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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>Chapter 57. Writing A Foreign Data Wrapper</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 Vsnapshot" /><link rel="prev" href="plhandler.html" title="Chapter 56. Writing A Procedural Language Handler" /><link rel="next" href="fdw-functions.html" title="57.1. Foreign Data Wrapper Functions" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">Chapter 57. Writing A Foreign Data Wrapper</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="plhandler.html" title="Chapter 56. Writing A Procedural Language Handler">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="internals.html" title="Part VII. Internals">Up</a></td><th width="60%" align="center">Part VII. Internals</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 11.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="fdw-functions.html" title="57.1. Foreign Data Wrapper Functions">Next</a></td></tr></table><hr></hr></div><div class="chapter" id="FDWHANDLER"><div class="titlepage"><div><div><h2 class="title">Chapter 57. Writing A Foreign Data Wrapper</h2></div></div></div><div class="toc"><p><strong>Table of Contents</strong></p><dl class="toc"><dt><span class="sect1"><a href="fdw-functions.html">57.1. Foreign Data Wrapper Functions</a></span></dt><dt><span class="sect1"><a href="fdw-callbacks.html">57.2. Foreign Data Wrapper Callback Routines</a></span></dt><dd><dl><dt><span class="sect2"><a href="fdw-callbacks.html#FDW-CALLBACKS-SCAN">57.2.1. FDW Routines For Scanning Foreign Tables</a></span></dt><dt><span class="sect2"><a href="fdw-callbacks.html#FDW-CALLBACKS-JOIN-SCAN">57.2.2. FDW Routines For Scanning Foreign Joins</a></span></dt><dt><span class="sect2"><a href="fdw-callbacks.html#FDW-CALLBACKS-UPPER-PLANNING">57.2.3. FDW Routines For Planning Post-Scan/Join Processing</a></span></dt><dt><span class="sect2"><a href="fdw-callbacks.html#FDW-CALLBACKS-UPDATE">57.2.4. FDW Routines For Updating Foreign Tables</a></span></dt><dt><span class="sect2"><a href="fdw-callbacks.html#FDW-CALLBACKS-ROW-LOCKING">57.2.5. FDW Routines For Row Locking</a></span></dt><dt><span class="sect2"><a href="fdw-callbacks.html#FDW-CALLBACKS-EXPLAIN">57.2.6. FDW Routines for <code class="command">EXPLAIN</code></a></span></dt><dt><span class="sect2"><a href="fdw-callbacks.html#FDW-CALLBACKS-ANALYZE">57.2.7. FDW Routines for <code class="command">ANALYZE</code></a></span></dt><dt><span class="sect2"><a href="fdw-callbacks.html#FDW-CALLBACKS-IMPORT">57.2.8. FDW Routines For <code class="command">IMPORT FOREIGN SCHEMA</code></a></span></dt><dt><span class="sect2"><a href="fdw-callbacks.html#FDW-CALLBACKS-PARALLEL">57.2.9. FDW Routines for Parallel Execution</a></span></dt><dt><span class="sect2"><a href="fdw-callbacks.html#FDW-CALLBACKS-REPARAMETERIZE-PATHS">57.2.10. FDW Routines For reparameterization of paths</a></span></dt></dl></dd><dt><span class="sect1"><a href="fdw-helpers.html">57.3. Foreign Data Wrapper Helper Functions</a></span></dt><dt><span class="sect1"><a href="fdw-planning.html">57.4. Foreign Data Wrapper Query Planning</a></span></dt><dt><span class="sect1"><a href="fdw-row-locking.html">57.5. Row Locking in Foreign Data Wrappers</a></span></dt></dl></div><a id="id-1.10.9.2" class="indexterm"></a><p>
All operations on a foreign table are handled through its foreign data
wrapper, which consists of a set of functions that the core server
calls. The foreign data wrapper is responsible for fetching
data from the remote data source and returning it to the
<span class="productname">PostgreSQL</span> executor. If updating foreign
tables is to be supported, the wrapper must handle that, too.
This chapter outlines how to write a new foreign data wrapper.
</p><p>
The foreign data wrappers included in the standard distribution are good
references when trying to write your own. Look into the
<code class="filename">contrib</code> subdirectory of the source tree.
The <a class="xref" href="sql-createforeigndatawrapper.html" title="CREATE FOREIGN DATA WRAPPER"><span class="refentrytitle">CREATE FOREIGN DATA WRAPPER</span></a> reference page also has
some useful details.
</p><div class="note"><h3 class="title">Note</h3><p>
The SQL standard specifies an interface for writing foreign data wrappers.
However, PostgreSQL does not implement that API, because the effort to
accommodate it into PostgreSQL would be large, and the standard API hasn't
gained wide adoption anyway.
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