Re: Race condition in recovery?

On Tue, Jun 8, 2021 at 12:32 AM Robert Haas <robertmhaas@gmail.com> wrote:
>
> I tried back-porting my version of this patch to 9.6 to see what would
> happen there. One problem is that some of the functions have different
> names before v10. So 9.6 needs this:
>
> -    "SELECT pg_walfile_name(pg_current_wal_lsn());");
> +    "SELECT pg_xlogfile_name(pg_current_xlog_location());");
>
> But there's also another problem, which is that this doesn't work before v12:
>
> $node_standby->psql('postgres', 'SELECT pg_promote()');
>
> So I tried changing it to this:
>
> $node_standby->promote;
>
> But then the test fails, because pg_promote() has logic built into it
> to wait until the promotion actually happens, but ->promote doesn't,
> so SELECT pg_walfile_name(pg_current_wal_lsn()) errors out because the
> system is still in recovery. I'm not sure what to do about that. I
> quickly tried adding -w to 'sub promote' in PostgresNode.pm, but that
> didn't fix it, so I guess we'll have to find some other way to wait
> until the promotion is complete.
>

Maybe we can use it ?

# Wait until the node exits recovery.
$standby->poll_query_until('postgres', "SELECT pg_is_in_recovery() = 'f';")
or die "Timed out while waiting for promotion";

I will try to generate a version for 9.6 based on this idea and see how it goes

-- 
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com