Skip to content
Snippets Groups Projects
Commit 34d59572 authored by Bruce Momjian's avatar Bruce Momjian
Browse files

update

parent 2584029e
No related branches found
No related tags found
No related merge requests found
Hide whitespace changes
Inline Side-by-side
src/tools/backend/index.html
+ 25
− 22
View file @ 34d59572
<HTML>
<HEAD>
<TITLE>PostgreSQL Backend Flowchart</TITLE>
<TITLE>How PostgreSQL Processes a Query</TITLE>
</HEAD>
<BODY BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#FF0000" VLINK="#A00000" ALINK="#0000FF">
<H1 ALIGN=CENTER>
PostgreSQL Backend Flowchart
How PostgreSQL Processes a Query
</H1>
<H2 ALIGN=CENTER>
by Bruce Momjian
</H2>
<P>
A query come into the backend via data packets coming in through TCP/IP
and Unix Domain sockets. It is loaded into a string, and passed to
A query comes to the backend via data packets arriving through TCP/IP
or Unix Domain sockets. It is loaded into a string, and passed to
the
<A HREF="../../backend/parser">parser,</A> where the lexical scanner,
<A HREF="../../backend/parser/scan.l">scan.l,</A>
breaks the query up into tokens(words). The parser
uses
<A HREF="../../backend/parser/gram.y">gram.y</A> and the tokens to
identify the query type, and load the proper query-specific
structure, like
<A HREF="../../include/nodes/parsenodes.h">CreateStmt or SelectStmt.</A>
identify the query type, and load the proper query-specific structure,
like <A HREF="../../include/nodes/parsenodes.h">CreateStmt</A> or <A
HREF="../../include/nodes/parsenodes.h">SelectStmt.</A>
<P>
The query is then identified as a <I>Utility</I> function or a more
complex query. A <I>Utility</I> query is processed by a
query-specific function in <A HREF="../../backend/commands">
commands.</A> A complex query, like <CODE>SELECT, UPDATE,</CODE> and
The query is then identified as a <I>Utility</I> query or a more complex
query. A <I>Utility</I> query is processed by a query-specific function
in <A HREF="../../backend/commands"> commands.</A> A complex query, like
<CODE>SELECT, UPDATE,</CODE> and
<CODE>DELETE</CODE> requires much more handling.
<P>
The parser takes a complex query, and creates a
......@@ -37,7 +37,7 @@ Each table referenced in the query is represented by a <A
HREF="../../include/nodes/parsenodes.h"> RangeTableEntry,</A> and they
are linked together to form the <I>range table</I> of the query, which is
generated by <A HREF="../../backend/parser/parse_clause.c">
makeRangeTable().</A> Query.rtable holds the queries range table.
makeRangeTable().</A> Query.rtable holds the query's range table.
<P>
Certain queries, like <CODE>SELECT,</CODE> return columns of data. Other
queries, like <CODE>INSERT</CODE> and <CODE>UPDATE,</CODE> specify the columns
......@@ -48,7 +48,7 @@ target list is stored in Query.targetList, which is generated by
<A HREF="../../backend/parser/parse_target.c">transformTargetList().</A>
<P>
Other query elements, like aggregates(<CODE>SUM()</CODE>), <CODE>GROUP BY,</CODE>
<CODE>ORDER BY</CODE> are also stored in their own Query fields.
and <CODE>ORDER BY</CODE> are also stored in their own Query fields.
<P>
The next step is for the Query to be modified by any <CODE>VIEWS</CODE> or
<CODE>RULES</CODE> that may apply to the query. This is performed by the <A
......@@ -69,21 +69,22 @@ returned to the client.
There are many other modules that support this basic functionality.
They can be accessed by clicking on the flowchart.
<P>
Another area of interest is the shared memory area, containing table
data/index blocks, locks, backend information, and lookup tables for
these structures:
Another area of interest is the shared memory area, which contains data
accessable to all backends. It has table recently used data/index
blocks, locks, backend information, and lookup tables for these
structures:
<UL>
<LI>ShmemIndex - lookup shared memory addresses using structure names
<LI><A HREF="../../include/storage/buf_internals.h">Buffer
Descriptors</A> - control header for buffer cache block
<LI><A HREF="../../include/storage/buf_internals.h">Buffer Blocks</A> -
Descriptor</A> - control header for buffer cache block
<LI><A HREF="../../include/storage/buf_internals.h">Buffer Block</A> -
data/index buffer cache block
<LI>Shared Buf Lookup Table - lookup of buffer cache block address using
<LI>Shared Buffer Lookup Table - lookup of buffer cache block addresses using
table name and block number(<A HREF="../../include/storage/buf_internals.h">
BufferTag</A>)
<LI>MultiLevelLockTable (ctl) - <A
HREF="../../include/storage/lock.h">LOCKCTL</A> control structure for
each locking method. Currently, only multi-level locking is used.
<LI>MultiLevelLockTable (ctl) - control structure for
each locking method. Currently, only multi-level locking is used(<A
HREF="../../include/storage/lock.h">LOCKMETHODCTL</A>).
<LI>MultiLevelLockTable (lock hash) - the <A
HREF="../../include/storage/lock.h">LOCK</A> structure, looked up using
relation, database object ids(<A
......@@ -105,7 +106,9 @@ Each data structure is created by calling <A
HREF="../../backend/storage/ipc/shmem.c">ShmemInitStruct(),</A> and
the lookups are created by
<A HREF="../../backend/storage/ipc/shmem.c">ShmemInitHash().</A>
<P>
<HR>
<P>
<CENTER>
<EM><BIG>
Click on an item to see more detail or
......
0% or .
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment