Re: Better support of exported snapshots with pg_dump

On 17/10/14 06:25, Michael Paquier wrote:
> Two votes in favor of that from two committers sounds like a deal. Here
> is an refreshed version of the patch introducing --snapshot from here,
> after fixing a couple of things and adding documentation:
> http://www.postgresql.org/message-id/CA+U5nMK9+TTCff_-4MfdxWHnASTAuHuq7u7uedD57vaY28AsQA@mail.gmail.com
>

Hi,

I have two minor things:

+    printf(_("  --snapshot                   use given synchronous 
snapshot for the dump\n"));

I think this should say --snapshot=NAME or something like that to make 
it visible that you are supposed to provide the parameter.

The other thing is, you changed logic of the parallel dump behavior a 
little - before your patch it works in a way that one connection exports 
snapshot and others do "SET TRANSACTION SNAPSHOT", after your patch, 
even the connection that exported the snapshot does the "SET TRANSACTION 
SNAPSHOT" which is unnecessary. I don't see it as too big deal but I 
don't see the need to change that behavior either.

You could do something like this instead maybe?:
if (AH->sync_snapshot_id)    SET TRANSACTION SNAPSHOT
else if (AH->numWorkers > 1 && AH->remoteVersion >= 90200 && 
!dopt->no_synchronized_snapshots)    AH->sync_snapshot_id = get_synchronized_snapshot(AH);

And remove the else if for the if (dumpsnapshot) part.

--  Petr Jelinek                  http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training &
Services