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 08c2f008936b76e4f0f339028ae85d0c3ebc358b..87741f3b374b98447acf4a190947d151e8632210 100644 (file)
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -1338,7 +1338,7 @@ 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 7deaa82fd64ea96e551b0ad587b4d56e6c93b3d0..94da622f057ccbc9771997b3c1bf4d1dd73f86ca 100644 (file)
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -298,7 +298,7 @@ IdentifySystem(void)
                         GetSystemIdentifier());
        snprintf(tli, sizeof(tli), "%u", ThisTimeLineID);
 
-       logptr = am_cascading_walsender ? GetStandbyFlushRecPtr(NULL) : GetInsertRecPtr();
+       logptr = am_cascading_walsender ? GetStandbyFlushRecPtr(NULL) : GetFlushRecPtr();
 
        snprintf(xpos, sizeof(xpos), "%X/%X",
                         logptr.xlogid, logptr.xrecoff);