From: | Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com> |
---|---|
To: | tomas(dot)vondra(at)2ndquadrant(dot)com |
Cc: | pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: xact_start for walsender & logical decoding not updated |
Date: | 2019-12-10 00:42:17 |
Message-ID: | 20191210.094217.2248726849034272968.horikyota.ntt@gmail.com |
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Lists: | pgsql-hackers |
At Tue, 10 Dec 2019 00:44:09 +0100, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> wrote in
> Hi,
>
> I think there's a minor bug in pg_stat_activity tracking of walsender
> processes. The issue is that xact_start is only updated at the very
> beginning when the walsender starts (so it's almost exactly equal to
> backend_start) and then just flips between NULL and that value.
>
> Reproducing this is trivial - just create a publication/subscription
> with the built-in logical replication, and run arbitrary workload.
> You'll see that the xact_start value never changes.
>
> I think the right fix is calling SetCurrentStatementStartTimestamp()
> right before StartTransactionCommand() in ReorderBufferCommit, per the
> attached patch.
I'm not sure how much xact_start for walsender is useful and we really
is not running a statement there. Also autovac launcher starts
transaction without a valid statement timestamp perhaps for the same
reason.
However, if we want to show something meaningful there, I think
commit_time might be more informative there. If we use
GetCurrentTimestamp(), StartTransaction() already has the same feature
for autonomous transactions. I suppose we should do them a unified
way.
regards.
--
Kyotaro Horiguchi
NTT Open Source Software Center
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