Hi,
attached is a patch adding a function pg_current_xlog_flush_location(),
which proved quite useful when investigating the ext4 data loss bug.
It's mostly what was already sent to that thread, except for docs that
were missing in the initial version.
I'll put this into 2016-01 CF.
regards
--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 60b9a09..0d67b82 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -16755,6 +16755,9 @@ SELECT set_config('log_statement_stats', 'off', false);
<primary>pg_create_restore_point</primary>
</indexterm>
<indexterm>
+ <primary>pg_current_xlog_flush_location</primary>
+ </indexterm>
+ <indexterm>
<primary>pg_current_xlog_insert_location</primary>
</indexterm>
<indexterm>
@@ -16811,6 +16814,13 @@ SELECT set_config('log_statement_stats', 'off', false);
</row>
<row>
<entry>
+ <literal><function>pg_current_xlog_flush_location()</function></literal>
+ </entry>
+ <entry><type>pg_lsn</type></entry>
+ <entry>Get current transaction log flush location</entry>
+ </row>
+ <row>
+ <entry>
<literal><function>pg_current_xlog_insert_location()</function></literal>
</entry>
<entry><type>pg_lsn</type></entry>
@@ -16943,13 +16953,14 @@ postgres=# select pg_start_backup('label_goes_here');
<function>pg_current_xlog_location</> displays the current transaction log write
location in the same format used by the above functions. Similarly,
<function>pg_current_xlog_insert_location</> displays the current transaction log
- insertion point. The insertion point is the <quote>logical</> end
- of the transaction log
- at any instant, while the write location is the end of what has actually
- been written out from the server's internal buffers. The write location
- is the end of what can be examined from outside the server, and is usually
+ insertion point and <function>pg_current_xlog_flush_location</> displays the
+ current transaction log flush point. The insertion point is the <quote>logical</>
+ end of the transaction log at any instant, while the write location is the end of
+ what has actually been written out from the server's internal buffers and flush
+ location is the location guaranteed to be written to durable storage. The write
+ location is the end of what can be examined from outside the server, and is usually
what you want if you are interested in archiving partially-complete transaction log
- files. The insertion point is made available primarily for server
+ files. The insertion and flush points are made available primarily for server
debugging purposes. These are both read-only operations and do not
require superuser permissions.
</para>
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 71fc8ff..40a17e8 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -10632,6 +10632,19 @@ GetXLogWriteRecPtr(void)
}
/*
+ * Get latest WAL flush pointer
+ */
+XLogRecPtr
+GetXLogFlushRecPtr(void)
+{
+ SpinLockAcquire(&XLogCtl->info_lck);
+ LogwrtResult = XLogCtl->LogwrtResult;
+ SpinLockRelease(&XLogCtl->info_lck);
+
+ return LogwrtResult.Flush;
+}
+
+/*
* Returns the redo pointer of the last checkpoint or restartpoint. This is
* the oldest point in WAL that we still need, if we have to restart recovery.
*/
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 329bb8c..35c581d 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -195,7 +195,7 @@ pg_current_xlog_location(PG_FUNCTION_ARGS)
}
/*
- * Report the current WAL insert location (same format as pg_start_backup etc)
+ * Report the current WAL flush location (same format as pg_start_backup etc)
*
* This function is mostly for debugging purposes.
*/
@@ -216,6 +216,27 @@ pg_current_xlog_insert_location(PG_FUNCTION_ARGS)
}
/*
+ * Report the current WAL insert location (same format as pg_start_backup etc)
+ *
+ * This function is mostly for debugging purposes.
+ */
+Datum
+pg_current_xlog_flush_location(PG_FUNCTION_ARGS)
+{
+ XLogRecPtr current_recptr;
+
+ if (RecoveryInProgress())
+ ereport(ERROR,
+ (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+ errmsg("recovery is in progress"),
+ errhint("WAL control functions cannot be executed during recovery.")));
+
+ current_recptr = GetXLogFlushRecPtr();
+
+ PG_RETURN_LSN(current_recptr);
+}
+
+/*
* Report the last WAL receive location (same format as pg_start_backup etc)
*
* This is useful for determining how much of WAL is guaranteed to be received
diff --git a/src/include/access/xlog.h b/src/include/access/xlog.h
index 790ca66..985291d 100644
--- a/src/include/access/xlog.h
+++ b/src/include/access/xlog.h
@@ -235,6 +235,7 @@ extern void GetXLogReceiptTime(TimestampTz *rtime, bool *fromStream);
extern XLogRecPtr GetXLogReplayRecPtr(TimeLineID *replayTLI);
extern XLogRecPtr GetXLogInsertRecPtr(void);
extern XLogRecPtr GetXLogWriteRecPtr(void);
+extern XLogRecPtr GetXLogFlushRecPtr(void);
extern bool RecoveryIsPaused(void);
extern void SetRecoveryPause(bool recoveryPause);
extern TimestampTz GetLatestXTime(void);
diff --git a/src/include/access/xlog_fn.h b/src/include/access/xlog_fn.h
index 3ebe966..f4575d7 100644
--- a/src/include/access/xlog_fn.h
+++ b/src/include/access/xlog_fn.h
@@ -19,6 +19,7 @@ extern Datum pg_switch_xlog(PG_FUNCTION_ARGS);
extern Datum pg_create_restore_point(PG_FUNCTION_ARGS);
extern Datum pg_current_xlog_location(PG_FUNCTION_ARGS);
extern Datum pg_current_xlog_insert_location(PG_FUNCTION_ARGS);
+extern Datum pg_current_xlog_flush_location(PG_FUNCTION_ARGS);
extern Datum pg_last_xlog_receive_location(PG_FUNCTION_ARGS);
extern Datum pg_last_xlog_replay_location(PG_FUNCTION_ARGS);
extern Datum pg_last_xact_replay_timestamp(PG_FUNCTION_ARGS);
diff --git a/src/include/catalog/pg_proc.h b/src/include/catalog/pg_proc.h
index d8640db..ca8fcd4 100644
--- a/src/include/catalog/pg_proc.h
+++ b/src/include/catalog/pg_proc.h
@@ -3154,6 +3154,8 @@ DATA(insert OID = 2849 ( pg_current_xlog_location PGNSP PGUID 12 1 0 0 0 f f f f
DESCR("current xlog write location");
DATA(insert OID = 2852 ( pg_current_xlog_insert_location PGNSP PGUID 12 1 0 0 0 f f f f t f v s 0 0 3220 "" _null_ _null_ _null_ _null_ _null_ pg_current_xlog_insert_location _null_ _null_ _null_ ));
DESCR("current xlog insert location");
+DATA(insert OID = 3330 ( pg_current_xlog_flush_location PGNSP PGUID 12 1 0 0 0 f f f f t f v s 0 0 3220 "" _null_ _null_ _null_ _null_ _null_ pg_current_xlog_flush_location _null_ _null_ _null_ ));
+DESCR("current xlog flush location");
DATA(insert OID = 2850 ( pg_xlogfile_name_offset PGNSP PGUID 12 1 0 0 0 f f f f t f i s 1 0 2249 "3220" "{3220,25,23}" "{i,o,o}" "{wal_location,file_name,file_offset}" _null_ _null_ pg_xlogfile_name_offset _null_ _null_ _null_ ));
DESCR("xlog filename and byte offset, given an xlog location");
DATA(insert OID = 2851 ( pg_xlogfile_name PGNSP PGUID 12 1 0 0 0 f f f f t f i s 1 0 25 "3220" _null_ _null_ _null_ _null_ _null_ pg_xlogfile_name _null_ _null_ _null_ ));
--
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