<!-- doc/src/sgml/custom-rmgr.sgml -->

<sect1 id="custom-rmgr">
 <title>Custom WAL Resource Managers</title>

 <para>
  This section 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>.
 </para>
 <para>
  To create a new custom WAL resource 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