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Date: Wed, 21 Aug 2013 23:43:07 +0200
From: Vik Fearing <vik.fearing@dalibo.com>
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To: PG Hackers <pgsql-hackers@postgresql.org>
Subject: pg_system_identifier()
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After someone in IRC asked if there was an equivalent to MySQL's
server_id, it was noted that we do have a system identifier but it's not
very accessible.

The attached patch implements a pg_system_identifier() function that
exposes it.

Shall I add this to the next commitfest?

-- 
Vik


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*** a/doc/src/sgml/func.sgml
--- b/doc/src/sgml/func.sgml
***************
*** 13473,13478 **** SELECT * FROM pg_ls_dir('.') WITH ORDINALITY AS t(ls,n);
--- 13473,13484 ----
        </row>
  
        <row>
+        <entry><literal><function>pg_system_identifier()</function></literal></entry>
+        <entry><type>text</type></entry>
+        <entry>system identifier for the database cluster</entry>
+       </row>
+ 
+       <row>
         <entry><literal><function>pg_trigger_depth()</function></literal></entry>
         <entry><type>int</type></entry>
         <entry>current nesting level of <productname>PostgreSQL</> triggers
*** a/src/backend/access/transam/xlogfuncs.c
--- b/src/backend/access/transam/xlogfuncs.c
***************
*** 35,40 ****
--- 35,50 ----
  
  static void validate_xlog_location(char *str);
  
+ /*
+  * pg_system_identifier
+  */
+ Datum
+ pg_system_identifier(PG_FUNCTION_ARGS)
+ {
+ 		char	ret[32];
+ 		sprintf(ret, UINT64_FORMAT, GetSystemIdentifier());
+ 		PG_RETURN_TEXT_P(cstring_to_text(ret));
+ }
  
  /*
   * pg_start_backup: set up for taking an on-line backup dump
*** a/src/include/access/xlog_fn.h
--- b/src/include/access/xlog_fn.h
***************
*** 13,18 ****
--- 13,19 ----
  
  #include "fmgr.h"
  
+ extern Datum pg_system_identifier(PG_FUNCTION_ARGS);
  extern Datum pg_start_backup(PG_FUNCTION_ARGS);
  extern Datum pg_stop_backup(PG_FUNCTION_ARGS);
  extern Datum pg_switch_xlog(PG_FUNCTION_ARGS);
*** a/src/include/catalog/catversion.h
--- b/src/include/catalog/catversion.h
***************
*** 53,58 ****
--- 53,59 ----
   */
  
  /*							yyyymmddN */
+ /* needs bump */
  #define CATALOG_VERSION_NO	201307221
  
  #endif
*** a/src/include/catalog/pg_proc.h
--- b/src/include/catalog/pg_proc.h
***************
*** 2954,2959 **** DATA(insert OID = 2171 ( pg_cancel_backend		PGNSP PGUID 12 1 0 0 0 f f f f t f v
--- 2954,2961 ----
  DESCR("cancel a server process' current query");
  DATA(insert OID = 2096 ( pg_terminate_backend		PGNSP PGUID 12 1 0 0 0 f f f f t f v 1 0 16 "23" _null_ _null_ _null_ _null_ pg_terminate_backend _null_ _null_ _null_ ));
  DESCR("terminate a server process");
+ DATA(insert OID = 3179 ( pg_system_identifier	PGNSP PGUID 12 1 0 0 0 f f f f f f i 0 0 25 "" _null_ _null_ _null_ _null_ pg_system_identifier _null_ _null_ _null_ ));
+ DESCR("database system identifier");
  DATA(insert OID = 2172 ( pg_start_backup		PGNSP PGUID 12 1 0 0 0 f f f f t f v 2 0 25 "25 16" _null_ _null_ _null_ _null_ pg_start_backup _null_ _null_ _null_ ));
  DESCR("prepare for taking an online backup");
  DATA(insert OID = 2173 ( pg_stop_backup			PGNSP PGUID 12 1 0 0 0 f f f f t f v 0 0 25 "" _null_ _null_ _null_ _null_ pg_stop_backup _null_ _null_ _null_ ));

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