Remove src/tool/backend, now that the content is on the web site and wiki.
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Bruce Momjian
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src/tools/backend/README
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Just point your browser at the index.html file, and click on the
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flowchart to see the description and source code.
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
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"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<meta name="generator"
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content="HTML Tidy for BSD/OS (vers 1st July 2002), see www.w3.org" />
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<title>PostgreSQL Backend Directories</title>
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</head>
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<body bgcolor="#FFFFFF" text="#000000" link="#FF0000"
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vlink="#A00000" alink="#0000FF">
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<h1>PostgreSQL Backend Directories</h1>
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<h2>by Bruce Momjian</h2>
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<hr />
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<p><em>Click on any of the section headings to see the source code
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for that section.</em></p>
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<h2><a id="bootstrap" name="bootstrap"></a> <a
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href="../../backend/bootstrap">bootstrap</a> - creates initial
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template database via initdb</h2>
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<p>Because PostgreSQL requires access to system tables for almost
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every operation, getting those system tables in place is a problem.
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You can't just create the tables and insert data into them in the
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normal way, because table creation and insertion requires the
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tables to already exist. This code <i>jams</i> the data directly
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into tables using a special syntax used only by the bootstrap
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procedure.</p>
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<h2><a id="main" name="main"></a> <a
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href="../../backend/main">main</a> - passes control to postmaster
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or postgres</h2>
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<p>This checks the process name(argv[0]) and various flags, and
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passes control to the postmaster or postgres backend code.</p>
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<h2><a id="postmaster" name="postmaster"></a> <a
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href="../../backend/postmaster">postmaster</a> - controls postgres
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server startup/termination</h2>
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<p>This creates shared memory, and then goes into a loop waiting
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for connection requests. When a connection request arrives, a
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<i>postgres</i> backend is started, and the connection is passed to
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it.</p>
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<h2><a id="libpq" name="libpq"></a> <a
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href="../../backend/libpq">libpq</a> - backend libpq library
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routines</h2>
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<p>This handles communication to the client processes.</p>
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<h2><a id="tcop" name="tcop"></a> <a
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href="../../backend/tcop">tcop</a> - traffic cop, dispatches
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request to proper module</h2>
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<p>This contains the <i>postgres</i> backend main handler, as well
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as the code that makes calls to the parser, optimizer, executor,
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and <i>/commands</i> functions.</p>
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<h2><a id="parser" name="parser"></a> <a
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href="../../backend/parser">parser</a> - converts SQL query to
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query tree</h2>
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<p>This converts SQL queries coming from <i>libpq</i> into
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command-specific structures to be used the optimizer/executor,
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or <i>/commands</i> routines. The SQL is lexically analyzed into
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keywords, identifiers, and constants, and passed to the parser. The
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parser creates command-specific structures to hold the elements of
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the query. The command-specific structures are then broken apart,
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checked, and passed to <i>/commands</i> processing routines, or
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converted into <i>Lists</i> of <i>Nodes</i> to be handled by the
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optimizer and executor.</p>
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<h2><a id="rewrite" name="rewrite"></a> <a
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href="../../backend/rewrite">rewrite</a> - rule and views
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support</h2>
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<h2><a id="optimizer" name="optimizer"></a> <a
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href="../../backend/optimizer">optimizer</a> - creates path and
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plan</h2>
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<p>This uses the parser output to generate an optimal plan for the
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executor.</p>
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<h3><a id="optimizer_path" name="optimizer_path"></a> <a
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href="../../backend/optimizer/path">optimizer/path</a> - creates
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path from parser output</h3>
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<p>This takes the parser query output, and generates all possible
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methods of executing the request. It examines table join order,
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<i>where</i> clause restrictions, and optimizer table statistics to
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evaluate each possible execution method, and assigns a cost to
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each.</p>
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<h3><a id="optimizer_geqo" name="optimizer_geqo"></a> <a
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href="../../backend/optimizer/geqo">optimizer/geqo</a> - genetic
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query optimizer</h3>
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<p><i>optimizer/path</i> evaluates all possible ways to join the
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requested tables. When the number of tables becomes great, the
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number of tests made becomes great too. The Genetic Query Optimizer
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considers each table separately, then figures the most optimal
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order to perform the join. For a few tables, this method takes
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longer, but for a large number of tables, it is faster. There is an
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option to control when this feature is used.</p>
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<h3><a id="optimizer_plan" name="optimizer_plan"></a> <a
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href="../../backend/optimizer/plan">optimizer/plan</a> - optimizes
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path output</h3>
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<p>This takes the <i>optimizer/path</i> output, chooses the path
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with the least cost, and creates a plan for the executor.</p>
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<h3><a id="optimizer_prep" name="optimizer_prep"></a> <a
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href="../../backend/optimizer/prep">optimizer/prep</a> - handle
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special plan cases</h3>
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<p>This does special plan processing.</p>
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<h3><a id="optimizer_util" name="optimizer_util"></a> <a
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href="../../backend/optimizer/util">optimizer/util</a> - optimizer
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support routines</h3>
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<p>This contains support routines used by other parts of the
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optimizer.</p>
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<h2><a id="executor" name="executor"></a> <a
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href="../../backend/executor">executor</a> - executes complex node
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plans from optimizer</h2>
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<p>This handles <i>select, insert, update,</i> and <i>delete</i>
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statements. The operations required to handle these statement types
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include heap scans, index scans, sorting, joining tables, grouping,
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aggregates, and uniqueness.</p>
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<h2><a id="commands" name="commands"></a> <a
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href="../../backend/commands">commands</a> - commands that do not
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require the executor</h2>
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<p>These process SQL commands that do not require complex handling.
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It includes <i>vacuum, copy, alter, create table, create type,</i>
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and many others. The code is called with the structures generated
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by the parser. Most of the routines do some processing, then call
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lower-level functions in the catalog directory to do the actual
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work.</p>
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<h2><a id="catalog" name="catalog"></a> <a
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href="../../backend/catalog">catalog</a> - system catalog
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manipulation</h2>
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<p>This contains functions that manipulate the system tables or
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catalogs. Table, index, procedure, operator, type, and aggregate
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creation and manipulation routines are here. These are low-level
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routines, and are usually called by upper routines that pre-format
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user requests into a predefined format.</p>
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<h2><a id="storage" name="storage"></a> <a
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href="../../backend/storage">storage</a> - manages various storage
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systems</h2>
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<p>These allow uniform resource access by the backend.<br />
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<br />
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<a id="storage_buffer" name="storage_buffer"></a> <a
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href="../../backend/storage/buffer">storage/buffer</a> - shared
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buffer pool manager<br />
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<a id="storage_file" name="storage_file"></a> <a
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href="../../backend/storage/file">storage/file</a> - file
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manager<br />
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<a id="storage_freespace" name="storage_freespace"></a> <a
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href="../../backend/storage/freespace">storage/freespace</a> - free
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space map<br />
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<a id="storage_ipc" name="storage_ipc"></a> <a
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href="../../backend/storage/ipc">storage/ipc</a> - semaphores and
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shared memory<br />
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<a id="storage_large_object" name="storage_large_object"></a> <a
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href="../../backend/storage/large_object">storage/large_object</a>
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- large objects<br />
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<a id="storage_lmgr" name="storage_lmgr"></a> <a
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href="../../backend/storage/lmgr">storage/lmgr</a> - lock
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manager<br />
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<a id="storage_page" name="storage_page"></a> <a
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href="../../backend/storage/page">storage/page</a> - page
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manager<br />
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<a id="storage_smgr" name="storage_smgr"></a> <a
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href="../../backend/storage/smgr">storage/smgr</a> - storage/disk
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manager<br />
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<br />
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</p>
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<h2><a id="access" name="access"></a> <a
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href="../../backend/access">access</a> - various data access
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methods</h2>
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<p>These control the way data is accessed in heap, indexes, and
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transactions.<br />
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<br />
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<a id="access_common" name="access_common"></a> <a
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href="../../backend/access/common">access/common</a> - common
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access routines<br />
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<a id="access_gist" name="access_gist"></a> <a
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href="../../backend/access/gist">access/gist</a> - easy-to-define
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access method system<br />
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<a id="access_hash" name="access_hash"></a> <a
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href="../../backend/access/hash">access/hash</a> - hash<br />
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<a id="access_heap" name="access_heap"></a> <a
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href="../../backend/access/heap">access/heap</a> - heap is use to
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store data rows<br />
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<a id="access_index" name="access_index"></a> <a
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href="../../backend/access/index">access/index</a> - used by all
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index types<br />
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<a id="access_nbtree" name="access_nbtree"></a> <a
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href="../../backend/access/nbtree">access/nbtree</a> - Lehman and
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Yao's btree management algorithm<br />
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<a id="access_transam" name="access_transam"></a> <a
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href="../../backend/access/transam">access/transam</a> -
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transaction manager (BEGIN/ABORT/COMMIT)<br />
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<br />
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</p>
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<h2><a id="nodes" name="nodes"></a> <a
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href="../../backend/nodes">nodes</a> - creation/manipulation of
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nodes and lists</h2>
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<p>PostgreSQL stores information about SQL queries in structures
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called nodes. <i>Nodes</i> are generic containers that have a
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<i>type</i> field and then a type-specific data section. Nodes are
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usually placed in <i>Lists.</i> A <i>List</i> is container with an
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<i>elem</i> element, and a <i>next</i> field that points to the
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next <i>List.</i> These <i>List</i> structures are chained together
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in a forward linked list. In this way, a chain of <i>List</i> s can
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contain an unlimited number of <i>Node</i> elements, and each
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<i>Node</i> can contain any data type. These are used extensively
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in the parser, optimizer, and executor to store requests and
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data.</p>
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<h2><a id="utils" name="utils"></a> <a
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href="../../backend/utils">utils</a> - support routines</h2>
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<h3><a id="utils_adt" name="utils_adt"></a> <a
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href="../../backend/utils/adt">utils/adt</a> - built-in data type
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routines</h3>
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<p>This contains all the PostgreSQL builtin data types.</p>
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<h3><a id="utils_cache" name="utils_cache"></a> <a
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href="../../backend/utils/cache">utils/cache</a> -
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system/relation/function cache routines</h3>
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<p>PostgreSQL supports arbitrary data types, so no data types are
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hard-coded into the core backend routines. When the backend needs
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to find out about a type, is does a lookup of a system table.
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Because these system tables are referred to often, a cache is
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maintained that speeds lookups. There is a system relation cache, a
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function/operator cache, and a relation information cache. This
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last cache maintains information about all recently-accessed
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tables, not just system ones.</p>
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<h3><a id="utils_error" name="utils_error"></a> <a
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href="../../backend/utils/error">utils/error</a> - error reporting
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routines</h3>
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<p>Reports backend errors to the front end.</p>
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<h3><a id="utils_fmgr" name="utils_fmgr"></a> <a
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href="../../backend/utils/fmgr">utils/fmgr</a> - function
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manager</h3>
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<p>This handles the calling of dynamically-loaded functions, and
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the calling of functions defined in the system tables.</p>
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<h3><a id="utils_hash" name="utils_hash"></a> <a
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href="../../backend/utils/hash">utils/hash</a> - hash routines for
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internal algorithms</h3>
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<p>These hash routines are used by the cache and memory-manager
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routines to do quick lookups of dynamic data storage structures
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maintained by the backend.</p>
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<h3><a id="utils_init" name="utils_init"></a> <a
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href="../../backend/utils/init">utils/init</a> - various
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initialization stuff</h3>
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<h3><a id="utils_mb" name="utils_mb"></a> <a
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href="../../backend/utils/mb">utils/mb</a> - single and multibyte
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encoding</h3>
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<h3><a id="utils_misc" name="utils_misc"></a> <a
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href="../../backend/utils/misc">utils/misc</a> - miscellaneous
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stuff</h3>
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<h3><a id="utils_mmgr" name="utils_mmgr"></a> <a
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href="../../backend/utils/mmgr">utils/mmgr</a> - memory
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manager(process-local memory)</h3>
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<p>When PostgreSQL allocates memory, it does so in an explicit
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context. Contexts can be statement-specific, transaction-specific,
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or persistent/global. By doing this, the backend can easily free
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memory once a statement or transaction completes.</p>
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<h3><a id="utils_resowner" name="utils_resowner"></a> <a
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href="../../backend/utils/resowner">utils/resowner</a> - resource
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owner tracking</h3>
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<h3><a id="utils_sort" name="utils_sort"></a> <a
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href="../../backend/utils/sort">utils/sort</a> - sort routines for
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internal algorithms</h3>
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<p>When statement output must be sorted as part of a backend
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operation, this code sorts the tuples, either in memory or using
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disk files.</p>
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<h3><a id="utils_time" name="utils_time"></a> <a
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href="../../backend/utils/time">utils/time</a> - transaction time
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qualification routines</h3>
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<p>These routines do checking of tuple internal columns to
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determine if the current row is still valid, or is part of a
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non-committed transaction or superseded by a new row.</p>
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<h2><a id="include" name="include"></a> <a
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href="../../backend/include">include</a> - include files</h2>
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<p>There are include directories for each subsystem.</p>
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<h2><a id="lib" name="lib"></a> <a href="../../backend/lib">lib</a>
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- support library</h2>
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<p>This houses several generic routines.</p>
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<h2><a id="regex" name="regex"></a> <a
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href="../../backend/regex">regex</a> - regular expression
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library</h2>
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<p>This is used for regular expression handling in the backend,
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i.e. '~'.</p>
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<h2><a id="port" name="port"></a> <a
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href="../../backend/port">port</a> - compatibility routines</h2>
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<br />
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<hr />
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<small>Maintainer: Bruce Momjian ( <a
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href="mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</a>
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)<br />
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Last updated: Fri May 6 14:22:27 EDT 2005</small>
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</body>
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</html>
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2 1 1 2 32 7 1 0 -1 4.000 0 0 -1 1 0 2
|
||||
0 0 2.00 150.00 180.00
|
||||
2400 7200 2400 7800
|
||||
2 1 1 2 32 7 1 0 -1 4.000 0 0 -1 1 0 2
|
||||
0 0 2.00 150.00 180.00
|
||||
2400 6000 2400 6600
|
||||
2 1 1 2 32 7 1 0 -1 4.000 0 0 -1 1 0 2
|
||||
0 0 2.00 150.00 180.00
|
||||
2400 4800 2400 5400
|
||||
2 1 1 2 32 7 1 0 -1 4.000 0 0 -1 1 0 2
|
||||
0 0 2.00 150.00 180.00
|
||||
3600 5700 5100 5700
|
||||
2 1 0 2 25 7 0 0 -1 0.000 0 0 -1 1 0 2
|
||||
0 0 2.00 150.00 180.50
|
||||
2400 900 2400 1500
|
||||
2 4 0 1 -1 8 1 0 20 0.000 0 0 7 0 0 5
|
||||
7500 6000 5100 6000 5100 5400 7500 5400 7500 6000
|
||||
2 4 0 1 33 33 3 0 20 0.000 0 0 40 0 0 5
|
||||
8700 11100 300 11100 300 3600 8700 3600 8700 11100
|
||||
2 1 0 2 29 7 0 0 -1 0.000 0 0 -1 1 1 2
|
||||
0 0 2.00 150.00 180.00
|
||||
0 0 2.00 150.00 180.00
|
||||
3150 13050 3150 13650
|
||||
2 1 0 2 29 7 0 0 -1 0.000 0 0 -1 1 1 2
|
||||
0 0 2.00 150.00 180.00
|
||||
0 0 2.00 150.00 180.00
|
||||
1500 12450 1500 11850
|
||||
2 4 0 1 -1 29 1 0 20 0.000 0 0 7 0 0 5
|
||||
2700 13050 300 13050 300 12450 2700 12450 2700 13050
|
||||
2 4 0 1 -1 29 1 0 20 0.000 0 0 7 0 0 5
|
||||
6000 13050 3600 13050 3600 12450 6000 12450 6000 13050
|
||||
2 4 0 1 -1 29 1 0 20 0.000 0 0 7 0 0 5
|
||||
7500 14250 5100 14250 5100 13650 7500 13650 7500 14250
|
||||
2 4 0 1 -1 29 1 0 20 0.000 0 0 7 0 0 5
|
||||
4200 14250 1800 14250 1800 13650 4200 13650 4200 14250
|
||||
2 1 0 2 29 7 0 0 -1 0.000 0 0 -1 1 1 2
|
||||
0 0 2.00 150.00 180.00
|
||||
0 0 2.00 150.00 180.00
|
||||
4800 12450 4800 11850
|
||||
2 1 0 2 29 7 0 0 -1 0.000 0 0 -1 1 1 2
|
||||
0 0 2.00 150.00 180.00
|
||||
0 0 2.00 150.00 180.00
|
||||
6300 13050 6300 13650
|
||||
2 4 0 1 -1 29 1 0 20 0.000 0 0 7 0 0 5
|
||||
9300 13050 6600 13050 6600 12450 9300 12450 9300 13050
|
||||
2 1 0 2 29 7 0 0 -1 0.000 0 0 -1 1 1 2
|
||||
0 0 2.00 150.00 180.00
|
||||
0 0 2.00 150.00 180.00
|
||||
7950 11850 7950 12450
|
||||
2 1 1 2 5 7 1 0 -1 4.000 0 0 -1 1 0 2
|
||||
0 0 2.00 150.00 180.00
|
||||
2400 6000 2400 6600
|
||||
2 1 1 2 32 7 1 0 -1 4.000 0 0 -1 1 0 2
|
||||
0 0 2.00 150.00 180.00
|
||||
2400 9600 2400 10200
|
||||
3 2 2 2 20 7 0 0 -1 6.000 1 1 0 5
|
||||
0 0 2.00 150.00 180.00
|
||||
2415 2140 3090 2440 5265 2515 6090 2590 6315 2740
|
||||
0.000 -1.000 -1.000 -1.000 0.000
|
||||
3 0 1 2 32 7 1 0 -1 4.500 0 1 0 7
|
||||
0 0 2.00 150.00 150.00
|
||||
7500 5700 8400 5400 8400 4500 7800 3900 3600 3900 3000 3900
|
||||
2700 4200
|
||||
0.000 1.000 1.000 1.000 1.000 1.000 0.000
|
||||
3 0 1 2 32 7 0 0 -1 4.000 0 1 0 8
|
||||
0 0 2.00 150.00 150.00
|
||||
1125 10500 900 10350 675 9975 675 4350 900 3975 1350 3900
|
||||
1800 3900 2100 4200
|
||||
0.000 1.000 1.000 1.000 1.000 1.000 1.000 0.000
|
||||
4 1 5 2 0 28 18 0.0000 4 285 870 4350 5625 utility\001
|
||||
4 1 -1 0 0 16 18 0.0000 4 210 1455 2400 1950 Postmaster\001
|
||||
4 1 -1 0 0 16 18 0.0000 4 270 1125 2400 3150 Postgres\001
|
||||
4 1 -1 0 0 16 18 0.0000 4 270 1125 6300 3150 Postgres\001
|
||||
4 1 7 0 0 16 18 0.0000 4 270 720 6300 1350 Libpq\001
|
||||
4 1 -1 0 0 16 18 0.0000 4 210 615 2400 750 Main\001
|
||||
4 1 7 0 0 16 18 0.0000 4 210 1815 2400 9450 Generate Plan\001
|
||||
4 1 7 0 0 16 18 0.0000 4 270 1440 2400 5850 Traffic Cop\001
|
||||
4 1 7 0 0 16 18 0.0000 4 210 1980 2400 8250 Generate Paths\001
|
||||
4 1 5 2 0 28 18 0.0000 4 225 615 2400 9900 Plan\001
|
||||
4 1 5 2 0 28 18 0.0000 4 285 1920 2400 8700 Optimal Path\001
|
||||
4 1 5 2 0 28 18 0.0000 4 285 900 2400 6300 Query\001
|
||||
4 1 7 0 0 16 18 0.0000 4 210 1680 2400 10650 Execute Plan\001
|
||||
4 0 5 0 0 16 12 0.0000 4 210 2640 5250 6300 e.g. CREATE TABLE, COPY\001
|
||||
4 1 5 0 0 16 12 0.0000 4 195 3540 2400 6525 SELECT, INSERT, UPDATE, DELETE\001
|
||||
4 1 7 0 0 16 18 0.0000 4 270 1800 2400 7050 Rewrite Query\001
|
||||
4 1 7 0 0 16 18 0.0000 4 210 2130 2400 4650 Parse Statement\001
|
||||
4 1 7 0 0 16 18 0.0000 4 270 720 6300 5700 Utility\001
|
||||
4 1 7 0 0 16 18 0.0000 4 210 1335 6300 6000 Command\001
|
||||
4 1 -1 0 0 16 18 0.0000 4 270 2355 7950 12900 Storage Managers\001
|
||||
4 1 -1 0 0 16 18 0.0000 4 270 1020 4800 12900 Catalog\001
|
||||
4 1 -1 0 0 16 18 0.0000 4 210 915 1500 12900 Utilities\001
|
||||
4 1 -1 0 0 16 18 0.0000 4 210 2085 3000 14100 Access Methods\001
|
||||
4 1 -1 0 0 16 18 0.0000 4 210 1635 6300 14100 Nodes / Lists\001
|
||||
Binary file not shown.
|
Before Width: | Height: | Size: 490 KiB |
|
|
@ -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>
|
||||
Loading…
Reference in New Issue