From 325f2ec5557fd1c9156c910102522e04cb42d99c Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter_e@gmx.net>
Date: Wed, 21 Mar 2018 09:13:24 -0400
Subject: Handle heap rewrites even better in logical decoding

Logical decoding should not publish anything about tables created as
part of a heap rewrite during DDL.  Those tables don't exist externally,
so consumers of logical decoding cannot do anything sensible with that
information.  In ab28feae2bd3d4629bd73ae3548e671c57d785f0, we worked
around this for built-in logical replication, but that was hack.

This is a more proper fix: We mark such transient heaps using the new
field pg_class.relwrite, linking to the original relation OID.  By
default, we ignore them in logical decoding before they get to the
output plugin.  Optionally, a plugin can register their interest in
getting such changes, if they handle DDL specially, in which case the
new field will help them get information about the actual table.

Reviewed-by: Craig Ringer <craig@2ndquadrant.com>
---
 doc/src/sgml/catalogs.sgml        | 12 ++++++++++++
 doc/src/sgml/logicaldecoding.sgml |  5 +++++
 2 files changed, 17 insertions(+)

(limited to 'doc/src')

diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml
index 30e67413050..fc81133f07d 100644
--- a/doc/src/sgml/catalogs.sgml
+++ b/doc/src/sgml/catalogs.sgml
@@ -1923,6 +1923,18 @@ SCRAM-SHA-256$<replaceable>&lt;iteration count&gt;</replaceable>:<replaceable>&l
       <entry>True if table is a partition</entry>
      </row>
 
+     <row>
+      <entry><structfield>relrewrite</structfield></entry>
+      <entry><type>oid</type></entry>
+      <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
+      <entry>
+       For new relations being written during a DDL operation that requires a
+       table rewrite, this contains the OID of the original relation;
+       otherwise 0.  That state is only visible internally; this field should
+       never contain anything other than 0 for a user-visible relation.
+      </entry>
+     </row>
+
      <row>
       <entry><structfield>relfrozenxid</structfield></entry>
       <entry><type>xid</type></entry>
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 5501eed1086..f6b14dccb09 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -486,12 +486,17 @@ typedef void (*LogicalDecodeStartupCB) (struct LogicalDecodingContext *ctx,
 typedef struct OutputPluginOptions
 {
     OutputPluginOutputType output_type;
+    bool        receive_rewrites;
 } OutputPluginOptions;
 </programlisting>
       <literal>output_type</literal> has to either be set to
       <literal>OUTPUT_PLUGIN_TEXTUAL_OUTPUT</literal>
       or <literal>OUTPUT_PLUGIN_BINARY_OUTPUT</literal>. See also
       <xref linkend="logicaldecoding-output-mode"/>.
+      If <literal>receive_rewrites</literal> is true, the output plugin will
+      also be called for changes made by heap rewrites during certain DDL
+      operations.  These are of interest to plugins that handle DDL
+      replication, but they require special handling.
      </para>
 
      <para>
-- 
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