rules, and
+ multi-version concurrency control to reduce lock contention.
+ *Performance* PostgreSQL has performance similar to other commercial
+ and open source databases. it is faster for some things, slower for
+ others. In comparison to MySQL or leaner database systems, we are
+ slower on inserts/updates because of transaction overhead. Of course,
+ MySQL does not have any of the features mentioned in the /Features/
+ section above. We are built for reliability and features, though we
+ continue to improve performance in every release. There is an
+ interesting Web page comparing PostgreSQL to MySQL at
+ http://openacs.org/philosophy/why-not-mysql.html
+ openacs.org/philosophy/why-not-mysql.html> *Reliability* We realize
+ that a DBMS must be reliable, or it is worthless. We strive to release
+ well-tested, stable code that has a minimum of bugs. Each release has
+ at least one month of beta testing, and our release history shows that
+ we can provide stable, solid releases that are ready for production
+ use. We believe we compare favorably to other database software in
+ this area. *Support* Our mailing lists provide contact with a large
+ group of developers and users to help resolve any problems
+ encountered. While we cannot guarantee a fix, commercial DBMSs do not
+ always supply a fix either. Direct access to developers, the user
+ community, manuals, and the source code often make PostgreSQL support
+ superior to other DBMSs. There is commercial per-incident support
+ available for those who need it. (See FAQ section 1.6 <#1.6>.) *Price*
+ We are free for all use, both commercial and non-commercial. You can
+ add our code to your product with no limitations, except those
+ outlined in our BSD-style license stated above. 1.15) How can I
+ financially assist PostgreSQL? PostgreSQL has had a first-class
+ infrastructure since we started in 1996. This is all thanks to Marc
+ Fournier, who has created and managed this infrastructure over the
+ years. Quality infrastructure is very important to an open-source
+ project. It prevents disruptions that can greatly delay forward
+ movement of the project. Of course, this infrastructure is not cheap.
+ There are a variety of monthly and one-time expenses that are required
+ to keep it going. If you or your company has money it can donate to
+ help fund this effort, please go to http://store.pgsql.com/shopping/
+ and make a donation. Although the web page mentions PostgreSQL, Inc,
+ the "contributions" item is solely to support the PostgreSQL project
+ and does not fund any specific company. If you prefer, you can also
+ send a check to the contact address.
+ ----------------------------------------------------------------------
+ -- User Client Questions 2.1) Are there ODBC drivers for PostgreSQL?
+ There are two ODBC drivers available, PsqlODBC and OpenLink ODBC. You
+ can download PsqlODBC from
+ http://gborg.postgresql.org/project/psqlodbc/projdisplay.php
+ gborg.postgresql.org/project/psqlodbc/projdisplay.php>. OpenLink ODBC
+ can be gotten from http://www.openlinksw.com www.openlinksw.com/>. It
+ works with their standard ODBC client software so you'll have
+ PostgreSQL ODBC available on every client platform they support (Win,
+ Mac, Unix, VMS). They will probably be selling this product to people
+ who need commercial-quality support, but a freeware version will
+ always be available. Please send questions to
+ postgres95@openlink.co.uk . 2.2) What tools are available for using
+ PostgreSQL with Web pages? A nice introduction to Database-backed Web
+ pages can be seen at: http://www.webreview.com For Web integration,
+ PHP is an excellent interface. It is at http://www.php.net. For
+ complex cases, many use the Perl interface and CGI.pm or mod_perl.
+ 2.3) Does PostgreSQL have a graphical user interface? Yes, there are
+ several graphical interfaces to PostgreSQL available. These include
+ PgAccess http://www.pgaccess.org www.pgaccess.org>), PgAdmin II
+ (http://www.pgadmin.org, Win32-only), RHDB Admin
+ (http://sources.redhat.com/rhdb/ ) and Rekall (
+ http://www.thekompany.com/products/rekall/
+ www.thekompany.com/products/rekall/>, proprietary). There is also
+ PHPPgAdmin ( http://phppgadmin.sourceforge.net/
+ phppgadmin.sourceforge.net/>), a web-based interface to PostgreSQL.
+ See http://techdocs.postgresql.org/guides/GUITools for a more detailed
+ list. 2.4) What languages are able to communicate with PostgreSQL?
+ Most popular programming languages contain an interface to PostgreSQL.
+ Check your programming language's list of extension modules. The
+ following interfaces are included in the PostgreSQL distribution: * C
+ (libpq) * Embedded C (ecpg) * Java (jdbc) * Python (PyGreSQL) * TCL
+ (libpgtcl) Additional interfaces are available at
+ http://gborg.postgresql.org in the /Drivers/Interfaces/ section.
+ ----------------------------------------------------------------------
+ -- Administrative Questions 3.1) How do I install PostgreSQL somewhere
+ other than //usr/local/pgsql/? Specify the /--prefix/ option when
+ running /configure/. 3.2) When I start /postmaster/, I get a /Bad
+ System Call/ or core dumped message. Why? It could be a variety of
+ problems, but first check to see that you have System V extensions
+ installed in your kernel. PostgreSQL requires kernel support for
+ shared memory and semaphores. 3.3) When I try to start /postmaster/, I
+ get /IpcMemoryCreate/ errors. Why? You either do not have shared
+ memory configured properly in your kernel or you need to enlarge the
+ shared memory available in the kernel. The exact amount you need
+ depends on your architecture and how many buffers and backend
+ processes you configure for /postmaster/. For most systems, with
+ default numbers of buffers and processes, you need a minimum of ~1 MB.
+ See the PostgreSQL Administrator's Guide
+ www.PostgreSQL.org/docs/view.php?version=current&idoc=1&file=kernel-re
+ sources.html> for more detailed information about shared memory and
+ semaphores. 3.4) When I try to start /postmaster/, I get
+ /IpcSemaphoreCreate/ errors. Why? If the error message is
+ /IpcSemaphoreCreate: semget failed (No space left on device)/ then
+ your kernel is not configured with enough semaphores. Postgres needs
+ one semaphore per potential backend process. A temporary solution is
+ to start /postmaster/ with a smaller limit on the number of backend
+ processes. Use /-N/ with a parameter less than the default of 32. A
+ more permanent solution is to increase your kernel's SEMMNS and SEMMNI
+ parameters. Inoperative semaphores can also cause crashes during heavy
+ database access. If the error message is something else, you might not
+ have semaphore support configured in your kernel at all. See the
+ PostgreSQL Administrator's Guide for more detailed information about
+ shared memory and semaphores. 3.5) How do I control connections from
+ other hosts? By default, PostgreSQL only allows connections from the
+ local machine using Unix domain sockets. Other machines will not be
+ able to connect unless you add the /-i/ flag to /postmaster/, *and*
+ enable host-based authentication by modifying the file
+ /$PGDATA/pg_hba.conf/ accordingly. This will allow TCP/IP connections.
+ 3.6) How do I tune the database engine for better performance?
+ Certainly, indexes can speed up queries. The EXPLAIN command allows
+ you to see how PostgreSQL is interpreting your query, and which
+ indexes are being used. If you are doing many INSERTs, consider doing
+ them in a large batch using the COPY command. This is much faster than
+ individual INSERTS. Second, statements not in a BEGIN WORK/COMMIT
+ transaction block are considered to be in their own transaction.
+ Consider performing several statements in a single transaction block.
+ This reduces the transaction overhead. Also, consider dropping and
+ recreating indexes when making large data changes. There are several
+ tuning options. You can disable /fsync()/ by starting /postmaster/
+ with a /-o -F/ option. This will prevent /fsync()/s from flushing to
+ disk after every transaction. You can also use the /postmaster/ /-B/
+ option to increase the number of shared memory buffers used by the
+ backend processes. If you make this parameter too high, the
+ /postmaster/ may not start because you have exceeded your kernel's
+ limit on shared memory space. Each buffer is 8K and the default is 64
+ buffers. You can also use the backend /-S/ option to increase the
+ maximum amount of memory used by the backend process for temporary
+ sorts. The /-S/ value is measured in kilobytes, and the default is 512
+ (i.e. 512K). You can also use the CLUSTER command to group data in
+ tables to match an index. See the CLUSTER manual page for more
+ details. 3.7) What debugging features are available? PostgreSQL has
+ several features that report status information that can be valuable
+ for debugging purposes. First, by running /configure/ with the
+ --enable-cassert option, many /assert()/s monitor the progress of the
+ backend and halt the program when something unexpected occurs. Both
+ /postmaster/ and /postgres/ have several debug options available.
+ First, whenever you start /postmaster/, make sure you send the
+ standard output and error to a log file, like: cd /usr/local/pgsql
+ ./bin/postmaster >server.log 2>&1 & This will put a server.log file in
+ the top-level PostgreSQL directory. This file contains useful
+ information about problems or errors encountered by the server.
+ /Postmaster/ has a /-d/ option that allows even more detailed
+ information to be reported. The /-d/ option takes a number that
+ specifies the debug level. Be warned that high debug level values
+ generate large log files. If /postmaster/ is not running, you can
+ actually run the /postgres/ backend from the command line, and type
+ your SQL statement directly. This is recommended *only* for debugging
+ purposes. Note that a newline terminates the query, not a semicolon.
+ If you have compiled with debugging symbols, you can use a debugger to
+ see what is happening. Because the backend was not started from
+ /postmaster/, it is not running in an identical environment and
+ locking/backend interaction problems may not be duplicated. If
+ /postmaster/ is running, start /psql/ in one window, then find the PID
+ of the /postgres/ process used by /psql/. Use a debugger to attach to
+ the /postgres/ PID. You can set breakpoints in the debugger and issue
+ queries from /psql/. If you are debugging /postgres/ startup, you can
+ set PGOPTIONS="-W n", then start /psql/. This will cause startup to
+ delay for /n/ seconds so you can attach to the process with the
+ debugger, set any breakpoints, and continue through the startup
+ sequence. The /postgres/ program has /-s, -A/, and /-t/ options that
+ can be very useful for debugging and performance measurements. You can
+ also compile with profiling to see what functions are taking execution
+ time. The backend profile files will be deposited in the
+ /pgsql/data/base/dbname/ directory. The client profile file will be
+ put in the client's current directory. Linux requires a compile with
+ /-DLINUX_PROFILE/ for proper profiling. 3.8) Why do I get /"Sorry, too
+ many clients"/ when trying to connect? You need to increase
+ /postmaster/'s limit on how many concurrent backend processes it can
+ start. The default limit is 32 processes. You can increase it by
+ restarting /postmaster/ with a suitable /-N/ value or modifying
+ /postgresql.conf/. Note that if you make /-N/ larger than 32, you must
+ also increase /-B/ beyond its default of 64; /-B/ must be at least
+ twice /-N/, and probably should be more than that for best
+ performance. For large numbers of backend processes, you are also
+ likely to find that you need to increase various Unix kernel
+ configuration parameters. Things to check include the maximum size of
+ shared memory blocks, SHMMAX; the maximum number of semaphores, SEMMNS
+ and SEMMNI; the maximum number of processes, NPROC; the maximum number
+ of processes per user, MAXUPRC; and the maximum number of open files,
+ NFILE and NINODE. The reason that PostgreSQL has a limit on the number
+ of allowed backend processes is so your system won't run out of
+ resources. 3.9) What is in the /pgsql_tmp/ directory? This directory
+ contains temporary files generated by the query executor. For example,
+ if a sort needs to be done to satisfy an ORDER BY and the sort
+ requires more space than the backend's /-S/ parameter allows, then
+ temporary files are created here to hold the extra data. The temporary
+ files are usually deleted automatically, but might remain if a backend
+ crashes during a sort. A stop and restart of the /postmaster/ will
+ remove files from those directories. 3.10) Why do I need to do a dump
+ and restore to upgrade between major PostgreSQL releases? The
+ PostgreSQL team makes only small changes between minor releases, so
+ upgrading from 7.2 to 7.2.1 does not require a dump and restore.
+ However, major releases (e.g. from 7.2 to 7.3) often change the
+ internal format of system tables and data files. These changes are
+ often complex, so we don't maintain backward compatability for data
+ files. A dump outputs data in a generic format that can then be loaded
+ in using the new internal format. In releases where the on-disk format
+ does not change, the /pg_upgrade/ script can be used to upgrade
+ without a dump/restore. The release notes mention whether /pg_upgrade/
+ is available for the release.
+ ----------------------------------------------------------------------
+ -- Operational Questions 4.1) What is the difference between binary
+ cursors and normal cursors? See the DECLARE manual page for a
+ description. 4.2) How do I SELECT only the first few rows of a query?
+ See the FETCH manual page, or use SELECT ... LIMIT.... The entire
+ query may have to be evaluated, even if you only want the first few
+ rows. Consider using a query that has an ORDER BY. If there is an
+ index that matches the ORDER BY, PostgreSQL may be able to evaluate
+ only the first few records requested, or the entire query may have to
+ be evaluated until the desired rows have been generated. 4.3) How do I
+ get a list of tables or other things I can see in /psql/? You can read
+ the source code for /psql/ in file /pgsql/src/bin/psql/describe.c/. It
+ contains SQL commands that generate the output for psql's backslash
+ commands. You can also start /psql/ with the /-E/ option so it will
+ print out the queries it uses to execute the commands you give. 4.4)
+ How do you remove a column from a table? This functionality was added
+ in release 7.3 with ALTER TABLE DROP COLUMN. In earlier versions, you
+ can do this: BEGIN; LOCK TABLE old_table; SELECT ... -- select all
+ columns but the one you want to remove INTO TABLE new_table FROM
+ old_table; DROP TABLE old_table; ALTER TABLE new_table RENAME TO
+ old_table; COMMIT; 4.5) What is the maximum size for a row, a table,
+ and a database? These are the limits: Maximum size for a database?
+ unlimited (4 TB databases exist) Maximum size for a table? 16 TB
+ Maximum size for a row? 1.6TB Maximum size for a field? 1 GB Maximum
+ number of rows in a table? unlimited Maximum number of columns in a
+ table? 250-1600 depending on column types Maximum number of indexes on
+ a table? unlimited Of course, these are not actually unlimited, but
+ limited to available disk space and memory/swap space. Performance may
+ suffer when these values get unusually large. The maximum table size
+ of 16 TB does not require large file support from the operating
+ system. Large tables are stored as multiple 1 GB files so file system
+ size limits are not important. The maximum table size and maximum
+ number of columns can be increased if the default block size is
+ increased to 32k. 4.6) How much database disk space is required to
+ store data from a typical text file? A PostgreSQL database may require
+ up to five times the disk space to store data from a text file. As an
+ example, consider a file of 100,000 lines with an integer and text
+ description on each line. Suppose the text string avergages twenty
+ bytes in length. The flat file would be 2.8 MB. The size of the
+ PostgreSQL database file containing this data can be estimated as 6.4
+ MB: 36 bytes: each row header (approximate) 24 bytes: one int field
+ and one text field + 4 bytes: pointer on page to tuple
+ ---------------------------------------- 64 bytes per row The data
+ page size in PostgreSQL is 8192 bytes (8 KB), so: 8192 bytes per page
+ ------------------- = 128 rows per database page (rounded down) 64
+ bytes per row 100000 data rows -------------------- = 782 database
+ pages (rounded up) 128 rows per page 782 database pages * 8192 bytes
+ per page = 6,406,144 bytes (6.4 MB) Indexes do not require as much
+ overhead, but do contain the data that is being indexed, so they can
+ be large also. NULLs are stored in bitmaps, so they use very little
+ space. 4.7) How do I find out what tables, indexes, databases, and
+ users are defined? /psql/ has a variety of backslash commands to show
+ such information. Use \? to see them. There are also system tables
+ beginning with /pg_/ that describe these too. Also, /psql -l/ will
+ list all databases. Also try the file
+ /pgsql/src/tutorial/syscat.source/. It illustrates many of the SELECTs
+ needed to get information from the database system tables. 4.8) My
+ queries are slow or don't make use of the indexes. Why? Indexes are
+ not automatically used by every query. Indexes are only used if the
+ table is larger than a minimum size, and the query selects only a
+ small percentage of the rows in the table. This is because the random
+ disk access caused by an index scan can be slower than a straight read
+ through the table, or sequential scan. To determine if an index should
+ be used, PostgreSQL must have statistics about the table. These
+ statistics are collected using VACUUM ANALYZE, or simply ANALYZE.
+ Using statistics, the optimizer knows how many rows are in the table,
+ and can better determine if indexes should be used. Statistics are
+ also valuable in determining optimal join order and join methods.
+ Statistics collection should be performed periodically as the contents
+ of the table change. Indexes are normally not used for ORDER BY or to
+ perform joins. A sequential scan followed by an explicit sort is
+ usually faster than an index scan of a large table. However, LIMIT
+ combined with ORDER BY often will use an index because only a small
+ portion of the table is returned. In fact, though MAX() and MIN()
+ don't use indexes, it is possible to retrieve such values using an
+ index with ORDER BY and LIMIT: SELECT col FROM tab ORDER BY col [ DESC
+ ] LIMIT 1; If you believe the optimizer is incorrect in choosing a
+ sequential scan, use |SET enable_seqscan TO 'off'| and run tests to
+ see if an index scan is indeed faster. When using wild-card operators
+ such as LIKE or /~/, indexes can only be used in certain
+ circumstances: * The beginning of the search string must be anchored
+ to the start of the string, i.e. o LIKE patterns must not start with
+ /%/. o /~/ (regular expression) patterns must start with /^/. * The
+ search string can not start with a character class, e.g. [a-e]. *
+ Case-insensitive searches such as ILIKE and /~*/ do not utilise
+ indexes. Instead, use functional indexes, which are described in
+ section 4.12 <#4.12>. * The default /C/ locale must be used during
+ /initdb/. 4.9) How do I see how the query optimizer is evaluating my
+ query? See the EXPLAIN manual page. 4.10) What is an R-tree index? An
+ R-tree index is used for indexing spatial data. A hash index can't
+ handle range searches. A B-tree index only handles range searches in a
+ single dimension. R-trees can handle multi-dimensional data. For
+ example, if an R-tree index can be built on an attribute of type
+ /point/, the system can more efficiently answer queries such as
+ "select all points within a bounding rectangle." The canonical paper
+ that describes the original R-tree design is: Guttman, A. "R-trees: A
+ Dynamic Index Structure for Spatial Searching." Proceedings of the
+ 1984 ACM SIGMOD Int'l Conf on Mgmt of Data, 45-57. You can also find
+ this paper in Stonebraker's "Readings in Database Systems". Built-in
+ R-trees can handle polygons and boxes. In theory, R-trees can be
+ extended to handle higher number of dimensions. In practice, extending
+ R-trees requires a bit of work and we don't currently have any
+ documentation on how to do it. 4.11) What is the Genetic Query
+ Optimizer? The GEQO module speeds query optimization when joining many
+ tables by means of a Genetic Algorithm (GA). It allows the handling of
+ large join queries through nonexhaustive search. 4.12) How do I
+ perform regular expression searches and case-insensitive regular
+ expression searches? How do I use an index for case-insensitive
+ searches? The /~/ operator does regular expression matching, and /~*/
+ does case-insensitive regular expression matching. The
+ case-insensitive variant of LIKE is called ILIKE. Case-insensitive
+ equality comparisons are normally expressed as: SELECT * FROM tab
+ WHERE lower(col) = 'abc'; This will not use an standard index.
+ However, if you create a functional index, it will be used: CREATE
+ INDEX tabindex ON tab (lower(col)); 4.13) In a query, how do I detect
+ if a field is NULL? You test the column with IS NULL and IS NOT NULL.
+ 4.14) What is the difference between the various character types? Type
+ Internal Name Notes --------------------------------------------------
+ VARCHAR(n) varchar size specifies maximum length, no padding CHAR(n)
+ bpchar blank padded to the specified fixed length TEXT text no
+ specific upper limit on length BYTEA bytea variable-length byte array
+ (null-byte safe) "char" char one character You will see the internal
+ name when examining system catalogs and in some error messages. The
+ first four types above are "varlena" types (i.e., the first four bytes
+ on disk are the length, followed by the data). Thus the actual space
+ used is slightly greater than the declared size. However, these data
+ types are also subject to compression or being stored out-of-line by
+ TOAST, so the space on disk might also be less than expected.
+ VARCHAR(n) is best when storing variable-length strings and it limits
+ how long a string can be. TEXT is for strings of unlimited length,
+ with a maximum of one gigabyte. CHAR(n) is for storing strings that
+ are all the same length. CHAR(n) pads with blanks to the specified
+ length, while VARCHAR(n) only stores the characters supplied. BYTEA is
+ for storing binary data, particularly values that include NULL bytes.
+ All the types described here have similar performance characteristics.
+ 4.15.1) How do I create a serial/auto-incrementing field? PostgreSQL
+ supports a SERIAL data type. It auto-creates a sequence and index on
+ the column. For example, this: CREATE TABLE person ( id SERIAL, name
+ TEXT ); is automatically translated into this: CREATE SEQUENCE
+ person_id_seq; CREATE TABLE person ( id INT4 NOT NULL DEFAULT
+ nextval('person_id_seq'), name TEXT ); CREATE UNIQUE INDEX
+ person_id_key ON person ( id ); See the /create_sequence/ manual page
+ for more information about sequences. You can also use each row's
+ /OID/ field as a unique value. However, if you need to dump and reload
+ the database, you need to use /pg_dump/'s /-o/ option or COPY WITH
+ OIDS option to preserve the OIDs. 4.15.2) How do I get the value of a
+ SERIAL insert? One approach is to retrieve the next SERIAL value from
+ the sequence object with the /nextval()/ function /before/ inserting
+ and then insert it explicitly. Using the example table in 4.15.1
+ <#4.15.1>, an example in a pseudo-language would look like this:
+ new_id = execute("SELECT nextval('person_id_seq')"); execute("INSERT
+ INTO person (id, name) VALUES (new_id, 'Blaise Pascal')"); You would
+ then also have the new value stored in |new_id| for use in other
+ queries (e.g., as a foreign key to the |person| table). Note that the
+ name of the automatically created SEQUENCE object will be named
+ __/seq/, where /table/ and /serialcolumn/ are the names of your table
+ and your SERIAL column, respectively. Alternatively, you could
+ retrieve the assigned SERIAL value with the /currval()/ function
+ /after/ it was inserted by default, e.g., execute("INSERT INTO person
+ (name) VALUES ('Blaise Pascal')"); new_id = execute("SELECT
+ currval('person_id_seq')"); Finally, you could use the OID <#4.16>
+ returned from the INSERT statement to look up the default value,
+ though this is probably the least portable approach. In Perl, using
+ DBI with Edmund Mergl's DBD::Pg module, the oid value is made
+ available via /$sth->{pg_oid_status}/ after /$sth->execute()/. 4.15.3)
+ Don't /currval()/ and /nextval()/ lead to a race condition with other
+ users? No. /currval()/ returns the current value assigned by your
+ backend, not by all users. 4.15.4) Why aren't my sequence numbers
+ reused on transaction abort? Why are there gaps in the numbering of my
+ sequence/SERIAL column? To improve concurrency, sequence values are
+ given out to running transactions as needed and are not locked until
+ the transaction completes. This causes gaps in numbering from aborted
+ transactions. 4.16) What is an OID? What is a TID? OIDs are
+ PostgreSQL's answer to unique row ids. Every row that is created in
+ PostgreSQL gets a unique OID. All OIDs generated during /initdb/ are
+ less than 16384 (from /include/access/transam.h/). All user-created
+ OIDs are equal to or greater than this. By default, all these OIDs are
+ unique not only within a table or database, but unique within the
+ entire PostgreSQL installation. PostgreSQL uses OIDs in its internal
+ system tables to link rows between tables. These OIDs can be used to
+ identify specific user rows and used in joins. It is recommended you
+ use column type OID to store OID values. You can create an index on
+ the OID field for faster access. OIDs are assigned to all new rows
+ from a central area that is used by all databases. If you want to
+ change the OID to something else, or if you want to make a copy of the
+ table, with the original OIDs, there is no reason you can't do it:
+ CREATE TABLE new_table(old_oid oid, mycol int); SELECT old_oid, mycol
+ INTO new FROM old; COPY new TO '/tmp/pgtable'; DELETE FROM new; COPY
+ new WITH OIDS FROM '/tmp/pgtable'; OIDs are stored as 4-byte integers,
+ and will overflow at 4 billion. No one has reported this ever
+ happening, and we plan to have the limit removed before anyone does.
+ TIDs are used to identify specific physical rows with block and offset
+ values. TIDs change after rows are modified or reloaded. They are used
+ by index entries to point to physical rows. 4.17) What is the meaning
+ of some of the terms used in PostgreSQL? Some of the source code and
+ older documentation use terms that have more common usage. Here are
+ some: * table, relation, class * row, record, tuple * column, field,
+ attribute * retrieve, select * replace, update * append, insert * OID,
+ serial value * portal, cursor * range variable, table name, table
+ alias A list of general database terms can be found at:
+ http://hea-www.harvard.edu/MST/simul/software/docs/pkgs/pgsql/glossary
+ /glossary.html 4.18) Why do I get the error /"ERROR: Memory exhausted
+ in AllocSetAlloc()"/? You probably have run out of virtual memory on
+ your system, or your kernel has a low limit for certain resources. Try
+ this before starting /postmaster/: ulimit -d 262144 limit datasize
+ 256m Depending on your shell, only one of these may succeed, but it
+ will set your process data segment limit much higher and perhaps allow
+ the query to complete. This command applies to the current process,
+ and all subprocesses created after the command is run. If you are
+ having a problem with the SQL client because the backend is returning
+ too much data, try it before starting the client. 4.19) How do I tell
+ what PostgreSQL version I am running? From /psql/, type |SELECT
+ version();| 4.20) Why does my large-object operations get /"invalid
+ large obj descriptor"/? You need to put |BEGIN WORK| and |COMMIT|
+ around any use of a large object handle, that is, surrounding
+ |lo_open| ... |lo_close.| Currently PostgreSQL enforces the rule by
+ closing large object handles at transaction commit. So the first
+ attempt to do anything with the handle will draw /invalid large obj
+ descriptor/. So code that used to work (at least most of the time)
+ will now generate that error message if you fail to use a transaction.
+ If you are using a client interface like ODBC you may need to set
+ |auto-commit off.| 4.21) How do I create a column that will default to
+ the current time? Use /CURRENT_TIMESTAMP/: |CREATE TABLE test (x int,
+ modtime timestamp DEFAULT CURRENT_TIMESTAMP ); | 4.22) Why are my
+ subqueries using |IN| so slow? Currently, we join subqueries to outer
+ queries by sequentially scanning the result of the subquery for each
+ row of the outer query. If the subquery returns only a few rows and
+ the outer query returns many rows, |IN| is fastest. To speed up other
+ queries, replace |IN| with |EXISTS|: SELECT * FROM tab WHERE col IN
+ (SELECT subcol FROM subtab); to: SELECT * FROM tab WHERE EXISTS
+ (SELECT subcol FROM subtab WHERE subcol = col); For this to be fast,
+ |subcol| should be an indexed column. This preformance problem will be
+ fixed in 7.4. 4.23) How do I perform an outer join? PostgreSQL
+ supports outer joins using the SQL standard syntax. Here are two
+ examples: SELECT * FROM t1 LEFT OUTER JOIN t2 ON (t1.col = t2.col); or
+ SELECT * FROM t1 LEFT OUTER JOIN t2 USING (col); These identical
+ queries join t1.col to t2.col, and also return any unjoined rows in t1
+ (those with no match in t2). A RIGHT join would add unjoined rows of
+ t2. A FULL join would return the matched rows plus all unjoined rows
+ from t1 and t2. The word OUTER is optional and is assumed in LEFT,
+ RIGHT, and FULL joins. Ordinary joins are called INNER joins. In
+ previous releases, outer joins can be simulated using UNION and NOT
+ IN. For example, when joining /tab1/ and /tab2/, the following query
+ does an /outer/ join of the two tables: SELECT tab1.col1, tab2.col2
+ FROM tab1, tab2 WHERE tab1.col1 = tab2.col1 UNION ALL SELECT
+ tab1.col1, NULL FROM tab1 WHERE tab1.col1 NOT IN (SELECT tab2.col1
+ FROM tab2) ORDER BY col1 4.24) How do I perform queries using multiple
+ databases? There is no way to query a database other than the current
+ one. Because PostgreSQL loads database-specific system catalogs, it is
+ uncertain how a cross-database query should even behave.
+ /contrib/dblink/ allows cross-database queries using function calls.
+ Of course, a client can make simultaneous connections to different
+ databases and merge the results on the client side. 4.25) How do I
+ return multiple rows or columns from a function? In 7.3, you can
+ easily return multiple rows or columns from a function,
+ http://techdocs.postgresql.org/guides/SetReturningFunctions
+ techdocs.postgresql.org/guides/SetReturningFunctions>. 4.26) Why can't
+ I reliably create/drop temporary tables in PL/PgSQL functions?
+ PL/PgSQL caches function contents, and an unfortunate side effect is
+ that if a PL/PgSQL function accesses a temporary table, and that table
+ is later dropped and recreated, and the function called again, the
+ function will fail because the cached function contents still point to
+ the old temporary table. The solution is to use EXECUTE for temporary
+ table access in PL/PgSQL. This will cause the query to be reparsed
+ every time. 4.27) What replication options are available? There are
+ several master/slave replication options available. These allow only
+ the master to make database changes and the slave can only do database
+ reads. The bottom of
+ http://gborg.PostgreSQL.org/genpage?replication_research
+ gborg.PostgreSQL.org/genpage?replication_research> lists them. A
+ multi-master replication solution is being worked on at
+ http://gborg.PostgreSQL.org/project/pgreplication/projdisplay.php.
+ 4.28) What encryption options are available? * /contrib/pgcrypto/
+ contains many encryption functions for use in SQL queries. * The only
+ way to encrypt transmission from the client to the server is by using
+ /hostssl/ in /pg_hba.conf/. * Database user passwords are
+ automatically encrypted when stored in version 7.3. In previous
+ versions, you must enable the option /PASSWORD_ENCRYPTION/ in
+ /postgresql.conf/. * The server can run using an encrypted file
+ system.
+ ----------------------------------------------------------------------
+ -- Extending PostgreSQL 5.1) I wrote a user-defined function. When I
+ run it in /psql/, why does it dump core? The problem could be a number
+ of things. Try testing your user-defined function in a stand-alone
+ test program first. 5.2) How can I contribute some nifty new types and
+ functions to PostgreSQL? Send your extensions to the /pgsql-hackers/
+ mailing list, and they will eventually end up in the /contrib//
+ subdirectory. 5.3) How do I write a C function to return a tuple? In
+ versions of PostgreSQL beginning with 7.3, table-returning functions
+ are fully supported in C, PL/PgSQL, and SQL. See the Programmer's
+ Guide for more information. An example of a table-returning function
+ defined in C can be found in /contrib/tablefunc/. 5.4) I have changed
+ a source file. Why does the recompile not see the change? The
+ /Makefiles/ do not have the proper dependencies for include files. You
+ have to do a /make clean/ and then another /make/. If you are using
+ GCC you can use the /--enable-depend/ option of /configure/ to have
+ the compiler compute the dependencies automatically.
diff --git a/doc/src/FAQ/FAQ_turkish.html b/doc/src/FAQ/FAQ_turkish.html
new file mode 100644
index 0000000000000000000000000000000000000000..38944666bb86299c4add24e28d1c9b45bc7a9af5
--- /dev/null
+++ b/doc/src/FAQ/FAQ_turkish.html
@@ -0,0 +1,1255 @@
+
+ PostgreSQL için Sıkça Sorulan Sorular (SSS)
+
+Son güncelleme : 19 Mayıs 2003 Pazartesi - 03:05:21
+
+Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us
+<mailto:pgman@candle.pha.pa.us>)
+
+Çeviren : Devrim GÜNDÜZ (devrim@gunduz.org <mailto:devrim@gunduz.org>)
+Nicolai Tufar (ntufar@yahoo.com <mailto:ntufar@yahoo.com>)
+
+Bu belgenin en güncel hali,
+http://www.PostgreSQL.org/docs/faqs/FAQ_turkish.html ve
+http://www.gunduz.org/seminer/pg/FAQ_turkish adreslerinde görülebilir.
+
+Platforma özel sorularınız,http://www.PostgreSQL.org/docs/index.html
+adresinde yanıtlanır..
+
+------------------------------------------------------------------------
+
+
+ Genel Sorular
+
+1.1 <#1.1>) PostgreSQL nedir? Nasıl okunur?
+1.2 <#1.2>) PostgreSQL' in hakları nedir?
+1.3 <#1.3>) PostgreSQL, hangi Unix platformlarında çalısır?
+1.4 <#1.4>) Hangi Unix olmayan uyarlamaları bulunmaktadır?
+1.5 <#1.5>) PostgreSQL'i nereden indirebilirim?
+1.6 <#1.6>) Desteği nereden alabilirim?
+1.7 <#1.7>) En son sürümü nedir?
+1.8 <#1.8>) Hangi belgelere ulasabilirim?
+1.9 <#1.9>) Bilinen hatalar ya da eksik özelliklere nereden ulasabilirim?
+1.10 <#1.10>) Nasıl SQL öğrenebilirim?
+1.11 <#1.11>) PostgreSQL 2000 yılına uyumlu mudur?
+1.12 <#1.12>) Geliştirme takımına nasıl katılabilirim??
+1.13 <#1.13>) Bir hata raporunu nasıl gönderebilirim?
+1.14 <#1.14>) PostgreSQL, diger VTYS(DBMS lerle nasıl karşılaştırılabilir?
+1.15 <#1.15>) PostgreSQL'e maddi açıdan nasıl destek olabilirim?
+
+
+ Kullanıcı/istemci Soruları
+
+2.1 <#2.1>) Are there ODBC drivers for PostgreSQL?
+2.2 <#2.2>) What tools are available for using PostgreSQL with Web pages?
+2.3 <#2.3>) Does PostgreSQL have a graphical user interface?
+2.4 <#2.4>) What languages are available to communicate with PostgreSQL?
+
+
+ Administrative Questions
+
+3.1 <#3.1>) How do I install PostgreSQL somewhere other than
+//usr/local/pgsql/?
+3.2 <#3.2>) When I start /postmaster/, I get a /Bad System Call/ or core
+dumped message. Why?
+3.3 <#3.3>) When I try to start /postmaster/, I get /IpcMemoryCreate/
+errors. Why?
+3.4 <#3.4>) When I try to start /postmaster/, I get /IpcSemaphoreCreate/
+errors. Why?
+3.5 <#3.5>) How do I control connections from other hosts?
+3.6 <#3.6>) How do I tune the database engine for better performance?
+3.7 <#3.7>) What debugging features are available?
+3.8 <#3.8>) Why do I get /"Sorry, too many clients"/ when trying to connect?
+3.9 <#3.9>) What is in the /pgsql_tmp/ directory?
+3.10 <#3.10>) Why do I need to do a dump and restore to upgrade
+PostgreSQL releases?
+
+
+ Operational Questions
+
+4.1 <#4.1>) What is the difference between binary cursors and normal
+cursors?
+4.2 <#4.2>) How do I SELECT only the first few rows of a query?
+4.3 <#4.3>) How do I get a list of tables or other things I can see in
+/psql/?
+4.4 <#4.4>) How do you remove a column from a table?
+4.5 <#4.5>) What is the maximum size for a row, a table, and a database?
+4.6 <#4.6>) How much database disk space is required to store data from
+a typical text file?
+4.7 <#4.7>) How do I find out what tables, indexes, databases, and users
+are defined?
+4.8 <#4.8>) My queries are slow or don't make use of the indexes. Why?
+4.9 <#4.9>) How do I see how the query optimizer is evaluating my query?
+4.10 <#4.10>) What is an R-tree index?
+4.11 <#4.11>) What is the Genetic Query Optimizer?
+4.12 <#4.12>) How do I perform regular expression searches and
+case-insensitive regular expression searches? How do I use an index for
+case-insensitive searches?
+4.13 <#4.13>) In a query, how do I detect if a field is NULL?
+4.14 <#4.14>) What is the difference between the various character types?
+4.15.1 <#4.15.1>) How do I create a serial/auto-incrementing field?
+4.15.2 <#4.15.2>) How do I get the value of a SERIAL insert?
+4.15.3 <#4.15.3>) Don't /currval()/ and /nextval()/ lead to a race
+condition with other users?
+4.15.4 <#4.15.4>) Why aren't my sequence numbers reused on transaction
+abort? Why are there gaps in the numbering of my sequence/SERIAL column?
+4.16 <#4.16>) What is an OID? What is a TID?
+4.17 <#4.17>) What is the meaning of some of the terms used in PostgreSQL?
+4.18 <#4.18>) Why do I get the error /"ERROR: Memory exhausted in
+AllocSetAlloc()"/?
+4.19 <#4.19>) How do I tell what PostgreSQL version I am running?
+4.20 <#4.20>) Why does my large-object operations get /"invalid large
+obj descriptor"/?
+4.21 <#4.21>) How do I create a column that will default to the current
+time?
+4.22 <#4.22>) Why are my subqueries using |IN| so slow?
+4.23 <#4.23>) How do I perform an outer join?
+4.24 <#4.24>) How do I perform queries using multiple databases?
+4.25 <#4.25>) How do I return multiple rows or columns from a function?
+4.26 <#4.26>) Why can't I reliably create/drop temporary tables in
+PL/PgSQL functions?
+4.27 <#4.27>) What replication options are available?
+4.28 <#4.28>) What encryption options are available?
+
+
+ Extending PostgreSQL
+
+5.1 <#5.1>) I wrote a user-defined function. When I run it in /psql/,
+why does it dump core?
+5.2 <#5.2>) How can I contribute some nifty new types and functions to
+PostgreSQL?
+5.3 <#5.3>) How do I write a C function to return a tuple?
+5.4 <#5.4>) I have changed a source file. Why does the recompile not see
+the change?
+------------------------------------------------------------------------
+
+
+ General Questions
+
+
+ 1.1) What is PostgreSQL? How is it pronounced?
+
+PostgreSQL is pronounced /Post-Gres-Q-L/.
+
+PostgreSQL is an enhancement of the POSTGRES database management system,
+a next-generation DBMS research prototype. While PostgreSQL retains the
+powerful data model and rich data types of POSTGRES, it replaces the
+PostQuel query language with an extended subset of SQL. PostgreSQL is
+free and the complete source is available.
+
+PostgreSQL development is performed by a team of developers who all
+subscribe to the PostgreSQL development mailing list. The current
+coordinator is Marc G. Fournier (scrappy@PostgreSQL.org
+<mailto:scrappy@PostgreSQL.org>). (See section 1.6 <#1.6> on how to
+join). This team is now responsible for all development of PostgreSQL.
+
+The authors of PostgreSQL 1.01 were Andrew Yu and Jolly Chen. Many
+others have contributed to the porting, testing, debugging, and
+enhancement of the code. The original Postgres code, from which
+PostgreSQL is derived, was the effort of many graduate students,
+undergraduate students, and staff programmers working under the
+direction of Professor Michael Stonebraker at the University of
+California, Berkeley.
+
+The original name of the software at Berkeley was Postgres. When SQL
+functionality was added in 1995, its name was changed to Postgres95. The
+name was changed at the end of 1996 to PostgreSQL.
+
+
+ 1.2) What is the copyright on PostgreSQL?
+
+PostgreSQL is subject to the following COPYRIGHT:
+
+PostgreSQL Data Base Management System
+
+Portions copyright (c) 1996-2002, PostgreSQL Global Development Group
+Portions Copyright (c) 1994-6 Regents of the University of California
+
+Permission to use, copy, modify, and distribute this software and its
+documentation for any purpose, without fee, and without a written
+agreement is hereby granted, provided that the above copyright notice
+and this paragraph and the following two paragraphs appear in all copies.
+
+IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO ANY PARTY
+FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES,
+INCLUDING LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS
+DOCUMENTATION, EVEN IF THE UNIVERSITY OF CALIFORNIA HAS BEEN ADVISED OF
+THE POSSIBILITY OF SUCH DAMAGE.
+
+THE UNIVERSITY OF CALIFORNIA SPECIFICALLY DISCLAIMS ANY WARRANTIES,
+INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
+AND FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS
+ON AN "AS IS" BASIS, AND THE UNIVERSITY OF CALIFORNIA HAS NO OBLIGATIONS
+TO PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
+
+The above is the BSD license, the classic open-source license. It has no
+restrictions on how the source code may be used. We like it and have no
+intention of changing it.
+
+
+ 1.3) What Unix platforms does PostgreSQL run on?
+
+In general, a modern Unix-compatible platform should be able to run
+PostgreSQL. The platforms that had received explicit testing at the time
+of release are listed in the installation instructions.
+
+
+ 1.4) What non-Unix ports are available?
+
+*Client*
+
+It is possible to compile the /libpq/ C library, psql, and other
+interfaces and client applications to run on MS Windows platforms. In
+this case, the client is running on MS Windows, and communicates via
+TCP/IP to a server running on one of our supported Unix platforms. A
+file /win32.mak/ is included in the distribution for making a Win32
+/libpq/ library and /psql/. PostgreSQL also communicates with ODBC clients.
+
+*Server*
+
+The database server can run on Windows NT and Win2k using Cygwin, the
+Cygnus Unix/NT porting library. See /pgsql/doc/FAQ_MSWIN/ in the
+distribution or the MS Windows FAQ at
+http://www.PostgreSQL.org/docs/faqs/text/FAQ_MSWIN
+<http://www.PostgreSQL.org/docs/faqs/text/FAQ_MSWIN>.
+
+A native port to MS Win NT/2000/XP is currently being worked on. For
+more details on the current status of PostgreSQL on Windows see
+http://techdocs.postgresql.org/guides/Windows
+<http://techdocs.postgresql.org/guides/Windows>.
+
+There is also a Novell Netware 6 port at http://forge.novell.com.
+
+
+ 1.5) Where can I get PostgreSQL?
+
+The primary anonymous ftp site for PostgreSQL is
+ftp://ftp.PostgreSQL.org/pub. For mirror sites, see our main web site.
+
+
+ 1.6) Where can I get support?
+
+The main mailing list is: pgsql-general@PostgreSQL.org
+<mailto:pgsql-general@PostgreSQL.org>. It is available for discussion of
+matters pertaining to PostgreSQL. To subscribe, send mail with the
+following lines in the body (not the subject line):
+
+ subscribe
+ end
+
+to pgsql-general-request@PostgreSQL.org
+<mailto:pgsql-general-request@PostgreSQL.org>.
+
+There is also a digest list available. To subscribe to this list, send
+email to: pgsql-general-digest-request@PostgreSQL.org
+<mailto:pgsql-general-digest-request@PostgreSQL.org> with a body of:
+
+ subscribe
+ end
+
+Digests are sent out to members of this list whenever the main list has
+received around 30k of messages.
+
+The bugs mailing list is available. To subscribe to this list, send
+email to pgsql-bugs-request@PostgreSQL.org
+<mailto:pgsql-bugs-request@PostgreSQL.org> with a body of:
+
+ subscribe
+ end
+
+There is also a developers discussion mailing list available. To
+subscribe to this list, send email to
+pgsql-hackers-request@PostgreSQL.org
+<mailto:pgsql-hackers-request@PostgreSQL.org> with a body of:
+
+ subscribe
+ end
+
+Additional mailing lists and information about PostgreSQL can be found
+via the PostgreSQL WWW home page at:
+
+ http://www.PostgreSQL.org
+
+There is also an IRC channel on EFNet and OpenProjects, channel
+/#PostgreSQL/. I use the Unix command |irc -c '#PostgreSQL' "$USER"
+irc.phoenix.net.|
+
+A list of commercial support companies is available at
+http://www.ca.PostgreSQL.org/users-lounge/commercial-support.html.
+
+
+ 1.7) What is the latest release?
+
+The latest release of PostgreSQL is version 7.3.3.
+
+We plan to have major releases every four months.
+
+
+ 1.8) What documentation is available?
+
+Several manuals, manual pages, and some small test examples are included
+in the distribution. See the //doc/ directory. You can also browse the
+manuals online at http://www.PostgreSQL.org/docs.
+
+There are two PostgreSQL books available online at
+http://www.PostgreSQL.org/docs/awbook.html and
+http://www.commandprompt.com/ppbook/. There is a list of PostgreSQL
+books available for purchase at http://www.ca.PostgreSQL.org/books/.
+There is also a collection of PostgreSQL technical articles at
+http://techdocs.PostgreSQL.org/.
+
+/psql/ has some nice \d commands to show information about types,
+operators, functions, aggregates, etc.
+
+Our web site contains even more documentation.
+
+
+ 1.9) How do I find out about known bugs or missing features?
+
+PostgreSQL supports an extended subset of SQL-92. See our TODO
+<http://developer.PostgreSQL.org/todo.php> list for known bugs, missing
+features, and future plans.
+
+
+ 1.10) How can I learn SQL?
+
+The PostgreSQL book at http://www.PostgreSQL.org/docs/awbook.html
+teaches SQL. There is another PostgreSQL book at
+http://www.commandprompt.com/ppbook.
+<http://www.commandprompt.com/ppbook/> There is a nice tutorial at
+http://www.intermedia.net/support/sql/sqltut.shtm,
+<http://www.intermedia.net/support/sql/sqltut.shtm> at
+http://ourworld.compuserve.com/homepages/graeme_birchall/HTM_COOK.HTM,
+<http://ourworld.compuserve.com/homepages/graeme_birchall/HTM_COOK.HTM>
+and at http://sqlcourse.com. <http://sqlcourse.com/>
+
+Another one is "Teach Yourself SQL in 21 Days, Second Edition" at
+http://members.tripod.com/er4ebus/sql/index.htm
+
+Many of our users like /The Practical SQL Handbook/, Bowman, Judith S.,
+et al., Addison-Wesley. Others like /The Complete Reference SQL/, Groff
+et al., McGraw-Hill.
+
+
+ 1.11) Is PostgreSQL Y2K compliant?
+
+Yes, we easily handle dates past the year 2000 AD, and before 2000 BC.
+
+
+ 1.12) How do I join the development team?
+
+First, download the latest source and read the PostgreSQL Developers
+documentation on our web site, or in the distribution. Second, subscribe
+to the /pgsql-hackers/ and /pgsql-patches/ mailing lists. Third, submit
+high quality patches to pgsql-patches.
+
+There are about a dozen people who have commit privileges to the
+PostgreSQL CVS archive. They each have submitted so many high-quality
+patches that it was impossible for the existing committers to keep up,
+and we had confidence that patches they committed were of high quality.
+
+
+ 1.13) How do I submit a bug report?
+
+Please visit the PostgreSQL BugTool page at
+http://www.PostgreSQL.org/bugs/bugs.php, which gives guidelines and
+directions on how to submit a bug report.
+
+Also check out our ftp site ftp://ftp.PostgreSQL.org/pub to see if there
+is a more recent PostgreSQL version or patches.
+
+
+ 1.14) How does PostgreSQL compare to other DBMSs?
+
+There are several ways of measuring software: features, performance,
+reliability, support, and price.
+
+*Features*
+ PostgreSQL has most features present in large commercial DBMSs, like
+ transactions, subselects, triggers, views, foreign key referential
+ integrity, and sophisticated locking. We have some features they do
+ not have, like user-defined types, inheritance, rules, and
+ multi-version concurrency control to reduce lock contention.
+
+*Performance*
+ PostgreSQL has performance similar to other commercial and open
+ source databases. it is faster for some things, slower for others.
+ In comparison to MySQL or leaner database systems, we are slower on
+ inserts/updates because of transaction overhead. Of course, MySQL
+ does not have any of the features mentioned in the /Features/
+ section above. We are built for reliability and features, though we
+ continue to improve performance in every release. There is an
+ interesting Web page comparing PostgreSQL to MySQL at
+ http://openacs.org/philosophy/why-not-mysql.html
+ <http://openacs.org/philosophy/why-not-mysql.html>
+
+*Reliability*
+ We realize that a DBMS must be reliable, or it is worthless. We
+ strive to release well-tested, stable code that has a minimum of
+ bugs. Each release has at least one month of beta testing, and our
+ release history shows that we can provide stable, solid releases
+ that are ready for production use. We believe we compare favorably
+ to other database software in this area.
+
+*Support*
+ Our mailing lists provide contact with a large group of developers
+ and users to help resolve any problems encountered. While we cannot
+ guarantee a fix, commercial DBMSs do not always supply a fix either.
+ Direct access to developers, the user community, manuals, and the
+ source code often make PostgreSQL support superior to other DBMSs.
+ There is commercial per-incident support available for those who
+ need it. (See FAQ section 1.6 <#1.6>.)
+
+*Price*
+ We are free for all use, both commercial and non-commercial. You can
+ add our code to your product with no limitations, except those
+ outlined in our BSD-style license stated above.
+
+
+ 1.15) How can I financially assist PostgreSQL?
+
+PostgreSQL has had a first-class infrastructure since we started in
+1996. This is all thanks to Marc Fournier, who has created and managed
+this infrastructure over the years.
+
+Quality infrastructure is very important to an open-source project. It
+prevents disruptions that can greatly delay forward movement of the project.
+
+Of course, this infrastructure is not cheap. There are a variety of
+monthly and one-time expenses that are required to keep it going. If you
+or your company has money it can donate to help fund this effort, please
+go to http://store.pgsql.com/shopping/ and make a donation.
+
+Although the web page mentions PostgreSQL, Inc, the "contributions" item
+is solely to support the PostgreSQL project and does not fund any
+specific company. If you prefer, you can also send a check to the
+contact address.
+
+------------------------------------------------------------------------
+
+
+ User Client Questions
+
+
+ 2.1) Are there ODBC drivers for PostgreSQL?
+
+There are two ODBC drivers available, PsqlODBC and OpenLink ODBC.
+
+You can download PsqlODBC from
+http://gborg.postgresql.org/project/psqlodbc/projdisplay.php
+<http://gborg.postgresql.org/project/psqlodbc/projdisplay.php>.
+
+OpenLink ODBC can be gotten from http://www.openlinksw.com
+<http://www.openlinksw.com/>. It works with their standard ODBC client
+software so you'll have PostgreSQL ODBC available on every client
+platform they support (Win, Mac, Unix, VMS).
+
+They will probably be selling this product to people who need
+commercial-quality support, but a freeware version will always be
+available. Please send questions to postgres95@openlink.co.uk
+<mailto:postgres95@openlink.co.uk>.
+
+
+ 2.2) What tools are available for using PostgreSQL with Web pages?
+
+A nice introduction to Database-backed Web pages can be seen at:
+http://www.webreview.com
+
+For Web integration, PHP is an excellent interface. It is at
+http://www.php.net.
+
+For complex cases, many use the Perl interface and CGI.pm or mod_perl.
+
+
+ 2.3) Does PostgreSQL have a graphical user interface?
+
+Yes, there are several graphical interfaces to PostgreSQL available.
+These include PgAccess http://www.pgaccess.org
+<http://www.pgaccess.org>), PgAdmin II (http://www.pgadmin.org,
+Win32-only), RHDB Admin (http://sources.redhat.com/rhdb/ ) and Rekall (
+http://www.thekompany.com/products/rekall/
+<http://www.thekompany.com/products/rekall/>, proprietary). There is
+also PHPPgAdmin ( http://phppgadmin.sourceforge.net/
+<http://phppgadmin.sourceforge.net/>), a web-based interface to PostgreSQL.
+
+See http://techdocs.postgresql.org/guides/GUITools for a more detailed list.
+
+
+ 2.4) What languages are able to communicate with PostgreSQL?
+
+Most popular programming languages contain an interface to PostgreSQL.
+Check your programming language's list of extension modules.
+
+The following interfaces are included in the PostgreSQL distribution:
+
+ * C (libpq)
+ * Embedded C (ecpg)
+ * Java (jdbc)
+ * Python (PyGreSQL)
+ * TCL (libpgtcl)
+
+Additional interfaces are available at http://gborg.postgresql.org in
+the /Drivers/Interfaces/ section.
+
+------------------------------------------------------------------------
+
+
+ Administrative Questions
+
+
+ 3.1) How do I install PostgreSQL somewhere other than
+ //usr/local/pgsql/?
+
+Specify the /--prefix/ option when running /configure/.
+
+
+ 3.2) When I start /postmaster/, I get a /Bad System Call/ or
+ core dumped message. Why?
+
+It could be a variety of problems, but first check to see that you have
+System V extensions installed in your kernel. PostgreSQL requires kernel
+support for shared memory and semaphores.
+
+
+ 3.3) When I try to start /postmaster/, I get /IpcMemoryCreate/
+ errors. Why?
+
+You either do not have shared memory configured properly in your kernel
+or you need to enlarge the shared memory available in the kernel. The
+exact amount you need depends on your architecture and how many buffers
+and backend processes you configure for /postmaster/. For most systems,
+with default numbers of buffers and processes, you need a minimum of ~1
+MB. See the PostgreSQL Administrator's Guide
+<http://www.PostgreSQL.org/docs/view.php?version=current&idoc=1&file=kernel-resources.html>
+for more detailed information about shared memory and semaphores.
+
+
+ 3.4) When I try to start /postmaster/, I get
+ /IpcSemaphoreCreate/ errors. Why?
+
+If the error message is /IpcSemaphoreCreate: semget failed (No space
+left on device)/ then your kernel is not configured with enough
+semaphores. Postgres needs one semaphore per potential backend process.
+A temporary solution is to start /postmaster/ with a smaller limit on
+the number of backend processes. Use /-N/ with a parameter less than the
+default of 32. A more permanent solution is to increase your kernel's
+SEMMNS and SEMMNI parameters.
+
+Inoperative semaphores can also cause crashes during heavy database access.
+
+If the error message is something else, you might not have semaphore
+support configured in your kernel at all. See the PostgreSQL
+Administrator's Guide for more detailed information about shared memory
+and semaphores.
+
+
+ 3.5) How do I control connections from other hosts?
+
+By default, PostgreSQL only allows connections from the local machine
+using Unix domain sockets. Other machines will not be able to connect
+unless you add the /-i/ flag to /postmaster/, *and* enable host-based
+authentication by modifying the file /$PGDATA/pg_hba.conf/ accordingly.
+This will allow TCP/IP connections.
+
+
+ 3.6) How do I tune the database engine for better performance?
+
+Certainly, indexes can speed up queries. The EXPLAIN command allows you
+to see how PostgreSQL is interpreting your query, and which indexes are
+being used.
+
+If you are doing many INSERTs, consider doing them in a large batch
+using the COPY command. This is much faster than individual INSERTS.
+Second, statements not in a BEGIN WORK/COMMIT transaction block are
+considered to be in their own transaction. Consider performing several
+statements in a single transaction block. This reduces the transaction
+overhead. Also, consider dropping and recreating indexes when making
+large data changes.
+
+There are several tuning options. You can disable /fsync()/ by starting
+/postmaster/ with a /-o -F/ option. This will prevent /fsync()/s from
+flushing to disk after every transaction.
+
+You can also use the /postmaster/ /-B/ option to increase the number of
+shared memory buffers used by the backend processes. If you make this
+parameter too high, the /postmaster/ may not start because you have
+exceeded your kernel's limit on shared memory space. Each buffer is 8K
+and the default is 64 buffers.
+
+You can also use the backend /-S/ option to increase the maximum amount
+of memory used by the backend process for temporary sorts. The /-S/
+value is measured in kilobytes, and the default is 512 (i.e. 512K).
+
+You can also use the CLUSTER command to group data in tables to match an
+index. See the CLUSTER manual page for more details.
+
+
+ 3.7) What debugging features are available?
+
+PostgreSQL has several features that report status information that can
+be valuable for debugging purposes.
+
+First, by running /configure/ with the --enable-cassert option, many
+/assert()/s monitor the progress of the backend and halt the program
+when something unexpected occurs.
+
+Both /postmaster/ and /postgres/ have several debug options available.
+First, whenever you start /postmaster/, make sure you send the standard
+output and error to a log file, like:
+
+ cd /usr/local/pgsql
+ ./bin/postmaster >server.log 2>&1 &
+
+This will put a server.log file in the top-level PostgreSQL directory.
+This file contains useful information about problems or errors
+encountered by the server. /Postmaster/ has a /-d/ option that allows
+even more detailed information to be reported. The /-d/ option takes a
+number that specifies the debug level. Be warned that high debug level
+values generate large log files.
+
+If /postmaster/ is not running, you can actually run the /postgres/
+backend from the command line, and type your SQL statement directly.
+This is recommended *only* for debugging purposes. Note that a newline
+terminates the query, not a semicolon. If you have compiled with
+debugging symbols, you can use a debugger to see what is happening.
+Because the backend was not started from /postmaster/, it is not running
+in an identical environment and locking/backend interaction problems may
+not be duplicated.
+
+If /postmaster/ is running, start /psql/ in one window, then find the
+PID of the /postgres/ process used by /psql/. Use a debugger to attach
+to the /postgres/ PID. You can set breakpoints in the debugger and issue
+queries from /psql/. If you are debugging /postgres/ startup, you can
+set PGOPTIONS="-W n", then start /psql/. This will cause startup to
+delay for /n/ seconds so you can attach to the process with the
+debugger, set any breakpoints, and continue through the startup sequence.
+
+The /postgres/ program has /-s, -A/, and /-t/ options that can be very
+useful for debugging and performance measurements.
+
+You can also compile with profiling to see what functions are taking
+execution time. The backend profile files will be deposited in the
+/pgsql/data/base/dbname/ directory. The client profile file will be put
+in the client's current directory. Linux requires a compile with
+/-DLINUX_PROFILE/ for proper profiling.
+
+
+ 3.8) Why do I get /"Sorry, too many clients"/ when trying to
+ connect?
+
+You need to increase /postmaster/'s limit on how many concurrent backend
+processes it can start.
+
+The default limit is 32 processes. You can increase it by restarting
+/postmaster/ with a suitable /-N/ value or modifying /postgresql.conf/.
+
+Note that if you make /-N/ larger than 32, you must also increase /-B/
+beyond its default of 64; /-B/ must be at least twice /-N/, and probably
+should be more than that for best performance. For large numbers of
+backend processes, you are also likely to find that you need to increase
+various Unix kernel configuration parameters. Things to check include
+the maximum size of shared memory blocks, SHMMAX; the maximum number of
+semaphores, SEMMNS and SEMMNI; the maximum number of processes, NPROC;
+the maximum number of processes per user, MAXUPRC; and the maximum
+number of open files, NFILE and NINODE. The reason that PostgreSQL has a
+limit on the number of allowed backend processes is so your system won't
+run out of resources.
+
+
+ 3.9) What is in the /pgsql_tmp/ directory?
+
+This directory contains temporary files generated by the query executor.
+For example, if a sort needs to be done to satisfy an ORDER BY and the
+sort requires more space than the backend's /-S/ parameter allows, then
+temporary files are created here to hold the extra data.
+
+The temporary files are usually deleted automatically, but might remain
+if a backend crashes during a sort. A stop and restart of the
+/postmaster/ will remove files from those directories.
+
+
+ 3.10) Why do I need to do a dump and restore to upgrade between
+ major PostgreSQL releases?
+
+The PostgreSQL team makes only small changes between minor releases, so
+upgrading from 7.2 to 7.2.1 does not require a dump and restore.
+However, major releases (e.g. from 7.2 to 7.3) often change the internal
+format of system tables and data files. These changes are often complex,
+so we don't maintain backward compatability for data files. A dump
+outputs data in a generic format that can then be loaded in using the
+new internal format.
+
+In releases where the on-disk format does not change, the /pg_upgrade/
+script can be used to upgrade without a dump/restore. The release notes
+mention whether /pg_upgrade/ is available for the release.
+
+------------------------------------------------------------------------
+
+
+ Operational Questions
+
+
+ 4.1) What is the difference between binary cursors and normal
+ cursors?
+
+See the DECLARE manual page for a description.
+
+
+ 4.2) How do I SELECT only the first few rows of a query?
+
+See the FETCH manual page, or use SELECT ... LIMIT....
+
+The entire query may have to be evaluated, even if you only want the
+first few rows. Consider using a query that has an ORDER BY. If there is
+an index that matches the ORDER BY, PostgreSQL may be able to evaluate
+only the first few records requested, or the entire query may have to be
+evaluated until the desired rows have been generated.
+
+
+ 4.3) How do I get a list of tables or other things I can see in
+ /psql/?
+
+You can read the source code for /psql/ in file
+/pgsql/src/bin/psql/describe.c/. It contains SQL commands that generate
+the output for psql's backslash commands. You can also start /psql/ with
+the /-E/ option so it will print out the queries it uses to execute the
+commands you give.
+
+
+ 4.4) How do you remove a column from a table?
+
+This functionality was added in release 7.3 with ALTER TABLE DROP
+COLUMN. In earlier versions, you can do this:
+
+ BEGIN;
+ LOCK TABLE old_table;
+ SELECT ... -- select all columns but the one you want to remove
+ INTO TABLE new_table
+ FROM old_table;
+ DROP TABLE old_table;
+ ALTER TABLE new_table RENAME TO old_table;
+ COMMIT;
+
+
+ 4.5) What is the maximum size for a row, a table, and a database?
+
+These are the limits:
+
+ Maximum size for a database? unlimited (4 TB databases exist)
+ Maximum size for a table? 16 TB
+ Maximum size for a row? 1.6TB
+ Maximum size for a field? 1 GB
+ Maximum number of rows in a table? unlimited
+ Maximum number of columns in a table? 250-1600 depending on column types
+ Maximum number of indexes on a table? unlimited
+
+Of course, these are not actually unlimited, but limited to available
+disk space and memory/swap space. Performance may suffer when these
+values get unusually large.
+
+The maximum table size of 16 TB does not require large file support from
+the operating system. Large tables are stored as multiple 1 GB files so
+file system size limits are not important.
+
+The maximum table size and maximum number of columns can be increased if
+the default block size is increased to 32k.
+
+
+ 4.6) How much database disk space is required to store data from
+ a typical text file?
+
+A PostgreSQL database may require up to five times the disk space to
+store data from a text file.
+
+As an example, consider a file of 100,000 lines with an integer and text
+description on each line. Suppose the text string avergages twenty bytes
+in length. The flat file would be 2.8 MB. The size of the PostgreSQL
+database file containing this data can be estimated as 6.4 MB:
+
+ 36 bytes: each row header (approximate)
+ 24 bytes: one int field and one text field
+ + 4 bytes: pointer on page to tuple
+ ----------------------------------------
+ 64 bytes per row
+
+ The data page size in PostgreSQL is 8192 bytes (8 KB), so:
+
+ 8192 bytes per page
+ ------------------- = 128 rows per database page (rounded down)
+ 64 bytes per row
+
+ 100000 data rows
+ -------------------- = 782 database pages (rounded up)
+ 128 rows per page
+
+782 database pages * 8192 bytes per page = 6,406,144 bytes (6.4 MB)
+
+Indexes do not require as much overhead, but do contain the data that is
+being indexed, so they can be large also.
+
+NULLs are stored in bitmaps, so they use very little space.
+
+
+ 4.7) How do I find out what tables, indexes, databases, and
+ users are defined?
+
+/psql/ has a variety of backslash commands to show such information. Use
+\? to see them. There are also system tables beginning with /pg_/ that
+describe these too. Also, /psql -l/ will list all databases.
+
+Also try the file /pgsql/src/tutorial/syscat.source/. It illustrates
+many of the SELECTs needed to get information from the database system
+tables.
+
+
+ 4.8) My queries are slow or don't make use of the indexes. Why?
+
+Indexes are not automatically used by every query. Indexes are only used
+if the table is larger than a minimum size, and the query selects only a
+small percentage of the rows in the table. This is because the random
+disk access caused by an index scan can be slower than a straight read
+through the table, or sequential scan.
+
+To determine if an index should be used, PostgreSQL must have statistics
+about the table. These statistics are collected using VACUUM ANALYZE, or
+simply ANALYZE. Using statistics, the optimizer knows how many rows are
+in the table, and can better determine if indexes should be used.
+Statistics are also valuable in determining optimal join order and join
+methods. Statistics collection should be performed periodically as the
+contents of the table change.
+
+Indexes are normally not used for ORDER BY or to perform joins. A
+sequential scan followed by an explicit sort is usually faster than an
+index scan of a large table.
+
+However, LIMIT combined with ORDER BY often will use an index because
+only a small portion of the table is returned. In fact, though MAX() and
+MIN() don't use indexes, it is possible to retrieve such values using an
+index with ORDER BY and LIMIT:
+
+ SELECT col
+ FROM tab
+ ORDER BY col [ DESC ]
+ LIMIT 1;
+
+If you believe the optimizer is incorrect in choosing a sequential scan,
+use |SET enable_seqscan TO 'off'| and run tests to see if an index scan
+is indeed faster.
+
+When using wild-card operators such as LIKE or /~/, indexes can only be
+used in certain circumstances:
+
+ * The beginning of the search string must be anchored to the start
+ of the string, i.e.
+ o LIKE patterns must not start with /%/.
+ o /~/ (regular expression) patterns must start with /^/.
+ * The search string can not start with a character class, e.g. [a-e].
+ * Case-insensitive searches such as ILIKE and /~*/ do not utilise
+ indexes. Instead, use functional indexes, which are described in
+ section 4.12 <#4.12>.
+ * The default /C/ locale must be used during /initdb/.
+
+
+ 4.9) How do I see how the query optimizer is evaluating my query?
+
+See the EXPLAIN manual page.
+
+
+ 4.10) What is an R-tree index?
+
+An R-tree index is used for indexing spatial data. A hash index can't
+handle range searches. A B-tree index only handles range searches in a
+single dimension. R-trees can handle multi-dimensional data. For
+example, if an R-tree index can be built on an attribute of type
+/point/, the system can more efficiently answer queries such as "select
+all points within a bounding rectangle."
+
+The canonical paper that describes the original R-tree design is:
+
+Guttman, A. "R-trees: A Dynamic Index Structure for Spatial Searching."
+Proceedings of the 1984 ACM SIGMOD Int'l Conf on Mgmt of Data, 45-57.
+
+You can also find this paper in Stonebraker's "Readings in Database
+Systems".
+
+Built-in R-trees can handle polygons and boxes. In theory, R-trees can
+be extended to handle higher number of dimensions. In practice,
+extending R-trees requires a bit of work and we don't currently have any
+documentation on how to do it.
+
+
+ 4.11) What is the Genetic Query Optimizer?
+
+The GEQO module speeds query optimization when joining many tables by
+means of a Genetic Algorithm (GA). It allows the handling of large join
+queries through nonexhaustive search.
+
+
+ 4.12) How do I perform regular expression searches and
+ case-insensitive regular expression searches? How do I use an
+ index for case-insensitive searches?
+
+The /~/ operator does regular expression matching, and /~*/ does
+case-insensitive regular expression matching. The case-insensitive
+variant of LIKE is called ILIKE.
+
+Case-insensitive equality comparisons are normally expressed as:
+
+ SELECT *
+ FROM tab
+ WHERE lower(col) = 'abc';
+
+This will not use an standard index. However, if you create a functional
+index, it will be used:
+
+ CREATE INDEX tabindex ON tab (lower(col));
+
+
+ 4.13) In a query, how do I detect if a field is NULL?
+
+You test the column with IS NULL and IS NOT NULL.
+
+
+ 4.14) What is the difference between the various character types?
+
+Type Internal Name Notes
+--------------------------------------------------
+VARCHAR(n) varchar size specifies maximum length, no padding
+CHAR(n) bpchar blank padded to the specified fixed length
+TEXT text no specific upper limit on length
+BYTEA bytea variable-length byte array (null-byte safe)
+"char" char one character
+
+You will see the internal name when examining system catalogs and in
+some error messages.
+
+The first four types above are "varlena" types (i.e., the first four
+bytes on disk are the length, followed by the data). Thus the actual
+space used is slightly greater than the declared size. However, these
+data types are also subject to compression or being stored out-of-line
+by TOAST, so the space on disk might also be less than expected.
+
+VARCHAR(n) is best when storing variable-length strings and it limits
+how long a string can be. TEXT is for strings of unlimited length, with
+a maximum of one gigabyte.
+
+CHAR(n) is for storing strings that are all the same length. CHAR(n)
+pads with blanks to the specified length, while VARCHAR(n) only stores
+the characters supplied. BYTEA is for storing binary data, particularly
+values that include NULL bytes. All the types described here have
+similar performance characteristics.
+
+
+ 4.15.1) How do I create a serial/auto-incrementing field?
+
+PostgreSQL supports a SERIAL data type. It auto-creates a sequence and
+index on the column. For example, this:
+
+ CREATE TABLE person (
+ id SERIAL,
+ name TEXT
+ );
+
+is automatically translated into this:
+
+ CREATE SEQUENCE person_id_seq;
+ CREATE TABLE person (
+ id INT4 NOT NULL DEFAULT nextval('person_id_seq'),
+ name TEXT
+ );
+ CREATE UNIQUE INDEX person_id_key ON person ( id );
+
+See the /create_sequence/ manual page for more information about
+sequences. You can also use each row's /OID/ field as a unique value.
+However, if you need to dump and reload the database, you need to use
+/pg_dump/'s /-o/ option or COPY WITH OIDS option to preserve the OIDs.
+
+
+ 4.15.2) How do I get the value of a SERIAL insert?
+
+One approach is to retrieve the next SERIAL value from the sequence
+object with the /nextval()/ function /before/ inserting and then insert
+it explicitly. Using the example table in 4.15.1 <#4.15.1>, an example
+in a pseudo-language would look like this:
+
+ new_id = execute("SELECT nextval('person_id_seq')");
+ execute("INSERT INTO person (id, name) VALUES (new_id, 'Blaise Pascal')");
+
+You would then also have the new value stored in |new_id| for use in
+other queries (e.g., as a foreign key to the |person| table). Note that
+the name of the automatically created SEQUENCE object will be named
+</table/>_</serialcolumn/>_/seq/, where /table/ and /serialcolumn/ are
+the names of your table and your SERIAL column, respectively.
+
+Alternatively, you could retrieve the assigned SERIAL value with the
+/currval()/ function /after/ it was inserted by default, e.g.,
+
+ execute("INSERT INTO person (name) VALUES ('Blaise Pascal')");
+ new_id = execute("SELECT currval('person_id_seq')");
+
+Finally, you could use the OID <#4.16> returned from the INSERT
+statement to look up the default value, though this is probably the
+least portable approach. In Perl, using DBI with Edmund Mergl's DBD::Pg
+module, the oid value is made available via /$sth->{pg_oid_status}/
+after /$sth->execute()/.
+
+
+ 4.15.3) Don't /currval()/ and /nextval()/ lead to a race
+ condition with other users?
+
+No. /currval()/ returns the current value assigned by your backend, not
+by all users.
+
+
+ 4.15.4) Why aren't my sequence numbers reused on transaction
+ abort? Why are there gaps in the numbering of my sequence/SERIAL
+ column?
+
+To improve concurrency, sequence values are given out to running
+transactions as needed and are not locked until the transaction
+completes. This causes gaps in numbering from aborted transactions.
+
+
+ 4.16) What is an OID? What is a TID?
+
+OIDs are PostgreSQL's answer to unique row ids. Every row that is
+created in PostgreSQL gets a unique OID. All OIDs generated during
+/initdb/ are less than 16384 (from /include/access/transam.h/). All
+user-created OIDs are equal to or greater than this. By default, all
+these OIDs are unique not only within a table or database, but unique
+within the entire PostgreSQL installation.
+
+PostgreSQL uses OIDs in its internal system tables to link rows between
+tables. These OIDs can be used to identify specific user rows and used
+in joins. It is recommended you use column type OID to store OID values.
+You can create an index on the OID field for faster access.
+
+OIDs are assigned to all new rows from a central area that is used by
+all databases. If you want to change the OID to something else, or if
+you want to make a copy of the table, with the original OIDs, there is
+no reason you can't do it:
+
+ CREATE TABLE new_table(old_oid oid, mycol int);
+ SELECT old_oid, mycol INTO new FROM old;
+ COPY new TO '/tmp/pgtable';
+ DELETE FROM new;
+ COPY new WITH OIDS FROM '/tmp/pgtable';
+
+OIDs are stored as 4-byte integers, and will overflow at 4 billion. No
+one has reported this ever happening, and we plan to have the limit
+removed before anyone does.
+
+TIDs are used to identify specific physical rows with block and offset
+values. TIDs change after rows are modified or reloaded. They are used
+by index entries to point to physical rows.
+
+
+ 4.17) What is the meaning of some of the terms used in PostgreSQL?
+
+Some of the source code and older documentation use terms that have more
+common usage. Here are some:
+
+ * table, relation, class
+ * row, record, tuple
+ * column, field, attribute
+ * retrieve, select
+ * replace, update
+ * append, insert
+ * OID, serial value
+ * portal, cursor
+ * range variable, table name, table alias
+
+A list of general database terms can be found at:
+http://hea-www.harvard.edu/MST/simul/software/docs/pkgs/pgsql/glossary/glossary.html
+
+
+ 4.18) Why do I get the error /"ERROR: Memory exhausted in
+ AllocSetAlloc()"/?
+
+You probably have run out of virtual memory on your system, or your
+kernel has a low limit for certain resources. Try this before starting
+/postmaster/:
+
+ ulimit -d 262144
+ limit datasize 256m
+
+Depending on your shell, only one of these may succeed, but it will set
+your process data segment limit much higher and perhaps allow the query
+to complete. This command applies to the current process, and all
+subprocesses created after the command is run. If you are having a
+problem with the SQL client because the backend is returning too much
+data, try it before starting the client.
+
+
+ 4.19) How do I tell what PostgreSQL version I am running?
+
+From /psql/, type |SELECT version();|
+
+
+ 4.20) Why does my large-object operations get /"invalid large
+ obj descriptor"/?
+
+You need to put |BEGIN WORK| and |COMMIT| around any use of a large
+object handle, that is, surrounding |lo_open| ... |lo_close.|
+
+Currently PostgreSQL enforces the rule by closing large object handles
+at transaction commit. So the first attempt to do anything with the
+handle will draw /invalid large obj descriptor/. So code that used to
+work (at least most of the time) will now generate that error message if
+you fail to use a transaction.
+
+If you are using a client interface like ODBC you may need to set
+|auto-commit off.|
+
+
+ 4.21) How do I create a column that will default to the current
+ time?
+
+Use /CURRENT_TIMESTAMP/:
+
+|CREATE TABLE test (x int, modtime timestamp DEFAULT CURRENT_TIMESTAMP );
+|
+
+
+ 4.22) Why are my subqueries using |IN| so slow?
+
+Currently, we join subqueries to outer queries by sequentially scanning
+the result of the subquery for each row of the outer query. If the
+subquery returns only a few rows and the outer query returns many rows,
+|IN| is fastest. To speed up other queries, replace |IN| with |EXISTS|:
+
+ SELECT *
+ FROM tab
+ WHERE col IN (SELECT subcol FROM subtab);
+
+to:
+
+ SELECT *
+ FROM tab
+ WHERE EXISTS (SELECT subcol FROM subtab WHERE subcol = col);
+
+For this to be fast, |subcol| should be an indexed column. This
+preformance problem will be fixed in 7.4.
+
+
+ 4.23) How do I perform an outer join?
+
+PostgreSQL supports outer joins using the SQL standard syntax. Here are
+two examples:
+
+ SELECT *
+ FROM t1 LEFT OUTER JOIN t2 ON (t1.col = t2.col);
+
+or
+
+ SELECT *
+ FROM t1 LEFT OUTER JOIN t2 USING (col);
+
+These identical queries join t1.col to t2.col, and also return any
+unjoined rows in t1 (those with no match in t2). A RIGHT join would add
+unjoined rows of t2. A FULL join would return the matched rows plus all
+unjoined rows from t1 and t2. The word OUTER is optional and is assumed
+in LEFT, RIGHT, and FULL joins. Ordinary joins are called INNER joins.
+
+In previous releases, outer joins can be simulated using UNION and NOT
+IN. For example, when joining /tab1/ and /tab2/, the following query
+does an /outer/ join of the two tables:
+
+ SELECT tab1.col1, tab2.col2
+ FROM tab1, tab2
+ WHERE tab1.col1 = tab2.col1
+ UNION ALL
+ SELECT tab1.col1, NULL
+ FROM tab1
+ WHERE tab1.col1 NOT IN (SELECT tab2.col1 FROM tab2)
+ ORDER BY col1
+
+
+ 4.24) How do I perform queries using multiple databases?
+
+There is no way to query a database other than the current one. Because
+PostgreSQL loads database-specific system catalogs, it is uncertain how
+a cross-database query should even behave.
+
+/contrib/dblink/ allows cross-database queries using function calls. Of
+course, a client can make simultaneous connections to different
+databases and merge the results on the client side.
+
+
+ 4.25) How do I return multiple rows or columns from a function?
+
+In 7.3, you can easily return multiple rows or columns from a function,
+http://techdocs.postgresql.org/guides/SetReturningFunctions
+<http://techdocs.postgresql.org/guides/SetReturningFunctions>.
+
+
+ 4.26) Why can't I reliably create/drop temporary tables in
+ PL/PgSQL functions?
+
+PL/PgSQL caches function contents, and an unfortunate side effect is
+that if a PL/PgSQL function accesses a temporary table, and that table
+is later dropped and recreated, and the function called again, the
+function will fail because the cached function contents still point to
+the old temporary table. The solution is to use EXECUTE for temporary
+table access in PL/PgSQL. This will cause the query to be reparsed every
+time.
+
+
+ 4.27) What replication options are available?
+
+There are several master/slave replication options available. These
+allow only the master to make database changes and the slave can only do
+database reads. The bottom of
+http://gborg.PostgreSQL.org/genpage?replication_research
+<http://gborg.PostgreSQL.org/genpage?replication_research> lists them. A
+multi-master replication solution is being worked on at
+http://gborg.PostgreSQL.org/project/pgreplication/projdisplay.php.
+
+
+ 4.28) What encryption options are available?
+
+ * /contrib/pgcrypto/ contains many encryption functions for use in
+ SQL queries.
+ * The only way to encrypt transmission from the client to the server
+ is by using /hostssl/ in /pg_hba.conf/.
+ * Database user passwords are automatically encrypted when stored in
+ version 7.3. In previous versions, you must enable the option
+ /PASSWORD_ENCRYPTION/ in /postgresql.conf/.
+ * The server can run using an encrypted file system.
+
+------------------------------------------------------------------------
+
+
+ Extending PostgreSQL
+
+
+ 5.1) I wrote a user-defined function. When I run it in /psql/,
+ why does it dump core?
+
+The problem could be a number of things. Try testing your user-defined
+function in a stand-alone test program first.
+
+
+ 5.2) How can I contribute some nifty new types and functions to
+ PostgreSQL?
+
+Send your extensions to the /pgsql-hackers/ mailing list, and they will
+eventually end up in the /contrib// subdirectory.
+
+
+ 5.3) How do I write a C function to return a tuple?
+
+In versions of PostgreSQL beginning with 7.3, table-returning functions
+are fully supported in C, PL/PgSQL, and SQL. See the Programmer's Guide
+for more information. An example of a table-returning function defined
+in C can be found in /contrib/tablefunc/.
+
+
+ 5.4) I have changed a source file. Why does the recompile not
+ see the change?
+
+The /Makefiles/ do not have the proper dependencies for include files.
+You have to do a /make clean/ and then another /make/. If you are using
+GCC you can use the /--enable-depend/ option of /configure/ to have the
+compiler compute the dependencies automatically.
+