Report WAL flush, not insert, position in replication IDENTIFY_SYSTEM

When beginning streaming replication, the client usually issues the
IDENTIFY_SYSTEM command, which used to return the current WAL insert
position. That's not suitable for the intended purpose of that field,
however. pg_receivexlog uses it to start replication from the reported
point, but if it hasn't been flushed to disk yet, it will fail. Change
IDENTIFY_SYSTEM to report the flush position instead.

Backpatch to 9.1 and above. 9.0 doesn't report any WAL position.

diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index 31bbc0d4c2e3c721b76eec510ea36164a6ef812a..cec56978b7489e9e2085eb111a232c0d090a0fff 100644 (file)
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -1369,7 +1369,7 @@ The commands accepted in walsender mode are:
       </term>
       <listitem>
       <para>
-       Current xlog write location. Useful to get a known location in the
+       Current xlog flush location. Useful to get a known location in the
        transaction log where streaming can start.
       </para>
       </listitem>

diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index f593c529842d8ee42f47419548a3bf82d0592c9a..121b33d2ab77dedf48f4b223c7041df1232efa6d 100644 (file)
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -315,7 +315,7 @@ IdentifySystem(void)
                logptr = GetStandbyFlushRecPtr();
        }
        else
-               logptr = GetInsertRecPtr();
+               logptr = GetFlushRecPtr();
 
        snprintf(tli, sizeof(tli), "%u", ThisTimeLineID);