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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-05-04 12:19:15 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-05-04 12:19:15 +0000
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Adding upstream version 13.4.upstream/13.4upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
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+<!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 http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>58.1. Creating Custom Scan Paths</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets V1.79.1" /><link rel="prev" href="custom-scan.html" title="Chapter 58. Writing a Custom Scan Provider" /><link rel="next" href="custom-scan-plan.html" title="58.2. Creating Custom Scan Plans" /></head><body id="docContent" class="container-fluid col-10"><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">58.1. Creating Custom Scan Paths</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="custom-scan.html" title="Chapter 58. Writing a Custom Scan Provider">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="custom-scan.html" title="Chapter 58. Writing a Custom Scan Provider">Up</a></td><th width="60%" align="center">Chapter 58. Writing a Custom Scan Provider</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 13.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="custom-scan-plan.html" title="58.2. Creating Custom Scan Plans">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="CUSTOM-SCAN-PATH"><div class="titlepage"><div><div><h2 class="title" style="clear: both">58.1. Creating Custom Scan Paths</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="custom-scan-path.html#CUSTOM-SCAN-PATH-CALLBACKS">58.1.1. Custom Scan Path Callbacks</a></span></dt></dl></div><p>
+ A custom scan provider will typically add paths for a base relation by
+ setting the following hook, which is called after the core code has
+ generated all the access paths it can for the relation (except for
+ Gather paths, which are made after this call so that they can use
+ partial paths added by the hook):
+</p><pre class="programlisting">
+typedef void (*set_rel_pathlist_hook_type) (PlannerInfo *root,
+ RelOptInfo *rel,
+ Index rti,
+ RangeTblEntry *rte);
+extern PGDLLIMPORT set_rel_pathlist_hook_type set_rel_pathlist_hook;
+</pre><p>
+ </p><p>
+ Although this hook function can be used to examine, modify, or remove
+ paths generated by the core system, a custom scan provider will typically
+ confine itself to generating <code class="structname">CustomPath</code> objects and adding
+ them to <code class="literal">rel</code> using <code class="function">add_path</code>. The custom scan
+ provider is responsible for initializing the <code class="structname">CustomPath</code>
+ object, which is declared like this:
+</p><pre class="programlisting">
+typedef struct CustomPath
+{
+ Path path;
+ uint32 flags;
+ List *custom_paths;
+ List *custom_private;
+ const CustomPathMethods *methods;
+} CustomPath;
+</pre><p>
+ </p><p>
+ <code class="structfield">path</code> must be initialized as for any other path, including
+ the row-count estimate, start and total cost, and sort ordering provided
+ by this path. <code class="structfield">flags</code> is a bit mask, which should include
+ <code class="literal">CUSTOMPATH_SUPPORT_BACKWARD_SCAN</code> if the custom path can support
+ a backward scan and <code class="literal">CUSTOMPATH_SUPPORT_MARK_RESTORE</code> if it
+ can support mark and restore. Both capabilities are optional.
+ An optional <code class="structfield">custom_paths</code> is a list of <code class="structname">Path</code>
+ nodes used by this custom-path node; these will be transformed into
+ <code class="structname">Plan</code> nodes by planner.
+ <code class="structfield">custom_private</code> can be used to store the custom path's
+ private data. Private data should be stored in a form that can be handled
+ by <code class="literal">nodeToString</code>, so that debugging routines that attempt to
+ print the custom path will work as designed. <code class="structfield">methods</code> must
+ point to a (usually statically allocated) object implementing the required
+ custom path methods, of which there is currently only one.
+ </p><p>
+ A custom scan provider can also provide join paths. Just as for base
+ relations, such a path must produce the same output as would normally be
+ produced by the join it replaces. To do this, the join provider should
+ set the following hook, and then within the hook function,
+ create <code class="structname">CustomPath</code> path(s) for the join relation.
+</p><pre class="programlisting">
+typedef void (*set_join_pathlist_hook_type) (PlannerInfo *root,
+ RelOptInfo *joinrel,
+ RelOptInfo *outerrel,
+ RelOptInfo *innerrel,
+ JoinType jointype,
+ JoinPathExtraData *extra);
+extern PGDLLIMPORT set_join_pathlist_hook_type set_join_pathlist_hook;
+</pre><p>
+
+ This hook will be invoked repeatedly for the same join relation, with
+ different combinations of inner and outer relations; it is the
+ responsibility of the hook to minimize duplicated work.
+ </p><div class="sect2" id="CUSTOM-SCAN-PATH-CALLBACKS"><div class="titlepage"><div><div><h3 class="title">58.1.1. Custom Scan Path Callbacks</h3></div></div></div><p>
+</p><pre class="programlisting">
+Plan *(*PlanCustomPath) (PlannerInfo *root,
+ RelOptInfo *rel,
+ CustomPath *best_path,
+ List *tlist,
+ List *clauses,
+ List *custom_plans);
+</pre><p>
+ Convert a custom path to a finished plan. The return value will generally
+ be a <code class="literal">CustomScan</code> object, which the callback must allocate and
+ initialize. See <a class="xref" href="custom-scan-plan.html" title="58.2. Creating Custom Scan Plans">Section 58.2</a> for more details.
+ </p></div></div><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navfooter"><hr></hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="custom-scan.html" title="Chapter 58. Writing a Custom Scan Provider">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="custom-scan.html" title="Chapter 58. Writing a Custom Scan Provider">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="custom-scan-plan.html" title="58.2. Creating Custom Scan Plans">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 58. Writing a Custom Scan Provider </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 13.4 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 58.2. Creating Custom Scan Plans</td></tr></table></div></body></html> \ No newline at end of file
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