From e0de8d98214d514d1e120bdcf1b72d03899e04e2 Mon Sep 17 00:00:00 2001
From: Bruce Momjian <bruce@momjian.us>
Date: Sat, 29 Dec 2001 03:42:59 +0000
Subject: [PATCH] Update FAQ_DEV.
---
doc/FAQ_DEV | 681 ++++++++++++++--------------
doc/src/FAQ/FAQ_DEV.html | 956 ++++++++++++++++++++-------------------
2 files changed, 827 insertions(+), 810 deletions(-)
diff --git a/doc/FAQ_DEV b/doc/FAQ_DEV
index d5faef76a0c..073a3917a1d 100644
--- a/doc/FAQ_DEV
+++ b/doc/FAQ_DEV
@@ -9,31 +9,146 @@
postgreSQL Web site, http://www.PostgreSQL.org.
_________________________________________________________________
- Questions
+ General Questions
- 1) What tools are available for developers?
- 2) What books are good for developers?
- 3) Why do we use palloc() and pfree() to allocate memory?
- 4) Why do we use Node and List to make data structures?
- 5) How do I add a feature or fix a bug?
- 6) How do I download/update the current source tree?
- 7) How do I test my changes?
- 7) I just added a field to a structure. What else should I do?
- 8) Why are table, column, type, function, view names sometimes
+ 1.1) How do I get involved in PostgreSQL development?
+ 1.2) How do I add a feature or fix a bug?
+ 1.3) How do I download/update the current source tree?
+ 1.4) How do I test my changes?
+ 1.5) What tools are available for developers?
+ 1.6) What books are good for developers?
+ 1.7) What is configure all about?
+ 1.8) How do I add a new port?
+ 1.9) Why don't we use threads in the backend?
+ 1.10) How are RPM's packaged?
+ 1.11) How are CVS branches handled?
+
+Technical Questions
+
+ 2.1) How do I efficiently access information in tables from the
+ backend code?
+ 2.2) Why are table, column, type, function, view names sometimes
referenced as Name or NameData, and sometimes as char *?
- 9) How do I efficiently access information in tables from the backend
- code?
- 10) What is elog()?
- 11) What is configure all about?
- 12) How do I add a new port?
- 13) What is CommandCounterIncrement()?
- 14) Why don't we use threads in the backend?
- 15) How are RPM's packaged?
- 16) How are CVS branches handled?
- 17) How do I get involved in PostgreSQL development?
+ 2.3) Why do we use Node and List to make data structures?
+ 2.4) I just added a field to a structure. What else should I do?
+ 2.5) Why do we use palloc() and pfree() to allocate memory?
+ 2.6) What is elog()?
+ 2.7) What is CommandCounterIncrement()?
_________________________________________________________________
- 1) What tools are available for developers?
+ General Questions
+
+ 1.1) How go I get involved in PostgreSQL development?
+
+ This was written by Lamar Owen:
+
+ 2001-06-22
+ What open source development process is used by the PostgreSQL team?
+
+ Read HACKERS for six months (or a full release cycle, whichever is
+ longer). Really. HACKERS _is_the process. The process is not well
+ documented (AFAIK -- it may be somewhere that I am not aware of) --
+ and it changes continually.
+ What development environment (OS, system, compilers, etc) is required
+ to develop code?
+
+ Developers Corner on the website has links to this information. The
+ distribution tarball itself includes all the extra tools and documents
+ that go beyond a good Unix-like development environment. In general, a
+ modern unix with a modern gcc, GNU make or equivalent, autoconf (of a
+ particular version), and good working knowledge of those tools are
+ required.
+ What areas need support?
+
+ The TODO list.
+
+ You've made the first step, by finding and subscribing to HACKERS.
+ Once you find an area to look at in the TODO, and have read the
+ documentation on the internals, etc, then you check out a current
+ CVS,write what you are going to write (keeping your CVS checkout up to
+ date in the process), and make up a patch (as a context diff only) and
+ send to the PATCHES list, prefereably.
+
+ Discussion on the patch typically happens here. If the patch adds a
+ major feature, it would be a good idea to talk about it first on the
+ HACKERS list, in order to increase the chances of it being accepted,
+ as well as toavoid duplication of effort. Note that experienced
+ developers with a proven track record usually get the big jobs -- for
+ more than one reason. Also note that PostgreSQL is highly portable --
+ nonportable code will likely be dismissed out of hand.
+
+ Once your contributions get accepted, things move from there.
+ Typically, you would be added as a developer on the list on the
+ website when one of the other developers recommends it. Membership on
+ the steering committee is by invitation only, by the other steering
+ committee members, from what I have gathered watching froma distance.
+
+ I make these statements from having watched the process for over two
+ years.
+
+ To see a good example of how one goes about this, search the archives
+ for the name 'Tom Lane' and see what his first post consisted of, and
+ where he took things. In particular, note that this hasn't been _that_
+ long ago -- and his bugfixing and general deep knowledge with this
+ codebase is legendary. Take a few days to read after him. And pay
+ special attention to both the sheer quantity as well as the
+ painstaking quality of his work. Both are in high demand.
+
+ 1.2) How do I add a feature or fix a bug?
+
+ The source code is over 250,000 lines. Many problems/features are
+ isolated to one specific area of the code. Others require knowledge of
+ much of the source. If you are confused about where to start, ask the
+ hackers list, and they will be glad to assess the complexity and give
+ pointers on where to start.
+
+ Another thing to keep in mind is that many fixes and features can be
+ added with surprisingly little code. I often start by adding code,
+ then looking at other areas in the code where similar things are done,
+ and by the time I am finished, the patch is quite small and compact.
+
+ When adding code, keep in mind that it should use the existing
+ facilities in the source, for performance reasons and for simplicity.
+ Often a review of existing code doing similar things is helpful.
+
+ 1.3) How do I download/update the current source tree?
+
+ There are several ways to obtain the source tree. Occasional
+ developers can just get the most recent source tree snapshot from
+ ftp.postgresql.org. For regular developers, you can use CVS. CVS
+ allows you to download the source tree, then occasionally update your
+ copy of the source tree with any new changes. Using CVS, you don't
+ have to download the entire source each time, only the changed files.
+ Anonymous CVS does not allows developers to update the remote source
+ tree, though privileged developers can do this. There is a CVS FAQ on
+ our web site that describes how to use remote CVS. You can also use
+ CVSup, which has similarly functionality, and is available from
+ ftp.postgresql.org.
+
+ To update the source tree, there are two ways. You can generate a
+ patch against your current source tree, perhaps using the make_diff
+ tools mentioned above, and send them to the patches list. They will be
+ reviewed, and applied in a timely manner. If the patch is major, and
+ we are in beta testing, the developers may wait for the final release
+ before applying your patches.
+
+ For hard-core developers, Marc(scrappy@postgresql.org) will give you a
+ Unix shell account on postgresql.org, so you can use CVS to update the
+ main source tree, or you can ftp your files into your account, patch,
+ and cvs install the changes directly into the source tree.
+
+ 1.4) How do I test my changes?
+
+ First, use psql to make sure it is working as you expect. Then run
+ src/test/regress and get the output of src/test/regress/checkresults
+ with and without your changes, to see that your patch does not change
+ the regression test in unexpected ways. This practice has saved me
+ many times. The regression tests test the code in ways I would never
+ do, and has caught many bugs in my patches. By finding the problems
+ now, you save yourself a lot of debugging later when things are
+ broken, and you can't figure out when it happened.
+
+ 1.5) What tools are available for developers?
Aside from the User documentation mentioned in the regular FAQ, there
are several development tools available. First, all the files in the
@@ -126,264 +241,32 @@
*/
pgindent will the format code by specifying flags to your operating
- system's utility indent.
-
- pgindent is run on all source files just before each beta test period.
- It auto-formats all source files to make them consistent. Comment
- blocks that need specific line breaks should be formatted as block
- comments, where the comment starts as /*------. These comments will
- not be reformatted in any way.
-
- pginclude contains scripts used to add needed #include's to include
- files, and removed unneeded #include's.
-
- When adding system types, you will need to assign oids to them. There
- is also a script called unused_oids in pgsql/src/include/catalog that
- shows the unused oids.
-
- 2) What books are good for developers?
-
- I have four good books, An Introduction to Database Systems, by C.J.
- Date, Addison, Wesley, A Guide to the SQL Standard, by C.J. Date, et.
- al, Addison, Wesley, Fundamentals of Database Systems, by Elmasri and
- Navathe, and Transaction Processing, by Jim Gray, Morgan, Kaufmann
-
- There is also a database performance site, with a handbook on-line
- written by Jim Gray at http://www.benchmarkresources.com.
-
- 3) Why do we use palloc() and pfree() to allocate memory?
-
- palloc() and pfree() are used in place of malloc() and free() because
- we automatically free all memory allocated when a transaction
- completes. This makes it easier to make sure we free memory that gets
- allocated in one place, but only freed much later. There are several
- contexts that memory can be allocated in, and this controls when the
- allocated memory is automatically freed by the backend.
-
- 4) Why do we use Node and List to make data structures?
-
- We do this because this allows a consistent way to pass data inside
- the backend in a flexible way. Every node has a NodeTag which
- specifies what type of data is inside the Node. Lists are groups of
- Nodes chained together as a forward-linked list.
-
- Here are some of the List manipulation commands:
-
- lfirst(i)
- return the data at list element i.
-
- lnext(i)
- return the next list element after i.
-
- foreach(i, list)
- loop through list, assigning each list element to i. It is
- important to note that i is a List *, not the data in the List
- element. You need to use lfirst(i) to get at the data. Here is
- a typical code snipped that loops through a List containing Var
- *'s and processes each one:
-
-List *i, *list;
-
- foreach(i, list)
- {
- Var *var = lfirst(i);
-
- /* process var here */
- }
-
- lcons(node, list)
- add node to the front of list, or create a new list with node
- if list is NIL.
-
- lappend(list, node)
- add node to the end of list. This is more expensive that lcons.
-
- nconc(list1, list2)
- Concat list2 on to the end of list1.
-
- length(list)
- return the length of the list.
-
- nth(i, list)
- return the i'th element in list.
-
- lconsi, ...
- There are integer versions of these: lconsi, lappendi, nthi.
- List's containing integers instead of Node pointers are used to
- hold list of relation object id's and other integer quantities.
-
- You can print nodes easily inside gdb. First, to disable output
- truncation when you use the gdb print command:
-(gdb) set print elements 0
-
- Instead of printing values in gdb format, you can use the next two
- commands to print out List, Node, and structure contents in a verbose
- format that is easier to understand. List's are unrolled into nodes,
- and nodes are printed in detail. The first prints in a short format,
- and the second in a long format:
-(gdb) call print(any_pointer)
- (gdb) call pprint(any_pointer)
-
- The output appears in the postmaster log file, or on your screen if
- you are running a backend directly without a postmaster.
-
- 5) How do I add a feature or fix a bug?
-
- The source code is over 250,000 lines. Many problems/features are
- isolated to one specific area of the code. Others require knowledge of
- much of the source. If you are confused about where to start, ask the
- hackers list, and they will be glad to assess the complexity and give
- pointers on where to start.
-
- Another thing to keep in mind is that many fixes and features can be
- added with surprisingly little code. I often start by adding code,
- then looking at other areas in the code where similar things are done,
- and by the time I am finished, the patch is quite small and compact.
-
- When adding code, keep in mind that it should use the existing
- facilities in the source, for performance reasons and for simplicity.
- Often a review of existing code doing similar things is helpful.
-
- 6) How do I download/update the current source tree?
-
- There are several ways to obtain the source tree. Occasional
- developers can just get the most recent source tree snapshot from
- ftp.postgresql.org. For regular developers, you can use CVS. CVS
- allows you to download the source tree, then occasionally update your
- copy of the source tree with any new changes. Using CVS, you don't
- have to download the entire source each time, only the changed files.
- Anonymous CVS does not allows developers to update the remote source
- tree, though privileged developers can do this. There is a CVS FAQ on
- our web site that describes how to use remote CVS. You can also use
- CVSup, which has similarly functionality, and is available from
- ftp.postgresql.org.
-
- To update the source tree, there are two ways. You can generate a
- patch against your current source tree, perhaps using the make_diff
- tools mentioned above, and send them to the patches list. They will be
- reviewed, and applied in a timely manner. If the patch is major, and
- we are in beta testing, the developers may wait for the final release
- before applying your patches.
-
- For hard-core developers, Marc(scrappy@postgresql.org) will give you a
- Unix shell account on postgresql.org, so you can use CVS to update the
- main source tree, or you can ftp your files into your account, patch,
- and cvs install the changes directly into the source tree.
-
- 6) How do I test my changes?
-
- First, use psql to make sure it is working as you expect. Then run
- src/test/regress and get the output of src/test/regress/checkresults
- with and without your changes, to see that your patch does not change
- the regression test in unexpected ways. This practice has saved me
- many times. The regression tests test the code in ways I would never
- do, and has caught many bugs in my patches. By finding the problems
- now, you save yourself a lot of debugging later when things are
- broken, and you can't figure out when it happened.
-
- 7) I just added a field to a structure. What else should I do?
-
- The structures passing around from the parser, rewrite, optimizer, and
- executor require quite a bit of support. Most structures have support
- routines in src/backend/nodes used to create, copy, read, and output
- those structures. Make sure you add support for your new field to
- these files. Find any other places the structure may need code for
- your new field. mkid is helpful with this (see above).
-
- 8) Why are table, column, type, function, view names sometimes referenced as
- Name or NameData, and sometimes as char *?
-
- Table, column, type, function, and view names are stored in system
- tables in columns of type Name. Name is a fixed-length,
- null-terminated type of NAMEDATALEN bytes. (The default value for
- NAMEDATALEN is 32 bytes.)
-typedef struct nameData
- {
- char data[NAMEDATALEN];
- } NameData;
- typedef NameData *Name;
-
- Table, column, type, function, and view names that come into the
- backend via user queries are stored as variable-length,
- null-terminated character strings.
-
- Many functions are called with both types of names, ie. heap_open().
- Because the Name type is null-terminated, it is safe to pass it to a
- function expecting a char *. Because there are many cases where
- on-disk names(Name) are compared to user-supplied names(char *), there
- are many cases where Name and char * are used interchangeably.
-
- 9) How do I efficiently access information in tables from the backend code?
-
- You first need to find the tuples(rows) you are interested in. There
- are two ways. First, SearchSysCache() and related functions allow you
- to query the system catalogs. This is the preferred way to access
- system tables, because the first call to the cache loads the needed
- rows, and future requests can return the results without accessing the
- base table. The caches use system table indexes to look up tuples. A
- list of available caches is located in
- src/backend/utils/cache/syscache.c.
- src/backend/utils/cache/lsyscache.c contains many column-specific
- cache lookup functions.
-
- The rows returned are cache-owned versions of the heap rows.
- Therefore, you must not modify or delete the tuple returned by
- SearchSysCache(). What you should do is release it with
- ReleaseSysCache() when you are done using it; this informs the cache
- that it can discard that tuple if necessary. If you neglect to call
- ReleaseSysCache(), then the cache entry will remain locked in the
- cache until end of transaction, which is tolerable but not very
- desirable.
-
- If you can't use the system cache, you will need to retrieve the data
- directly from the heap table, using the buffer cache that is shared by
- all backends. The backend automatically takes care of loading the rows
- into the buffer cache.
-
- Open the table with heap_open(). You can then start a table scan with
- heap_beginscan(), then use heap_getnext() and continue as long as
- HeapTupleIsValid() returns true. Then do a heap_endscan(). Keys can be
- assigned to the scan. No indexes are used, so all rows are going to be
- compared to the keys, and only the valid rows returned.
-
- You can also use heap_fetch() to fetch rows by block number/offset.
- While scans automatically lock/unlock rows from the buffer cache, with
- heap_fetch(), you must pass a Buffer pointer, and ReleaseBuffer() it
- when completed.
-
- Once you have the row, you can get data that is common to all tuples,
- like t_self and t_oid, by merely accessing the HeapTuple structure
- entries. If you need a table-specific column, you should take the
- HeapTuple pointer, and use the GETSTRUCT() macro to access the
- table-specific start of the tuple. You then cast the pointer as a
- Form_pg_proc pointer if you are accessing the pg_proc table, or
- Form_pg_type if you are accessing pg_type. You can then access the
- columns by using a structure pointer:
-((Form_pg_class) GETSTRUCT(tuple))->relnatts
-
- You must not directly change live tuples in this way. The best way is
- to use heap_modifytuple() and pass it your original tuple, and the
- values you want changed. It returns a palloc'ed tuple, which you pass
- to heap_replace(). You can delete tuples by passing the tuple's t_self
- to heap_destroy(). You use t_self for heap_update() too. Remember,
- tuples can be either system cache copies, which may go away after you
- call ReleaseSysCache(), or read directly from disk buffers, which go
- away when you heap_getnext(), heap_endscan, or ReleaseBuffer(), in the
- heap_fetch() case. Or it may be a palloc'ed tuple, that you must
- pfree() when finished.
+ system's utility indent.
+
+ pgindent is run on all source files just before each beta test period.
+ It auto-formats all source files to make them consistent. Comment
+ blocks that need specific line breaks should be formatted as block
+ comments, where the comment starts as /*------. These comments will
+ not be reformatted in any way.
+
+ pginclude contains scripts used to add needed #include's to include
+ files, and removed unneeded #include's.
+
+ When adding system types, you will need to assign oids to them. There
+ is also a script called unused_oids in pgsql/src/include/catalog that
+ shows the unused oids.
- 10) What is elog()?
+ 1.6) What books are good for developers?
- elog() is used to send messages to the front-end, and optionally
- terminate the current query being processed. The first parameter is an
- elog level of NOTICE, DEBUG, ERROR, or FATAL. NOTICE prints on the
- user's terminal and the postmaster logs. DEBUG prints only in the
- postmaster logs. ERROR prints in both places, and terminates the
- current query, never returning from the call. FATAL terminates the
- backend process. The remaining parameters of elog are a printf-style
- set of parameters to print.
+ I have four good books, An Introduction to Database Systems, by C.J.
+ Date, Addison, Wesley, A Guide to the SQL Standard, by C.J. Date, et.
+ al, Addison, Wesley, Fundamentals of Database Systems, by Elmasri and
+ Navathe, and Transaction Processing, by Jim Gray, Morgan, Kaufmann
+
+ There is also a database performance site, with a handbook on-line
+ written by Jim Gray at http://www.benchmarkresources.com.
- 11) What is configure all about?
+ 1.7) What is configure all about?
The files configure and configure.in are part of the GNU autoconf
package. Configure allows us to test for various capabilities of the
@@ -405,7 +288,7 @@ typedef struct nameData
removed, so you see only the file contained in the source
distribution.
- 12) How do I add a new port?
+ 1.8) How do I add a new port?
There are a variety of places that need to be modified to add a new
port. First, start in the src/template directory. Add an appropriate
@@ -422,19 +305,7 @@ typedef struct nameData
src/makefiles directory for port-specific Makefile handling. There is
a backend/port directory if you need special files for your OS.
- 13) What is CommandCounterIncrement()?
-
- Normally, transactions can not see the rows they modify. This allows
- UPDATE foo SET x = x + 1 to work correctly.
-
- However, there are cases where a transactions needs to see rows
- affected in previous parts of the transaction. This is accomplished
- using a Command Counter. Incrementing the counter allows transactions
- to be broken into pieces so each piece can see rows modified by
- previous pieces. CommandCounterIncrement() increments the Command
- Counter, creating a new part of the transaction.
-
- 14) Why don't we use threads in the backend?
+ 1.9) Why don't we use threads in the backend?
There are several reasons threads are not used:
* Historically, threads were unsupported and buggy.
@@ -443,7 +314,7 @@ typedef struct nameData
remaining backend startup time.
* The backend code would be more complex.
- 15) How are RPM's packaged?
+ 1.10) How are RPM's packaged?
This was written by Lamar Owen:
@@ -538,7 +409,7 @@ typedef struct nameData
Of course, there are many projects that DO include all the files
necessary to build RPMs from their Official Tarball (TM).
- 16) How are CVS branches managed?
+ 1.11) How are CVS branches managed?
This was written by Tom Lane:
@@ -597,58 +468,194 @@ typedef struct nameData
tree right away after a major release --- we wait for a dot-release or
two, so that we won't have to double-patch the first wave of fixes.
- 17) How go I get involved in PostgreSQL development?
+ Technical Questions
+
+ 2.1) How do I efficiently access information in tables from the backend code?
- This was written by Lamar Owen:
+ You first need to find the tuples(rows) you are interested in. There
+ are two ways. First, SearchSysCache() and related functions allow you
+ to query the system catalogs. This is the preferred way to access
+ system tables, because the first call to the cache loads the needed
+ rows, and future requests can return the results without accessing the
+ base table. The caches use system table indexes to look up tuples. A
+ list of available caches is located in
+ src/backend/utils/cache/syscache.c.
+ src/backend/utils/cache/lsyscache.c contains many column-specific
+ cache lookup functions.
- 2001-06-22
- What open source development process is used by the PostgreSQL team?
+ The rows returned are cache-owned versions of the heap rows.
+ Therefore, you must not modify or delete the tuple returned by
+ SearchSysCache(). What you should do is release it with
+ ReleaseSysCache() when you are done using it; this informs the cache
+ that it can discard that tuple if necessary. If you neglect to call
+ ReleaseSysCache(), then the cache entry will remain locked in the
+ cache until end of transaction, which is tolerable but not very
+ desirable.
- Read HACKERS for six months (or a full release cycle, whichever is
- longer). Really. HACKERS _is_the process. The process is not well
- documented (AFAIK -- it may be somewhere that I am not aware of) --
- and it changes continually.
- What development environment (OS, system, compilers, etc) is required
- to develop code?
+ If you can't use the system cache, you will need to retrieve the data
+ directly from the heap table, using the buffer cache that is shared by
+ all backends. The backend automatically takes care of loading the rows
+ into the buffer cache.
- Developers Corner on the website has links to this information. The
- distribution tarball itself includes all the extra tools and documents
- that go beyond a good Unix-like development environment. In general, a
- modern unix with a modern gcc, GNU make or equivalent, autoconf (of a
- particular version), and good working knowledge of those tools are
- required.
- What areas need support?
+ Open the table with heap_open(). You can then start a table scan with
+ heap_beginscan(), then use heap_getnext() and continue as long as
+ HeapTupleIsValid() returns true. Then do a heap_endscan(). Keys can be
+ assigned to the scan. No indexes are used, so all rows are going to be
+ compared to the keys, and only the valid rows returned.
- The TODO list.
+ You can also use heap_fetch() to fetch rows by block number/offset.
+ While scans automatically lock/unlock rows from the buffer cache, with
+ heap_fetch(), you must pass a Buffer pointer, and ReleaseBuffer() it
+ when completed.
- You've made the first step, by finding and subscribing to HACKERS.
- Once you find an area to look at in the TODO, and have read the
- documentation on the internals, etc, then you check out a current
- CVS,write what you are going to write (keeping your CVS checkout up to
- date in the process), and make up a patch (as a context diff only) and
- send to the PATCHES list, prefereably.
+ Once you have the row, you can get data that is common to all tuples,
+ like t_self and t_oid, by merely accessing the HeapTuple structure
+ entries. If you need a table-specific column, you should take the
+ HeapTuple pointer, and use the GETSTRUCT() macro to access the
+ table-specific start of the tuple. You then cast the pointer as a
+ Form_pg_proc pointer if you are accessing the pg_proc table, or
+ Form_pg_type if you are accessing pg_type. You can then access the
+ columns by using a structure pointer:
+((Form_pg_class) GETSTRUCT(tuple))->relnatts
+
+ You must not directly change live tuples in this way. The best way is
+ to use heap_modifytuple() and pass it your original tuple, and the
+ values you want changed. It returns a palloc'ed tuple, which you pass
+ to heap_replace(). You can delete tuples by passing the tuple's t_self
+ to heap_destroy(). You use t_self for heap_update() too. Remember,
+ tuples can be either system cache copies, which may go away after you
+ call ReleaseSysCache(), or read directly from disk buffers, which go
+ away when you heap_getnext(), heap_endscan, or ReleaseBuffer(), in the
+ heap_fetch() case. Or it may be a palloc'ed tuple, that you must
+ pfree() when finished.
- Discussion on the patch typically happens here. If the patch adds a
- major feature, it would be a good idea to talk about it first on the
- HACKERS list, in order to increase the chances of it being accepted,
- as well as toavoid duplication of effort. Note that experienced
- developers with a proven track record usually get the big jobs -- for
- more than one reason. Also note that PostgreSQL is highly portable --
- nonportable code will likely be dismissed out of hand.
+ 2.2) Why are table, column, type, function, view names sometimes referenced
+ as Name or NameData, and sometimes as char *?
+
+ Table, column, type, function, and view names are stored in system
+ tables in columns of type Name. Name is a fixed-length,
+ null-terminated type of NAMEDATALEN bytes. (The default value for
+ NAMEDATALEN is 32 bytes.)
+typedef struct nameData
+ {
+ char data[NAMEDATALEN];
+ } NameData;
+ typedef NameData *Name;
+
+ Table, column, type, function, and view names that come into the
+ backend via user queries are stored as variable-length,
+ null-terminated character strings.
- Once your contributions get accepted, things move from there.
- Typically, you would be added as a developer on the list on the
- website when one of the other developers recommends it. Membership on
- the steering committee is by invitation only, by the other steering
- committee members, from what I have gathered watching froma distance.
+ Many functions are called with both types of names, ie. heap_open().
+ Because the Name type is null-terminated, it is safe to pass it to a
+ function expecting a char *. Because there are many cases where
+ on-disk names(Name) are compared to user-supplied names(char *), there
+ are many cases where Name and char * are used interchangeably.
- I make these statements from having watched the process for over two
- years.
+ 2.3) Why do we use Node and List to make data structures?
+
+ We do this because this allows a consistent way to pass data inside
+ the backend in a flexible way. Every node has a NodeTag which
+ specifies what type of data is inside the Node. Lists are groups of
+ Nodes chained together as a forward-linked list.
- To see a good example of how one goes about this, search the archives
- for the name 'Tom Lane' and see what his first post consisted of, and
- where he took things. In particular, note that this hasn't been _that_
- long ago -- and his bugfixing and general deep knowledge with this
- codebase is legendary. Take a few days to read after him. And pay
- special attention to both the sheer quantity as well as the
- painstaking quality of his work. Both are in high demand.
+ Here are some of the List manipulation commands:
+
+ lfirst(i)
+ return the data at list element i.
+
+ lnext(i)
+ return the next list element after i.
+
+ foreach(i, list)
+ loop through list, assigning each list element to i. It is
+ important to note that i is a List *, not the data in the List
+ element. You need to use lfirst(i) to get at the data. Here is
+ a typical code snipped that loops through a List containing Var
+ *'s and processes each one:
+
+List *i, *list;
+
+ foreach(i, list)
+ {
+ Var *var = lfirst(i);
+
+ /* process var here */
+ }
+
+ lcons(node, list)
+ add node to the front of list, or create a new list with node
+ if list is NIL.
+
+ lappend(list, node)
+ add node to the end of list. This is more expensive that lcons.
+
+ nconc(list1, list2)
+ Concat list2 on to the end of list1.
+
+ length(list)
+ return the length of the list.
+
+ nth(i, list)
+ return the i'th element in list.
+
+ lconsi, ...
+ There are integer versions of these: lconsi, lappendi, nthi.
+ List's containing integers instead of Node pointers are used to
+ hold list of relation object id's and other integer quantities.
+
+ You can print nodes easily inside gdb. First, to disable output
+ truncation when you use the gdb print command:
+(gdb) set print elements 0
+
+ Instead of printing values in gdb format, you can use the next two
+ commands to print out List, Node, and structure contents in a verbose
+ format that is easier to understand. List's are unrolled into nodes,
+ and nodes are printed in detail. The first prints in a short format,
+ and the second in a long format:
+(gdb) call print(any_pointer)
+ (gdb) call pprint(any_pointer)
+
+ The output appears in the postmaster log file, or on your screen if
+ you are running a backend directly without a postmaster.
+
+ 2.4) I just added a field to a structure. What else should I do?
+
+ The structures passing around from the parser, rewrite, optimizer, and
+ executor require quite a bit of support. Most structures have support
+ routines in src/backend/nodes used to create, copy, read, and output
+ those structures. Make sure you add support for your new field to
+ these files. Find any other places the structure may need code for
+ your new field. mkid is helpful with this (see above).
+
+ 2.5) Why do we use palloc() and pfree() to allocate memory?
+
+ palloc() and pfree() are used in place of malloc() and free() because
+ we automatically free all memory allocated when a transaction
+ completes. This makes it easier to make sure we free memory that gets
+ allocated in one place, but only freed much later. There are several
+ contexts that memory can be allocated in, and this controls when the
+ allocated memory is automatically freed by the backend.
+
+ 2.6) What is elog()?
+
+ elog() is used to send messages to the front-end, and optionally
+ terminate the current query being processed. The first parameter is an
+ elog level of NOTICE, DEBUG, ERROR, or FATAL. NOTICE prints on the
+ user's terminal and the postmaster logs. DEBUG prints only in the
+ postmaster logs. ERROR prints in both places, and terminates the
+ current query, never returning from the call. FATAL terminates the
+ backend process. The remaining parameters of elog are a printf-style
+ set of parameters to print.
+
+ 2.7) What is CommandCounterIncrement()?
+
+ Normally, transactions can not see the rows they modify. This allows
+ UPDATE foo SET x = x + 1 to work correctly.
+
+ However, there are cases where a transactions needs to see rows
+ affected in previous parts of the transaction. This is accomplished
+ using a Command Counter. Incrementing the counter allows transactions
+ to be broken into pieces so each piece can see rows modified by
+ previous pieces. CommandCounterIncrement() increments the Command
+ Counter, creating a new part of the transaction.
diff --git a/doc/src/FAQ/FAQ_DEV.html b/doc/src/FAQ/FAQ_DEV.html
index 07f63e3a86a..2d00bdc5cad 100644
--- a/doc/src/FAQ/FAQ_DEV.html
+++ b/doc/src/FAQ/FAQ_DEV.html
@@ -27,39 +27,169 @@
<CENTER>
- <H2>Questions</H2>
+ <H2>General Questions</H2>
</CENTER>
- <A href="#1">1</A>) What tools are available for developers?<BR>
- <A href="#2">2</A>) What books are good for developers?<BR>
- <A href="#3">3</A>) Why do we use <I>palloc</I>() and
- <I>pfree</I>() to allocate memory?<BR>
- <A href="#4">4</A>) Why do we use <I>Node</I> and <I>List</I> to
- make data structures?<BR>
- <A href="#5">5</A>) How do I add a feature or fix a bug?<BR>
- <A href="#6">6</A>) How do I download/update the current source
+ <A href="#1.1">1.1</A>) How do I get involved in PostgreSQL
+ development?<BR>
+ <A href="#1.2">1.2</A>) How do I add a feature or fix a bug?<BR>
+ <A href="#1.3">1.3</A>) How do I download/update the current source
tree?<BR>
- <A href="#7">7</A>) How do I test my changes?<BR>
- <A href="#7">7</A>) I just added a field to a structure. What else
- should I do?<BR>
- <A href="#8">8</A>) Why are table, column, type, function, view
+ <A href="#1.4">1.4</A>) How do I test my changes?<BR>
+ <A href="#1.5">1.5</A>) What tools are available for developers?<BR>
+ <A href="#1.6">1.6</A>) What books are good for developers?<BR>
+ <A href="#1.7">1.7</A>) What is configure all about?<BR>
+ <A href="#1.8">1.8</A>) How do I add a new port?<BR>
+ <A href="#1.9">1.9</A>) Why don't we use threads in the backend?<BR>
+ <A href="#1.10">1.10</A>) How are RPM's packaged?<BR>
+ <A href="#1.11">1.11</A>) How are CVS branches handled?<BR>
+
+ <H2>Technical Questions</H2>
+ <A href="#2.1">2.1</A>) How do I efficiently access information in
+ tables from the backend code?<BR>
+ <A href="#2.2">2.2</A>) Why are table, column, type, function, view
names sometimes referenced as <I>Name</I> or <I>NameData,</I> and
sometimes as <I>char *?</I><BR>
- <A href="#9">9</A>) How do I efficiently access information in
- tables from the backend code?<BR>
- <A href="#10">10</A>) What is elog()?<BR>
- <A href="#11">11</A>) What is configure all about?<BR>
- <A href="#12">12</A>) How do I add a new port?<BR>
- <A href="#13">13</A>) What is CommandCounterIncrement()?<BR>
- <A href="#14">14</A>) Why don't we use threads in the backend?<BR>
- <A href="#15">15</A>) How are RPM's packaged?<BR>
- <A href="#16">16</A>) How are CVS branches handled?<BR>
- <A href="#17">17</A>) How do I get involved in PostgreSQL
- development?<BR>
+ <A href="#2.3">2.3</A>) Why do we use <I>Node</I> and <I>List</I> to
+ make data structures?<BR>
+ <A href="#2.4">2.4</A>) I just added a field to a structure. What else
+ should I do?<BR>
+ <A href="#2.5">2.5</A>) Why do we use <I>palloc</I>() and
+ <I>pfree</I>() to allocate memory?<BR>
+ <A href="#2.6">2.6</A>) What is elog()?<BR>
+ <A href="#2.7">2.7</A>) What is CommandCounterIncrement()?<BR>
<BR>
<HR>
- <H3><A name="1">1</A>) What tools are available for
+ <CENTER>
+ <H2>General Questions</H2>
+ </CENTER>
+
+ <H3><A name="1.1">1.1</A>) How go I get involved in PostgreSQL
+ development?</H3>
+
+ <P>This was written by Lamar Owen:</P>
+
+ <P>2001-06-22</P>
+
+ <B>What open source development process is used by the PostgreSQL
+ team?</B>
+
+ <P>Read HACKERS for six months (or a full release cycle, whichever
+ is longer). Really. HACKERS _is_the process. The process is not
+ well documented (AFAIK -- it may be somewhere that I am not aware
+ of) -- and it changes continually.</P>
+
+ <B>What development environment (OS, system, compilers, etc) is
+ required to develop code?</B>
+
+ <P><A href="developers.postgresql.org">Developers Corner</A> on the
+ website has links to this information. The distribution tarball
+ itself includes all the extra tools and documents that go beyond a
+ good Unix-like development environment. In general, a modern unix
+ with a modern gcc, GNU make or equivalent, autoconf (of a
+ particular version), and good working knowledge of those tools are
+ required.</P>
+
+ <B>What areas need support?</B>
+
+ <P>The TODO list.</P>
+
+ <P>You've made the first step, by finding and subscribing to
+ HACKERS. Once you find an area to look at in the TODO, and have
+ read the documentation on the internals, etc, then you check out a
+ current CVS,write what you are going to write (keeping your CVS
+ checkout up to date in the process), and make up a patch (as a
+ context diff only) and send to the PATCHES list, prefereably.</P>
+
+ <P>Discussion on the patch typically happens here. If the patch
+ adds a major feature, it would be a good idea to talk about it
+ first on the HACKERS list, in order to increase the chances of it
+ being accepted, as well as toavoid duplication of effort. Note that
+ experienced developers with a proven track record usually get the
+ big jobs -- for more than one reason. Also note that PostgreSQL is
+ highly portable -- nonportable code will likely be dismissed out of
+ hand.</P>
+
+ <P>Once your contributions get accepted, things move from there.
+ Typically, you would be added as a developer on the list on the
+ website when one of the other developers recommends it. Membership
+ on the steering committee is by invitation only, by the other
+ steering committee members, from what I have gathered watching
+ froma distance.</P>
+
+ <P>I make these statements from having watched the process for over
+ two years.</P>
+
+ <P>To see a good example of how one goes about this, search the
+ archives for the name 'Tom Lane' and see what his first post
+ consisted of, and where he took things. In particular, note that
+ this hasn't been _that_ long ago -- and his bugfixing and general
+ deep knowledge with this codebase is legendary. Take a few days to
+ read after him. And pay special attention to both the sheer
+ quantity as well as the painstaking quality of his work. Both are
+ in high demand.</P>
+
+ <H3><A name="1.2">1.2</A>) How do I add a feature or fix a bug?</H3>
+
+ <P>The source code is over 250,000 lines. Many problems/features
+ are isolated to one specific area of the code. Others require
+ knowledge of much of the source. If you are confused about where to
+ start, ask the hackers list, and they will be glad to assess the
+ complexity and give pointers on where to start.</P>
+
+ <P>Another thing to keep in mind is that many fixes and features
+ can be added with surprisingly little code. I often start by adding
+ code, then looking at other areas in the code where similar things
+ are done, and by the time I am finished, the patch is quite small
+ and compact.</P>
+
+ <P>When adding code, keep in mind that it should use the existing
+ facilities in the source, for performance reasons and for
+ simplicity. Often a review of existing code doing similar things is
+ helpful.</P>
+
+ <H3><A name="1.3">1.3</A>) How do I download/update the current source
+ tree?</H3>
+
+ <P>There are several ways to obtain the source tree. Occasional
+ developers can just get the most recent source tree snapshot from
+ ftp.postgresql.org. For regular developers, you can use CVS. CVS
+ allows you to download the source tree, then occasionally update
+ your copy of the source tree with any new changes. Using CVS, you
+ don't have to download the entire source each time, only the
+ changed files. Anonymous CVS does not allows developers to update
+ the remote source tree, though privileged developers can do this.
+ There is a CVS FAQ on our web site that describes how to use remote
+ CVS. You can also use CVSup, which has similarly functionality, and
+ is available from ftp.postgresql.org.</P>
+
+ <P>To update the source tree, there are two ways. You can generate
+ a patch against your current source tree, perhaps using the
+ make_diff tools mentioned above, and send them to the patches list.
+ They will be reviewed, and applied in a timely manner. If the patch
+ is major, and we are in beta testing, the developers may wait for
+ the final release before applying your patches.</P>
+
+ <P>For hard-core developers, Marc(scrappy@postgresql.org) will give
+ you a Unix shell account on postgresql.org, so you can use CVS to
+ update the main source tree, or you can ftp your files into your
+ account, patch, and cvs install the changes directly into the
+ source tree.</P>
+
+ <H3><A name="1.4">1.4</A>) How do I test my changes?</H3>
+
+ <P>First, use <I>psql</I> to make sure it is working as you expect.
+ Then run <I>src/test/regress</I> and get the output of
+ <I>src/test/regress/checkresults</I> with and without your changes,
+ to see that your patch does not change the regression test in
+ unexpected ways. This practice has saved me many times. The
+ regression tests test the code in ways I would never do, and has
+ caught many bugs in my patches. By finding the problems now, you
+ save yourself a lot of debugging later when things are broken, and
+ you can't figure out when it happened.</P>
+
+ <H3><A name="1.5">1.5</A>) What tools are available for
developers?</H3>
<P>Aside from the User documentation mentioned in the regular FAQ,
@@ -179,7 +309,7 @@
There is also a script called <I>unused_oids</I> in
<I>pgsql/src/include/catalog</I> that shows the unused oids.</P>
- <H3><A name="2">2</A>) What books are good for developers?</H3>
+ <H3><A name="1.6">1.6</A>) What books are good for developers?</H3>
<P>I have four good books, <I>An Introduction to Database
Systems,</I> by C.J. Date, Addison, Wesley, <I>A Guide to the SQL
@@ -192,207 +322,245 @@
on-line written by Jim Gray at <A href=
"http://www.benchmarkresources.com">http://www.benchmarkresources.com.</A></P>
- <H3><A name="3">3</A>) Why do we use <I>palloc</I>() and
- <I>pfree</I>() to allocate memory?</H3>
+ <H3><A name="1.7">1.7</A>) What is configure all about?</H3>
- <P><I>palloc()</I> and <I>pfree()</I> are used in place of malloc()
- and free() because we automatically free all memory allocated when
- a transaction completes. This makes it easier to make sure we free
- memory that gets allocated in one place, but only freed much later.
- There are several contexts that memory can be allocated in, and
- this controls when the allocated memory is automatically freed by
- the backend.</P>
+ <P>The files <I>configure</I> and <I>configure.in</I> are part of
+ the GNU <I>autoconf</I> package. Configure allows us to test for
+ various capabilities of the OS, and to set variables that can then
+ be tested in C programs and Makefiles. Autoconf is installed on the
+ PostgreSQL main server. To add options to configure, edit
+ <I>configure.in,</I> and then run <I>autoconf</I> to generate
+ <I>configure.</I></P>
- <H3><A name="4">4</A>) Why do we use <I>Node</I> and <I>List</I> to
- make data structures?</H3>
+ <P>When <I>configure</I> is run by the user, it tests various OS
+ capabilities, stores those in <I>config.status</I> and
+ <I>config.cache,</I> and modifies a list of <I>*.in</I> files. For
+ example, if there exists a <I>Makefile.in,</I> configure generates
+ a <I>Makefile</I> that contains substitutions for all @var@
+ parameters found by configure.</P>
- <P>We do this because this allows a consistent way to pass data
- inside the backend in a flexible way. Every node has a
- <I>NodeTag</I> which specifies what type of data is inside the
- Node. <I>Lists</I> are groups of <I>Nodes chained together as a
- forward-linked list.</I></P>
+ <P>When you need to edit files, make sure you don't waste time
+ modifying files generated by <I>configure.</I> Edit the <I>*.in</I>
+ file, and re-run <I>configure</I> to recreate the needed file. If
+ you run <I>make distclean</I> from the top-level source directory,
+ all files derived by configure are removed, so you see only the
+ file contained in the source distribution.</P>
- <P>Here are some of the <I>List</I> manipulation commands:</P>
+ <H3><A name="1.8">1.8</A>) How do I add a new port?</H3>
- <BLOCKQUOTE>
- <DL>
- <DT>lfirst(i)</DT>
+ <P>There are a variety of places that need to be modified to add a
+ new port. First, start in the <I>src/template</I> directory. Add an
+ appropriate entry for your OS. Also, use <I>src/config.guess</I> to
+ add your OS to <I>src/template/.similar.</I> You shouldn't match
+ the OS version exactly. The <I>configure</I> test will look for an
+ exact OS version number, and if not found, find a match without
+ version number. Edit <I>src/configure.in</I> to add your new OS.
+ (See configure item above.) You will need to run autoconf, or patch
+ <I>src/configure</I> too.</P>
- <DD>return the data at list element <I>i.</I></DD>
+ <P>Then, check <I>src/include/port</I> and add your new OS file,
+ with appropriate values. Hopefully, there is already locking code
+ in <I>src/include/storage/s_lock.h</I> for your CPU. There is also
+ a <I>src/makefiles</I> directory for port-specific Makefile
+ handling. There is a <I>backend/port</I> directory if you need
+ special files for your OS.</P>
- <DT>lnext(i)</DT>
+ <H3><A name="1.9">1.9</A>) Why don't we use threads in the
+ backend?</H3>
- <DD>return the next list element after <I>i.</I></DD>
+ <P>There are several reasons threads are not used:</P>
- <DT>foreach(i, list)</DT>
+ <UL>
+ <LI>Historically, threads were unsupported and buggy.</LI>
- <DD>
- loop through <I>list,</I> assigning each list element to
- <I>i.</I> It is important to note that <I>i</I> is a List *,
- not the data in the <I>List</I> element. You need to use
- <I>lfirst(i)</I> to get at the data. Here is a typical code
- snipped that loops through a List containing <I>Var *'s</I>
- and processes each one:
-<PRE>
-<CODE>List *i, *list;
-
- foreach(i, list)
- {
- Var *var = lfirst(i);
+ <LI>An error in one backend can corrupt other backends.</LI>
- /* process var here */
- }
-</CODE>
-</PRE>
- </DD>
+ <LI>Speed improvements using threads are small compared to the
+ remaining backend startup time.</LI>
- <DT>lcons(node, list)</DT>
+ <LI>The backend code would be more complex.</LI>
+ </UL>
- <DD>add <I>node</I> to the front of <I>list,</I> or create a
- new list with <I>node</I> if <I>list</I> is <I>NIL.</I></DD>
+ <H3><A name="1.10">1.10</A>) How are RPM's packaged?</H3>
- <DT>lappend(list, node)</DT>
+ <P>This was written by Lamar Owen:</P>
- <DD>add <I>node</I> to the end of <I>list.</I> This is more
- expensive that lcons.</DD>
+ <P>2001-05-03</P>
- <DT>nconc(list1, list2)</DT>
+ <P>As to how the RPMs are built -- to answer that question sanely
+ requires me to know how much experience you have with the whole RPM
+ paradigm. 'How is the RPM built?' is a multifaceted question. The
+ obvious simple answer is that I maintain:</P>
- <DD>Concat <I>list2</I> on to the end of <I>list1.</I></DD>
+ <OL>
+ <LI>A set of patches to make certain portions of the source tree
+ 'behave' in the different environment of the RPMset;</LI>
- <DT>length(list)</DT>
+ <LI>The initscript;</LI>
- <DD>return the length of the <I>list.</I></DD>
+ <LI>Any other ancilliary scripts and files;</LI>
- <DT>nth(i, list)</DT>
+ <LI>A README.rpm-dist document that tries to adequately document
+ both the differences between the RPM build and the WHY of the
+ differences, as well as useful RPM environment operations (like,
+ using syslog, upgrading, getting postmaster to start at OS boot,
+ etc);</LI>
- <DD>return the <I>i</I>'th element in <I>list.</I></DD>
+ <LI>The spec file that throws it all together. This is not a
+ trivial undertaking in a package of this size.</LI>
+ </OL>
- <DT>lconsi, ...</DT>
+ <P>I then download and build on as many different canonical
+ distributions as I can -- currently I am able to build on Red Hat
+ 6.2, 7.0, and 7.1 on my personal hardware. Occasionally I receive
+ opportunity from certain commercial enterprises such as Great
+ Bridge and PostgreSQL, Inc. to build on other distributions.</P>
- <DD>There are integer versions of these: <I>lconsi, lappendi,
- nthi.</I> <I>List's</I> containing integers instead of Node
- pointers are used to hold list of relation object id's and
- other integer quantities.</DD>
- </DL>
- </BLOCKQUOTE>
- You can print nodes easily inside <I>gdb.</I> First, to disable
- output truncation when you use the gdb <I>print</I> command:
-<PRE>
-<CODE>(gdb) set print elements 0
-</CODE>
-</PRE>
- Instead of printing values in gdb format, you can use the next two
- commands to print out List, Node, and structure contents in a
- verbose format that is easier to understand. List's are unrolled
- into nodes, and nodes are printed in detail. The first prints in a
- short format, and the second in a long format:
-<PRE>
-<CODE>(gdb) call print(any_pointer)
- (gdb) call pprint(any_pointer)
-</CODE>
-</PRE>
- The output appears in the postmaster log file, or on your screen if
- you are running a backend directly without a postmaster.
+ <P>I test the build by installing the resulting packages and
+ running the regression tests. Once the build passes these tests, I
+ upload to the postgresql.org ftp server and make a release
+ announcement. I am also responsible for maintaining the RPM
+ download area on the ftp site.</P>
- <H3><A name="5">5</A>) How do I add a feature or fix a bug?</H3>
+ <P>You'll notice I said 'canonical' distributions above. That
+ simply means that the machine is as stock 'out of the box' as
+ practical -- that is, everything (except select few programs) on
+ these boxen are installed by RPM; only official Red Hat released
+ RPMs are used (except in unusual circumstances involving software
+ that will not alter the build -- for example, installing a newer
+ non-RedHat version of the Dia diagramming package is OK --
+ installing Python 2.1 on the box that has Python 1.5.2 installed is
+ not, as that alters the PostgreSQL build). The RPM as uploaded is
+ built to as close to out-of-the-box pristine as is possible. Only
+ the standard released 'official to that release' compiler is used
+ -- and only the standard official kernel is used as well.</P>
- <P>The source code is over 250,000 lines. Many problems/features
- are isolated to one specific area of the code. Others require
- knowledge of much of the source. If you are confused about where to
- start, ask the hackers list, and they will be glad to assess the
- complexity and give pointers on where to start.</P>
+ <P>For a time I built on Mandrake for RedHat consumption -- no
+ more. Nonstandard RPM building systems are worse than useless.
+ Which is not to say that Mandrake is useless! By no means is
+ Mandrake useless -- unless you are building Red Hat RPMs -- and Red
+ Hat is useless if you're trying to build Mandrake or SuSE RPMs, for
+ that matter. But I would be foolish to use 'Lamar Owen's Super
+ Special RPM Blend Distro 0.1.2' to build for public consumption!
+ :-)</P>
- <P>Another thing to keep in mind is that many fixes and features
- can be added with surprisingly little code. I often start by adding
- code, then looking at other areas in the code where similar things
- are done, and by the time I am finished, the patch is quite small
- and compact.</P>
+ <P>I _do_ attempt to make the _source_ RPM compatible with as many
+ distributions as possible -- however, since I have limited
+ resources (as a volunteer RPM maintainer) I am limited as to the
+ amount of testing said build will get on other distributions,
+ architectures, or systems.</P>
- <P>When adding code, keep in mind that it should use the existing
- facilities in the source, for performance reasons and for
- simplicity. Often a review of existing code doing similar things is
- helpful.</P>
+ <P>And, while I understand people's desire to immediately upgrade
+ to the newest version, realize that I do this as a side interest --
+ I have a regular, full-time job as a broadcast
+ engineer/webmaster/sysadmin/Technical Director which occasionally
+ prevents me from making timely RPM releases. This happened during
+ the early part of the 7.1 beta cycle -- but I believe I was pretty
+ much on the ball for the Release Candidates and the final
+ release.</P>
- <H3><A name="6">6</A>) How do I download/update the current source
- tree?</H3>
+ <P>I am working towards a more open RPM distribution -- I would
+ dearly love to more fully document the process and put everything
+ into CVS -- once I figure out how I want to represent things such
+ as the spec file in a CVS form. It makes no sense to maintain a
+ changelog, for instance, in the spec file in CVS when CVS does a
+ better job of changelogs -- I will need to write a tool to generate
+ a real spec file from a CVS spec-source file that would add version
+ numbers, changelog entries, etc to the result before building the
+ RPM. IOW, I need to rethink the process -- and then go through the
+ motions of putting my long RPM history into CVS one version at a
+ time so that version history information isn't lost.</P>
- <P>There are several ways to obtain the source tree. Occasional
- developers can just get the most recent source tree snapshot from
- ftp.postgresql.org. For regular developers, you can use CVS. CVS
- allows you to download the source tree, then occasionally update
- your copy of the source tree with any new changes. Using CVS, you
- don't have to download the entire source each time, only the
- changed files. Anonymous CVS does not allows developers to update
- the remote source tree, though privileged developers can do this.
- There is a CVS FAQ on our web site that describes how to use remote
- CVS. You can also use CVSup, which has similarly functionality, and
- is available from ftp.postgresql.org.</P>
+ <P>As to why all these files aren't part of the source tree, well,
+ unless there was a large cry for it to happen, I don't believe it
+ should. PostgreSQL is very platform-agnostic -- and I like that.
+ Including the RPM stuff as part of the Official Tarball (TM) would,
+ IMHO, slant that agnostic stance in a negative way. But maybe I'm
+ too sensitive to that. I'm not opposed to doing that if that is the
+ consensus of the core group -- and that would be a sneaky way to
+ get the stuff into CVS :-). But if the core group isn't thrilled
+ with the idea (and my instinct says they're not likely to be), I am
+ opposed to the idea -- not to keep the stuff to myself, but to not
+ hinder the platform-neutral stance. IMHO, of course.</P>
- <P>To update the source tree, there are two ways. You can generate
- a patch against your current source tree, perhaps using the
- make_diff tools mentioned above, and send them to the patches list.
- They will be reviewed, and applied in a timely manner. If the patch
- is major, and we are in beta testing, the developers may wait for
- the final release before applying your patches.</P>
+ <P>Of course, there are many projects that DO include all the files
+ necessary to build RPMs from their Official Tarball (TM).</P>
- <P>For hard-core developers, Marc(scrappy@postgresql.org) will give
- you a Unix shell account on postgresql.org, so you can use CVS to
- update the main source tree, or you can ftp your files into your
- account, patch, and cvs install the changes directly into the
- source tree.</P>
+ <H3><A name="1.11">1.11</A>) How are CVS branches managed?</H3>
- <H3><A name="6">6</A>) How do I test my changes?</H3>
+ <P>This was written by Tom Lane:</P>
- <P>First, use <I>psql</I> to make sure it is working as you expect.
- Then run <I>src/test/regress</I> and get the output of
- <I>src/test/regress/checkresults</I> with and without your changes,
- to see that your patch does not change the regression test in
- unexpected ways. This practice has saved me many times. The
- regression tests test the code in ways I would never do, and has
- caught many bugs in my patches. By finding the problems now, you
- save yourself a lot of debugging later when things are broken, and
- you can't figure out when it happened.</P>
+ <P>2001-05-07</P>
- <H3><A name="7">7</A>) I just added a field to a structure. What
- else should I do?</H3>
+ <P>If you just do basic "cvs checkout", "cvs update", "cvs commit",
+ then you'll always be dealing with the HEAD version of the files in
+ CVS. That's what you want for development, but if you need to patch
+ past stable releases then you have to be able to access and update
+ the "branch" portions of our CVS repository. We normally fork off a
+ branch for a stable release just before starting the development
+ cycle for the next release.</P>
- <P>The structures passing around from the parser, rewrite,
- optimizer, and executor require quite a bit of support. Most
- structures have support routines in <I>src/backend/nodes</I> used
- to create, copy, read, and output those structures. Make sure you
- add support for your new field to these files. Find any other
- places the structure may need code for your new field. <I>mkid</I>
- is helpful with this (see above).</P>
+ <P>The first thing you have to know is the branch name for the
+ branch you are interested in getting at. To do this, look at some
+ long-lived file, say the top-level HISTORY file, with "cvs status
+ -v" to see what the branch names are. (Thanks to Ian Lance Taylor
+ for pointing out that this is the easiest way to do it.) Typical
+ branch names are:</P>
+<PRE>
+ REL7_1_STABLE
+ REL7_0_PATCHES
+ REL6_5_PATCHES
+</PRE>
- <H3><A name="8">8</A>) Why are table, column, type, function, view
- names sometimes referenced as <I>Name</I> or <I>NameData,</I> and
- sometimes as <I>char *?</I></H3>
+ <P>OK, so how do you do work on a branch? By far the best way is to
+ create a separate checkout tree for the branch and do your work in
+ that. Not only is that the easiest way to deal with CVS, but you
+ really need to have the whole past tree available anyway to test
+ your work. (And you *better* test your work. Never forget that
+ dot-releases tend to go out with very little beta testing --- so
+ whenever you commit an update to a stable branch, you'd better be
+ doubly sure that it's correct.)</P>
- <P>Table, column, type, function, and view names are stored in
- system tables in columns of type <I>Name.</I> Name is a
- fixed-length, null-terminated type of <I>NAMEDATALEN</I> bytes.
- (The default value for NAMEDATALEN is 32 bytes.)</P>
+ <P>Normally, to checkout the head branch, you just cd to the place
+ you want to contain the toplevel "pgsql" directory and say</P>
<PRE>
-<CODE>typedef struct nameData
- {
- char data[NAMEDATALEN];
- } NameData;
- typedef NameData *Name;
-</CODE>
+ cvs ... checkout pgsql
</PRE>
- Table, column, type, function, and view names that come into the
- backend via user queries are stored as variable-length,
- null-terminated character strings.
- <P>Many functions are called with both types of names, ie.
- <I>heap_open().</I> Because the Name type is null-terminated, it is
- safe to pass it to a function expecting a char *. Because there are
- many cases where on-disk names(Name) are compared to user-supplied
- names(char *), there are many cases where Name and char * are used
- interchangeably.</P>
+ <P>To get a past branch, you cd to whereever you want it and
+ say</P>
+<PRE>
+ cvs ... checkout -r BRANCHNAME pgsql
+</PRE>
+
+ <P>For example, just a couple days ago I did</P>
+<PRE>
+ mkdir ~postgres/REL7_1
+ cd ~postgres/REL7_1
+ cvs ... checkout -r REL7_1_STABLE pgsql
+</PRE>
+
+ <P>and now I have a maintenance copy of 7.1.*.</P>
+
+ <P>When you've done a checkout in this way, the branch name is
+ "sticky": CVS automatically knows that this directory tree is for
+ the branch, and whenever you do "cvs update" or "cvs commit" in
+ this tree, you'll fetch or store the latest version in the branch,
+ not the head version. Easy as can be.</P>
+
+ <P>So, if you have a patch that needs to apply to both the head and
+ a recent stable branch, you have to make the edits and do the
+ commit twice, once in your development tree and once in your stable
+ branch tree. This is kind of a pain, which is why we don't normally
+ fork the tree right away after a major release --- we wait for a
+ dot-release or two, so that we won't have to double-patch the first
+ wave of fixes.</P>
+
+ <CENTER>
+ <H2>Technical Questions</H2>
+ </CENTER>
- <H3><A name="9">9</A>) How do I efficiently access information in
+ <H3><A name="2.1">2.1</A>) How do I efficiently access information in
tables from the backend code?</H3>
<P>You first need to find the tuples(rows) you are interested in.
@@ -460,330 +628,172 @@
<I>ReleaseBuffer()</I>, in the <I>heap_fetch()</I> case. Or it may
be a palloc'ed tuple, that you must <I>pfree()</I> when finished.
- <H3><A name="10">10</A>) What is elog()?</H3>
+ <H3><A name="2.2">2.2</A>) Why are table, column, type, function, view
+ names sometimes referenced as <I>Name</I> or <I>NameData,</I> and
+ sometimes as <I>char *?</I></H3>
- <P><I>elog()</I> is used to send messages to the front-end, and
- optionally terminate the current query being processed. The first
- parameter is an elog level of <I>NOTICE,</I> <I>DEBUG,</I>
- <I>ERROR,</I> or <I>FATAL.</I> <I>NOTICE</I> prints on the user's
- terminal and the postmaster logs. <I>DEBUG</I> prints only in the
- postmaster logs. <I>ERROR</I> prints in both places, and terminates
- the current query, never returning from the call. <I>FATAL</I>
- terminates the backend process. The remaining parameters of
- <I>elog</I> are a <I>printf</I>-style set of parameters to
- print.</P>
+ <P>Table, column, type, function, and view names are stored in
+ system tables in columns of type <I>Name.</I> Name is a
+ fixed-length, null-terminated type of <I>NAMEDATALEN</I> bytes.
+ (The default value for NAMEDATALEN is 32 bytes.)</P>
+<PRE>
+<CODE>typedef struct nameData
+ {
+ char data[NAMEDATALEN];
+ } NameData;
+ typedef NameData *Name;
+</CODE>
+</PRE>
+ Table, column, type, function, and view names that come into the
+ backend via user queries are stored as variable-length,
+ null-terminated character strings.
- <H3><A name="11">11</A>) What is configure all about?</H3>
+ <P>Many functions are called with both types of names, ie.
+ <I>heap_open().</I> Because the Name type is null-terminated, it is
+ safe to pass it to a function expecting a char *. Because there are
+ many cases where on-disk names(Name) are compared to user-supplied
+ names(char *), there are many cases where Name and char * are used
+ interchangeably.</P>
- <P>The files <I>configure</I> and <I>configure.in</I> are part of
- the GNU <I>autoconf</I> package. Configure allows us to test for
- various capabilities of the OS, and to set variables that can then
- be tested in C programs and Makefiles. Autoconf is installed on the
- PostgreSQL main server. To add options to configure, edit
- <I>configure.in,</I> and then run <I>autoconf</I> to generate
- <I>configure.</I></P>
-
- <P>When <I>configure</I> is run by the user, it tests various OS
- capabilities, stores those in <I>config.status</I> and
- <I>config.cache,</I> and modifies a list of <I>*.in</I> files. For
- example, if there exists a <I>Makefile.in,</I> configure generates
- a <I>Makefile</I> that contains substitutions for all @var@
- parameters found by configure.</P>
-
- <P>When you need to edit files, make sure you don't waste time
- modifying files generated by <I>configure.</I> Edit the <I>*.in</I>
- file, and re-run <I>configure</I> to recreate the needed file. If
- you run <I>make distclean</I> from the top-level source directory,
- all files derived by configure are removed, so you see only the
- file contained in the source distribution.</P>
-
- <H3><A name="12">12</A>) How do I add a new port?</H3>
-
- <P>There are a variety of places that need to be modified to add a
- new port. First, start in the <I>src/template</I> directory. Add an
- appropriate entry for your OS. Also, use <I>src/config.guess</I> to
- add your OS to <I>src/template/.similar.</I> You shouldn't match
- the OS version exactly. The <I>configure</I> test will look for an
- exact OS version number, and if not found, find a match without
- version number. Edit <I>src/configure.in</I> to add your new OS.
- (See configure item above.) You will need to run autoconf, or patch
- <I>src/configure</I> too.</P>
-
- <P>Then, check <I>src/include/port</I> and add your new OS file,
- with appropriate values. Hopefully, there is already locking code
- in <I>src/include/storage/s_lock.h</I> for your CPU. There is also
- a <I>src/makefiles</I> directory for port-specific Makefile
- handling. There is a <I>backend/port</I> directory if you need
- special files for your OS.</P>
-
- <H3><A name="13">13</A>) What is CommandCounterIncrement()?</H3>
-
- <P>Normally, transactions can not see the rows they modify. This
- allows <CODE>UPDATE foo SET x = x + 1</CODE> to work correctly.</P>
-
- <P>However, there are cases where a transactions needs to see rows
- affected in previous parts of the transaction. This is accomplished
- using a Command Counter. Incrementing the counter allows
- transactions to be broken into pieces so each piece can see rows
- modified by previous pieces. <I>CommandCounterIncrement()</I>
- increments the Command Counter, creating a new part of the
- transaction.</P>
-
- <H3><A name="14">14</A>) Why don't we use threads in the
- backend?</H3>
-
- <P>There are several reasons threads are not used:</P>
-
- <UL>
- <LI>Historically, threads were unsupported and buggy.</LI>
-
- <LI>An error in one backend can corrupt other backends.</LI>
-
- <LI>Speed improvements using threads are small compared to the
- remaining backend startup time.</LI>
-
- <LI>The backend code would be more complex.</LI>
- </UL>
-
- <H3><A name="15">15</A>) How are RPM's packaged?</H3>
-
- <P>This was written by Lamar Owen:</P>
-
- <P>2001-05-03</P>
-
- <P>As to how the RPMs are built -- to answer that question sanely
- requires me to know how much experience you have with the whole RPM
- paradigm. 'How is the RPM built?' is a multifaceted question. The
- obvious simple answer is that I maintain:</P>
-
- <OL>
- <LI>A set of patches to make certain portions of the source tree
- 'behave' in the different environment of the RPMset;</LI>
+ <H3><A name="2.3">2.3</A>) Why do we use <I>Node</I> and <I>List</I> to
+ make data structures?</H3>
- <LI>The initscript;</LI>
+ <P>We do this because this allows a consistent way to pass data
+ inside the backend in a flexible way. Every node has a
+ <I>NodeTag</I> which specifies what type of data is inside the
+ Node. <I>Lists</I> are groups of <I>Nodes chained together as a
+ forward-linked list.</I></P>
- <LI>Any other ancilliary scripts and files;</LI>
+ <P>Here are some of the <I>List</I> manipulation commands:</P>
- <LI>A README.rpm-dist document that tries to adequately document
- both the differences between the RPM build and the WHY of the
- differences, as well as useful RPM environment operations (like,
- using syslog, upgrading, getting postmaster to start at OS boot,
- etc);</LI>
+ <BLOCKQUOTE>
+ <DL>
+ <DT>lfirst(i)</DT>
- <LI>The spec file that throws it all together. This is not a
- trivial undertaking in a package of this size.</LI>
- </OL>
+ <DD>return the data at list element <I>i.</I></DD>
- <P>I then download and build on as many different canonical
- distributions as I can -- currently I am able to build on Red Hat
- 6.2, 7.0, and 7.1 on my personal hardware. Occasionally I receive
- opportunity from certain commercial enterprises such as Great
- Bridge and PostgreSQL, Inc. to build on other distributions.</P>
+ <DT>lnext(i)</DT>
- <P>I test the build by installing the resulting packages and
- running the regression tests. Once the build passes these tests, I
- upload to the postgresql.org ftp server and make a release
- announcement. I am also responsible for maintaining the RPM
- download area on the ftp site.</P>
+ <DD>return the next list element after <I>i.</I></DD>
- <P>You'll notice I said 'canonical' distributions above. That
- simply means that the machine is as stock 'out of the box' as
- practical -- that is, everything (except select few programs) on
- these boxen are installed by RPM; only official Red Hat released
- RPMs are used (except in unusual circumstances involving software
- that will not alter the build -- for example, installing a newer
- non-RedHat version of the Dia diagramming package is OK --
- installing Python 2.1 on the box that has Python 1.5.2 installed is
- not, as that alters the PostgreSQL build). The RPM as uploaded is
- built to as close to out-of-the-box pristine as is possible. Only
- the standard released 'official to that release' compiler is used
- -- and only the standard official kernel is used as well.</P>
+ <DT>foreach(i, list)</DT>
- <P>For a time I built on Mandrake for RedHat consumption -- no
- more. Nonstandard RPM building systems are worse than useless.
- Which is not to say that Mandrake is useless! By no means is
- Mandrake useless -- unless you are building Red Hat RPMs -- and Red
- Hat is useless if you're trying to build Mandrake or SuSE RPMs, for
- that matter. But I would be foolish to use 'Lamar Owen's Super
- Special RPM Blend Distro 0.1.2' to build for public consumption!
- :-)</P>
+ <DD>
+ loop through <I>list,</I> assigning each list element to
+ <I>i.</I> It is important to note that <I>i</I> is a List *,
+ not the data in the <I>List</I> element. You need to use
+ <I>lfirst(i)</I> to get at the data. Here is a typical code
+ snipped that loops through a List containing <I>Var *'s</I>
+ and processes each one:
+<PRE>
+<CODE>List *i, *list;
+
+ foreach(i, list)
+ {
+ Var *var = lfirst(i);
- <P>I _do_ attempt to make the _source_ RPM compatible with as many
- distributions as possible -- however, since I have limited
- resources (as a volunteer RPM maintainer) I am limited as to the
- amount of testing said build will get on other distributions,
- architectures, or systems.</P>
+ /* process var here */
+ }
+</CODE>
+</PRE>
+ </DD>
- <P>And, while I understand people's desire to immediately upgrade
- to the newest version, realize that I do this as a side interest --
- I have a regular, full-time job as a broadcast
- engineer/webmaster/sysadmin/Technical Director which occasionally
- prevents me from making timely RPM releases. This happened during
- the early part of the 7.1 beta cycle -- but I believe I was pretty
- much on the ball for the Release Candidates and the final
- release.</P>
+ <DT>lcons(node, list)</DT>
- <P>I am working towards a more open RPM distribution -- I would
- dearly love to more fully document the process and put everything
- into CVS -- once I figure out how I want to represent things such
- as the spec file in a CVS form. It makes no sense to maintain a
- changelog, for instance, in the spec file in CVS when CVS does a
- better job of changelogs -- I will need to write a tool to generate
- a real spec file from a CVS spec-source file that would add version
- numbers, changelog entries, etc to the result before building the
- RPM. IOW, I need to rethink the process -- and then go through the
- motions of putting my long RPM history into CVS one version at a
- time so that version history information isn't lost.</P>
+ <DD>add <I>node</I> to the front of <I>list,</I> or create a
+ new list with <I>node</I> if <I>list</I> is <I>NIL.</I></DD>
- <P>As to why all these files aren't part of the source tree, well,
- unless there was a large cry for it to happen, I don't believe it
- should. PostgreSQL is very platform-agnostic -- and I like that.
- Including the RPM stuff as part of the Official Tarball (TM) would,
- IMHO, slant that agnostic stance in a negative way. But maybe I'm
- too sensitive to that. I'm not opposed to doing that if that is the
- consensus of the core group -- and that would be a sneaky way to
- get the stuff into CVS :-). But if the core group isn't thrilled
- with the idea (and my instinct says they're not likely to be), I am
- opposed to the idea -- not to keep the stuff to myself, but to not
- hinder the platform-neutral stance. IMHO, of course.</P>
+ <DT>lappend(list, node)</DT>
- <P>Of course, there are many projects that DO include all the files
- necessary to build RPMs from their Official Tarball (TM).</P>
+ <DD>add <I>node</I> to the end of <I>list.</I> This is more
+ expensive that lcons.</DD>
- <H3><A name="16">16</A>) How are CVS branches managed?</H3>
+ <DT>nconc(list1, list2)</DT>
- <P>This was written by Tom Lane:</P>
+ <DD>Concat <I>list2</I> on to the end of <I>list1.</I></DD>
- <P>2001-05-07</P>
+ <DT>length(list)</DT>
- <P>If you just do basic "cvs checkout", "cvs update", "cvs commit",
- then you'll always be dealing with the HEAD version of the files in
- CVS. That's what you want for development, but if you need to patch
- past stable releases then you have to be able to access and update
- the "branch" portions of our CVS repository. We normally fork off a
- branch for a stable release just before starting the development
- cycle for the next release.</P>
+ <DD>return the length of the <I>list.</I></DD>
- <P>The first thing you have to know is the branch name for the
- branch you are interested in getting at. To do this, look at some
- long-lived file, say the top-level HISTORY file, with "cvs status
- -v" to see what the branch names are. (Thanks to Ian Lance Taylor
- for pointing out that this is the easiest way to do it.) Typical
- branch names are:</P>
-<PRE>
- REL7_1_STABLE
- REL7_0_PATCHES
- REL6_5_PATCHES
-</PRE>
+ <DT>nth(i, list)</DT>
- <P>OK, so how do you do work on a branch? By far the best way is to
- create a separate checkout tree for the branch and do your work in
- that. Not only is that the easiest way to deal with CVS, but you
- really need to have the whole past tree available anyway to test
- your work. (And you *better* test your work. Never forget that
- dot-releases tend to go out with very little beta testing --- so
- whenever you commit an update to a stable branch, you'd better be
- doubly sure that it's correct.)</P>
+ <DD>return the <I>i</I>'th element in <I>list.</I></DD>
- <P>Normally, to checkout the head branch, you just cd to the place
- you want to contain the toplevel "pgsql" directory and say</P>
-<PRE>
- cvs ... checkout pgsql
-</PRE>
+ <DT>lconsi, ...</DT>
- <P>To get a past branch, you cd to whereever you want it and
- say</P>
+ <DD>There are integer versions of these: <I>lconsi, lappendi,
+ nthi.</I> <I>List's</I> containing integers instead of Node
+ pointers are used to hold list of relation object id's and
+ other integer quantities.</DD>
+ </DL>
+ </BLOCKQUOTE>
+ You can print nodes easily inside <I>gdb.</I> First, to disable
+ output truncation when you use the gdb <I>print</I> command:
<PRE>
- cvs ... checkout -r BRANCHNAME pgsql
+<CODE>(gdb) set print elements 0
+</CODE>
</PRE>
-
- <P>For example, just a couple days ago I did</P>
+ Instead of printing values in gdb format, you can use the next two
+ commands to print out List, Node, and structure contents in a
+ verbose format that is easier to understand. List's are unrolled
+ into nodes, and nodes are printed in detail. The first prints in a
+ short format, and the second in a long format:
<PRE>
- mkdir ~postgres/REL7_1
- cd ~postgres/REL7_1
- cvs ... checkout -r REL7_1_STABLE pgsql
+<CODE>(gdb) call print(any_pointer)
+ (gdb) call pprint(any_pointer)
+</CODE>
</PRE>
+ The output appears in the postmaster log file, or on your screen if
+ you are running a backend directly without a postmaster.
- <P>and now I have a maintenance copy of 7.1.*.</P>
-
- <P>When you've done a checkout in this way, the branch name is
- "sticky": CVS automatically knows that this directory tree is for
- the branch, and whenever you do "cvs update" or "cvs commit" in
- this tree, you'll fetch or store the latest version in the branch,
- not the head version. Easy as can be.</P>
-
- <P>So, if you have a patch that needs to apply to both the head and
- a recent stable branch, you have to make the edits and do the
- commit twice, once in your development tree and once in your stable
- branch tree. This is kind of a pain, which is why we don't normally
- fork the tree right away after a major release --- we wait for a
- dot-release or two, so that we won't have to double-patch the first
- wave of fixes.</P>
-
- <H3><A name="17">17</A>) How go I get involved in PostgreSQL
- development?</H3>
-
- <P>This was written by Lamar Owen:</P>
-
- <P>2001-06-22</P>
-
- <B>What open source development process is used by the PostgreSQL
- team?</B>
-
- <P>Read HACKERS for six months (or a full release cycle, whichever
- is longer). Really. HACKERS _is_the process. The process is not
- well documented (AFAIK -- it may be somewhere that I am not aware
- of) -- and it changes continually.</P>
+ <H3><A name="2.4">2.4</A>) I just added a field to a structure. What
+ else should I do?</H3>
- <B>What development environment (OS, system, compilers, etc) is
- required to develop code?</B>
+ <P>The structures passing around from the parser, rewrite,
+ optimizer, and executor require quite a bit of support. Most
+ structures have support routines in <I>src/backend/nodes</I> used
+ to create, copy, read, and output those structures. Make sure you
+ add support for your new field to these files. Find any other
+ places the structure may need code for your new field. <I>mkid</I>
+ is helpful with this (see above).</P>
- <P><A href="developers.postgresql.org">Developers Corner</A> on the
- website has links to this information. The distribution tarball
- itself includes all the extra tools and documents that go beyond a
- good Unix-like development environment. In general, a modern unix
- with a modern gcc, GNU make or equivalent, autoconf (of a
- particular version), and good working knowledge of those tools are
- required.</P>
+ <H3><A name="2.5">2.5</A>) Why do we use <I>palloc</I>() and
+ <I>pfree</I>() to allocate memory?</H3>
- <B>What areas need support?</B>
+ <P><I>palloc()</I> and <I>pfree()</I> are used in place of malloc()
+ and free() because we automatically free all memory allocated when
+ a transaction completes. This makes it easier to make sure we free
+ memory that gets allocated in one place, but only freed much later.
+ There are several contexts that memory can be allocated in, and
+ this controls when the allocated memory is automatically freed by
+ the backend.</P>
- <P>The TODO list.</P>
+ <H3><A name="2.6">2.6</A>) What is elog()?</H3>
- <P>You've made the first step, by finding and subscribing to
- HACKERS. Once you find an area to look at in the TODO, and have
- read the documentation on the internals, etc, then you check out a
- current CVS,write what you are going to write (keeping your CVS
- checkout up to date in the process), and make up a patch (as a
- context diff only) and send to the PATCHES list, prefereably.</P>
+ <P><I>elog()</I> is used to send messages to the front-end, and
+ optionally terminate the current query being processed. The first
+ parameter is an elog level of <I>NOTICE,</I> <I>DEBUG,</I>
+ <I>ERROR,</I> or <I>FATAL.</I> <I>NOTICE</I> prints on the user's
+ terminal and the postmaster logs. <I>DEBUG</I> prints only in the
+ postmaster logs. <I>ERROR</I> prints in both places, and terminates
+ the current query, never returning from the call. <I>FATAL</I>
+ terminates the backend process. The remaining parameters of
+ <I>elog</I> are a <I>printf</I>-style set of parameters to
+ print.</P>
- <P>Discussion on the patch typically happens here. If the patch
- adds a major feature, it would be a good idea to talk about it
- first on the HACKERS list, in order to increase the chances of it
- being accepted, as well as toavoid duplication of effort. Note that
- experienced developers with a proven track record usually get the
- big jobs -- for more than one reason. Also note that PostgreSQL is
- highly portable -- nonportable code will likely be dismissed out of
- hand.</P>
+ <H3><A name="2.7">2.7</A>) What is CommandCounterIncrement()?</H3>
- <P>Once your contributions get accepted, things move from there.
- Typically, you would be added as a developer on the list on the
- website when one of the other developers recommends it. Membership
- on the steering committee is by invitation only, by the other
- steering committee members, from what I have gathered watching
- froma distance.</P>
+ <P>Normally, transactions can not see the rows they modify. This
+ allows <CODE>UPDATE foo SET x = x + 1</CODE> to work correctly.</P>
- <P>I make these statements from having watched the process for over
- two years.</P>
+ <P>However, there are cases where a transactions needs to see rows
+ affected in previous parts of the transaction. This is accomplished
+ using a Command Counter. Incrementing the counter allows
+ transactions to be broken into pieces so each piece can see rows
+ modified by previous pieces. <I>CommandCounterIncrement()</I>
+ increments the Command Counter, creating a new part of the
+ transaction.</P>
- <P>To see a good example of how one goes about this, search the
- archives for the name 'Tom Lane' and see what his first post
- consisted of, and where he took things. In particular, note that
- this hasn't been _that_ long ago -- and his bugfixing and general
- deep knowledge with this codebase is legendary. Take a few days to
- read after him. And pay special attention to both the sheer
- quantity as well as the painstaking quality of his work. Both are
- in high demand.</P>
</BODY>
</HTML>
-
--
GitLab