On 24.09.2012 16:33, Amit Kapila wrote:
On Tuesday, September 11, 2012 10:53 PM Heikki Linnakangas wrote:
I've been working on the often-requested feature to handle timeline
changes over streaming replication. At the moment, if you kill the
master and promote a standby server, and you have another standby
server that you'd like to keep following the new master server, you
need a WAL archive in addition to streaming replication to make it
cross the timeline change. Streaming replication will just error out.
Having a WAL archive is usually a good idea in complex replication
scenarios anyway, but it would be good to not require it.
Confirm my understanding of this feature:
This feature is for case when standby-1 who is going to be promoted to
master has archive mode 'on'.
No. This is for the case where there is no WAL archive.
archive_mode='off' on all servers.
Or to be precise, you can also have a WAL archive, but this patch
doesn't affect that in any way. This is strictly about streaming
replication.
As in that case only its timeline will change.
The timeline changes whenever you promote a standby. It's not related to
whether you have a WAL archive or not.
If above is right, then there can be other similar scenario's where it can
be used:
Scenario-1 (1 Master, 1 Stand-by)
1. Master (archive_mode=on) goes down.
2. Master again comes up
3. Stand-by tries to follow it
Now in above scenario also due to timeline mismatch it gives error, but your
patch should fix it.
If the master simply crashes or is shut down, and then restarted, the
timeline doesn't change. The standby will reconnect / poll the archive,
and sync up just fine, even without this patch.
However I am not sure about splitting for RestoreArchivedFile() and
ExecuteRecoveryCommand() into separate file.
How about splitting for all Archive related functions:
static void XLogArchiveNotify(const char *xlog);
static void XLogArchiveNotifySeg(XLogSegNo segno);
static bool XLogArchiveCheckDone(const char *xlog);
static bool XLogArchiveIsBusy(const char *xlog);
static void XLogArchiveCleanup(const char *xlog);
Hmm, sounds reasonable.
In any case, it will be better if you can split it into multiple patches:
1. Having new functionality of "Switching timeline over streaming
replication"
2. Refactoring related changes.
It can make my testing and review for new feature patch little easier.
Yep, I'll go ahead and split the patch. Thanks!
- Heikki
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