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diff --git a/src/tools/backend/index.html b/src/tools/backend/index.html deleted file mode 100644 index eb4978bfe04..00000000000 --- a/src/tools/backend/index.html +++ /dev/null @@ -1,155 +0,0 @@ -<!-- src/tools/backend/index.html --> -<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" - "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> -<html xmlns="http://www.w3.org/1999/xhtml"> -<head> -<meta name="generator" -content="HTML Tidy for BSD/OS (vers 1st July 2002), see www.w3.org" /> -<title>How PostgreSQL Processes a Query</title> -</head> -<body bgcolor="#FFFFFF" text="#000000" link="#FF0000" -vlink="#A00000" alink="#0000FF"> -<h1>How PostgreSQL Processes a Query</h1> - -<h2>by Bruce Momjian</h2> - -<center> -<h3><i>Click on an item</i> to see more detail or look at the full -<a href="backend_dirs.html">index.</a></h3> - -<p><img src="flow.gif" usemap="#flowmap" alt="flowchart" /> - -<map name="flowmap" id="flowmap"> -<area coords="45, 0, 175, 30" href="backend_dirs.html#main" alt="main" /> -<area coords="255, 35, 380, 65" href="backend_dirs.html#libpq" alt="libpq" /> -<area coords="45, 65, 175, 95" href="backend_dirs.html#postmaster" alt="postmaster" /> -<area coords="45, 130, 175, 160" href="backend_dirs.html#tcop" alt="tcop" /> -<area coords="250, 130, 380, 160" href="backend_dirs.html#tcop" alt="tcop" /> -<area coords="45, 205, 175, 240" href="backend_dirs.html#parser" alt="parser" /> -<area coords="45, 270, 175, 300" href="backend_dirs.html#tcop" alt="tcop" /> -<area coords="255, 270, 380, 300" href="backend_dirs.html#commands" alt="commands" /> -<area coords="45, 335, 175, 365" href="backend_dirs.html#rewrite" alt="rewrite" /> -<area coords="45, 400, 175, 430" href="backend_dirs.html#optimizer_path" alt="path" /> -<area coords="45, 460, 175, 490" href="backend_dirs.html#optimizer_plan" alt="plan" /> -<area coords="45, 525, 175, 555" href="backend_dirs.html#executor" alt="executor" /> -<area coords="0, 640, 130, 675" href="backend_dirs.html#utils" alt="utils" /> -<area coords="175, 640, 300, 675" href="backend_dirs.html#catalog" alt="catalog" /> -<area coords="330, 640, 475, 675" href="backend_dirs.html#storage" alt="storage" /> -<area coords="75, 700, 210, 735" href="backend_dirs.html#access" alt="access" /> -<area coords="255, 705, 380, 735" href="backend_dirs.html#nodes" alt="nodes" /> -</map> -</center> - -<br /> - -<p>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</a> or <a -href="../../include/nodes/parsenodes.h">SelectStmt.</a></p> - -<p>The statement is then identified as complex (<i>SELECT / INSERT / -UPDATE / DELETE</i>) or a simple, e.g <i> CREATE USER, ANALYZE, </i>, -etc. Simple utility commands are processed by statement-specific -functions in <a href="../../backend/commands">backend/commands.</a> -Complex statements require more handling.</p> - -<p>The parser takes a complex query, and creates a <a -href="../../include/nodes/parsenodes.h">Query</a> structure that -contains all the elements used by complex queries. Query.qual holds -the <i>WHERE</i> clause qualification, which is filled in by <a -href="../../backend/parser/parse_clause.c">transformWhereClause().</a> -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">transformFromClause().</a> -Query.rtable holds the query's range table.</p> - -<p>Certain queries, like <i>SELECT,</i> return columns of data. -Other queries, like <i>INSERT</i> and <i>UPDATE,</i> specify the -columns modified by the query. These column references are -converted to <a -href="../../include/nodes/primnodes.h">TargetEntry</a> entries, -which are linked together to make up the <i>target list</i> of the -query. The target list is stored in Query.targetList, which is -generated by <a -href="../../backend/parser/parse_target.c">transformTargetList().</a></p> - -<p>Other query elements, like aggregates(<i>SUM()</i>), <i>GROUP -BY,</i> and <i>ORDER BY</i> are also stored in their own Query -fields.</p> - -<p>The next step is for the Query to be modified by any -<i>VIEWS</i> or <i>RULES</i> that may apply to the query. This is -performed by the <a href="../../backend/rewrite">rewrite</a> -system.</p> - -<p>The <a href="../../backend/optimizer">optimizer</a> takes the -Query structure and generates an optimal <a -href="../../include/nodes/plannodes.h">Plan,</a> which contains the -operations to be performed to execute the query. The <a -href="../../backend/optimizer/path">path</a> module determines the -best table join order and join type of each table in the -RangeTable, using Query.qual(<i>WHERE</i> clause) to consider -optimal index usage.</p> - -<p>The Plan is then passed to the <a -href="../../backend/executor">executor</a> for execution, and the -result returned to the client. The Plan is actually as set of nodes, -arranged in a tree structure with a top-level node, and various -sub-nodes as children.</p> - -<p>There are many other modules that support this basic -functionality. They can be accessed by clicking on the -flowchart.</p> - -<hr /> -<p>Another area of interest is the shared memory area, which -contains data accessible to all backends. It has recently used -data/index blocks, locks, backend process information, and lookup -tables for these structures:</p> - -<ul> -<li>ShmemIndex - lookup shared memory addresses using structure -names</li> - -<li><a href="../../include/storage/buf_internals.h">Buffer -Descriptor</a> - control header for buffer cache block</li> - -<li><a href="../../include/storage/buf_internals.h">Buffer -Block</a> - data/index buffer cache block</li> - -<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> - -<li>Lock Manager Tables (lock hash) - the <a -href="../../include/storage/lock.h">LOCK</a> structure, looked up -using a <a href="../../include/storage/lock.h">LOCKTAG</a>. -A LOCK structure exists for each lockable object that is currently -locked by any backend. Also, there is a subsidiary <a -href="../../include/storage/lock.h">PROCLOCK</a> structure for each -backend currently interested in a given LOCK</li> - -<li><a href="../../include/storage/proc.h">PGPROC Structures</a> - -information about each backend, including locks held/waiting</li> -</ul> - -<p>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 /> -<small>Maintainer: Bruce Momjian (<a -href="mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</a>)<br /> - -Last updated: Fri May 6 14:22:27 EDT 2005</small> -</body> -</html> |