7 files changed, 146 insertions, 5 deletions
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index ea312224bf2..6901e71f9d3 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -11189,8 +11189,8 @@ LOG:  CleanUpLock: deleting: lock(0xb7acd844) id(24688,24696,0,0,0,1)
         <literal>heap2</literal>, <literal>btree</literal>, <literal>hash</literal>,
         <literal>gin</literal>, <literal>gist</literal>, <literal>sequence</literal>,
         <literal>spgist</literal>, <literal>brin</literal>, and <literal>generic</literal>.
-        Only superusers and users with the appropriate <literal>SET</literal>
-        privilege can change this setting.
+        Extensions may define additional resource managers. Only superusers and users with
+        the appropriate <literal>SET</literal> privilege can change this setting.
        </para>
       </listitem>
      </varlistentry>
diff --git a/doc/src/sgml/custom-rmgr.sgml b/doc/src/sgml/custom-rmgr.sgml
new file mode 100644
index 00000000000..17a4f1dfbde
--- /dev/null
+++ b/doc/src/sgml/custom-rmgr.sgml
@@ -0,0 +1,98 @@
+<!-- doc/src/sgml/custom-rmgr.sgml -->
+
+<chapter id="custom-rmgr">
+ <title>Custom WAL Resource Managers</title>
+
+ <para>
+  This chapter explains the interface between the core
+  <productname>PostgreSQL</productname> system and custom WAL resource
+  managers, which enable extensions to integrate directly with the <link
+  linkend="wal"><acronym>WAL</acronym></link>.
+ </para>
+ <para>
+  An extension, especially a <link linkend="tableam">Table Access
+  Method</link> or <link linkend="indexam">Index Access Method</link>, may
+  need to use WAL for recovery, replication, and/or <link
+  linkend="logicaldecoding">Logical Decoding</link>. Custom resource managers
+  are a more flexible alternative to <link linkend="generic-wal">Generic
+  WAL</link> (which does not support logical decoding), but more complex for
+  an extension to implement.
+ </para>
+ <para>
+  To create a new custom WAL resouce manager, first define an
+  <structname>RmgrData</structname> structure with implementations for the
+  resource manager methods. Refer to
+  <filename>src/backend/access/transam/README</filename> and
+  <filename>src/include/access/xlog_internal.h</filename> in the
+  <productname>PostgreSQL</productname> source.
+<programlisting>
+/*
+ * Method table for resource managers.
+ *
+ * This struct must be kept in sync with the PG_RMGR definition in
+ * rmgr.c.
+ *
+ * rm_identify must return a name for the record based on xl_info (without
+ * reference to the rmid). For example, XLOG_BTREE_VACUUM would be named
+ * "VACUUM". rm_desc can then be called to obtain additional detail for the
+ * record, if available (e.g. the last block).
+ *
+ * rm_mask takes as input a page modified by the resource manager and masks
+ * out bits that shouldn't be flagged by wal_consistency_checking.
+ *
+ * RmgrTable[] is indexed by RmgrId values (see rmgrlist.h). If rm_name is
+ * NULL, the corresponding RmgrTable entry is considered invalid.
+ */
+typedef struct RmgrData
+{
+    const char *rm_name;
+    void        (*rm_redo) (XLogReaderState *record);
+    void        (*rm_desc) (StringInfo buf, XLogReaderState *record);
+    const char *(*rm_identify) (uint8 info);
+    void        (*rm_startup) (void);
+    void        (*rm_cleanup) (void);
+    void        (*rm_mask) (char *pagedata, BlockNumber blkno);
+    void        (*rm_decode) (struct LogicalDecodingContext *ctx,
+                              struct XLogRecordBuffer *buf);
+} RmgrData;
+</programlisting>  
+ </para>
+ <para>
+  Then, register your new resource
+  manager.
+
+<programlisting>
+/*
+ * Register a new custom WAL resource manager.
+ *
+ * Resource manager IDs must be globally unique across all extensions. Refer
+ * to https://wiki.postgresql.org/wiki/CustomWALResourceManager to reserve a
+ * unique RmgrId for your extension, to avoid conflicts with other extension
+ * developers. During development, use RM_EXPERIMENTAL_ID to avoid needlessly
+ * reserving a new ID.
+ */
+extern void RegisterCustomRmgr(RmgrId rmid, RmgrData *rmgr);
+</programlisting>
+  <function>RegisterCustomRmgr</function> must be called from the
+  extension module's <link linkend="xfunc-c-dynload">_PG_init</link> function.
+  While developing a new extension, use <literal>RM_EXPERIMENTAL_ID</literal>
+  for <parameter>rmid</parameter>. When you ready to release the extension to
+  users, reserve a new resource manager ID at the <ulink
+  url="https://wiki.postgresql.org/wiki/CustomWALResourceManagers">Custom WAL
+  Resource Manager</ulink> page.
+ </para>
+
+ <para>
+  Place the extension module implementing the custom resource manager in <xref
+  linkend="guc-shared-preload-libraries"/> so that it will be loaded early
+  during <productname>PostgreSQL</productname> startup.
+ </para>
+ <note>
+   <para>    
+    The extension must remain in shared_preload_libraries as long as any
+    custom WAL records may exist in the system. Otherwise
+    <productname>PostgreSQL</productname> will not be able to apply or decode
+    the custom WAL records, which may prevent the server from starting.
+   </para>
+ </note>
+</chapter>
diff --git a/doc/src/sgml/filelist.sgml b/doc/src/sgml/filelist.sgml
index fd853af01fa..7dea670969c 100644
--- a/doc/src/sgml/filelist.sgml
+++ b/doc/src/sgml/filelist.sgml
@@ -105,6 +105,7 @@
 <!ENTITY storage    SYSTEM "storage.sgml">
 <!ENTITY tablesample-method SYSTEM "tablesample-method.sgml">
 <!ENTITY generic-wal SYSTEM "generic-wal.sgml">
+<!ENTITY custom-rmgr SYSTEM "custom-rmgr.sgml">
 <!ENTITY backup-manifest SYSTEM "backup-manifest.sgml">
 
 <!-- contrib information -->
diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 0cf513100b6..2f7aff9f216 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -26001,6 +26001,25 @@ postgres=# SELECT * FROM pg_walfile_name_offset((pg_backup_stop()).lsn);
         without recovery, the function returns <literal>NULL</literal>.
        </para></entry>
       </row>
+
+      <row>
+       <entry role="func_table_entry"><para role="func_signature">
+        <indexterm>
+         <primary>pg_get_wal_resource_managers</primary>
+        </indexterm>
+        <function>pg_get_wal_resource_managers</function> ()
+        <returnvalue>setof record</returnvalue>
+        ( <parameter>rm_id</parameter> <type>integer</type>,
+        <parameter>rm_name</parameter> <type>text</type>,
+        <parameter>rm_builtin</parameter> <type>boolean</type> )
+       </para>
+       <para>
+        Returns the currently-loaded WAL resource managers in the system. The
+        column <parameter>rm_builtin</parameter> indicates whether it's a
+        built-in resource manager, or a custom resource manager loaded by an
+        extension.
+       </para></entry>
+      </row>
      </tbody>
     </tgroup>
    </table>
diff --git a/doc/src/sgml/generic-wal.sgml b/doc/src/sgml/generic-wal.sgml
index 7a0284994c9..a028856d2eb 100644
--- a/doc/src/sgml/generic-wal.sgml
+++ b/doc/src/sgml/generic-wal.sgml
@@ -6,12 +6,26 @@
   <para>
    Although all built-in WAL-logged modules have their own types of WAL
    records, there is also a generic WAL record type, which describes changes
-   to pages in a generic way.  This is useful for extensions that provide
-   custom access methods, because they cannot register their own WAL redo
-   routines.
+   to pages in a generic way. This is useful for extensions that provide
+   custom access methods.
   </para>
 
   <para>
+   In comparison with <link linkend="custom-rmgr">Custom WAL Resource
+   Managers</link>, Generic WAL is simpler for an extension to implement and
+   does not require the extension library to be loaded in order to apply the
+   records.
+  </para>
+
+  <note>
+   <para>
+    Generic WAL records are ignored during <link
+    linkend="logicaldecoding">Logical Decoding</link>. If logical decoding is
+    required for your extension, consider a Custom WAL Resource Manager.
+   </para>
+  </note>
+
+  <para>
    The API for constructing generic WAL records is defined in
    <filename>access/generic_xlog.h</filename> and implemented
    in <filename>access/transam/generic_xlog.c</filename>.
diff --git a/doc/src/sgml/postgres.sgml b/doc/src/sgml/postgres.sgml
index 3db6d2160b1..0b60e46d69d 100644
--- a/doc/src/sgml/postgres.sgml
+++ b/doc/src/sgml/postgres.sgml
@@ -262,6 +262,7 @@ break is not needed in a wider output rendering.
   &tableam;
   &indexam;
   &generic-wal;
+  &custom-rmgr;
   &btree;
   &gist;
   &spgist;
diff --git a/doc/src/sgml/ref/pg_waldump.sgml b/doc/src/sgml/ref/pg_waldump.sgml
index 1a05af5d972..57746d9421f 100644
--- a/doc/src/sgml/ref/pg_waldump.sgml
+++ b/doc/src/sgml/ref/pg_waldump.sgml
@@ -173,6 +173,14 @@ PostgreSQL documentation
         If <literal>list</literal> is passed as name, print a list of valid resource manager
         names, and exit.
        </para>
+       <para>
+        Extensions may define custom resource managers, but pg_waldump does
+        not load the extension module and therefore does not recognize custom
+        resource managers by name. Instead, you can specify the custom
+        resource managers as <literal>custom###</literal> where
+        "<literal>###</literal>" is the three-digit resource manager ID. Names
+        of this form will always be considered valid.
+       </para>
       </listitem>
      </varlistentry>