On Wed, 2021-06-16 at 16:17 -0700, Andres Freund wrote:
> I think we should explicitly compute the current timeline before
> using
> ThisTimelineID. E.g. in StartReplication() call a new version of
> GetFlushRecPtr() that also returns the current timeline id.
I think all we need to do is follow the pattern in IdentifySystem() by
calling:
am_cascading_walsender = RecoveryInProgress();
first. There are three cases:
1. If the server was a primary the last time RecoveryInProgress() was
called, and it's still a primary, then it returns false immediately.
ThisTimeLineID should be set properly already.
2. If the server was a secondary the last time RecoveryInProgress() was
called, and now it's a primary, then it updates ThisTimeLineID in
InitXLOGAccess() and returns false.
3. If the server was a secondary the last time, and is still a
secondary, then it returns true. Then, StartReplication() will call
GetStandbyFlushRecPtr(), which will update ThisTimeLineID.
It was confusing to me for a while because I was trying to sort out
whether am_cascading_walsender and/or ThisTimeLineID could be out of
date, and how that would result in not updating ThisTimeLineID; and
also why there was a difference between IdentifySystem() and
StartReplication().
Simple patch attached. I didn't test it yet, but wanted to post my
analysis.
Regards,
Jeff Davis
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 32245363561..17cb21220e0 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -573,11 +573,6 @@ StartReplication(StartReplicationCmd *cmd)
StringInfoData buf;
XLogRecPtr FlushPtr;
- if (ThisTimeLineID == 0)
- ereport(ERROR,
- (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
- errmsg("IDENTIFY_SYSTEM has not been run before START_REPLICATION")));
-
/* create xlogreader for physical replication */
xlogreader =
XLogReaderAllocate(wal_segment_size, NULL,
@@ -619,6 +614,7 @@ StartReplication(StartReplicationCmd *cmd)
* that. Otherwise use the timeline of the last replayed record, which is
* kept in ThisTimeLineID.
*/
+ am_cascading_walsender = RecoveryInProgress();
if (am_cascading_walsender)
{
/* this also updates ThisTimeLineID */
