Horton

xact_start for walsender & logical decoding not updated

Tomas Vondra <tomas.vondra@2ndquadrant.com>

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From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: pgsql-hackers@postgresql.org
Date: 2019-12-09T23:44:09Z
Lists: pgsql-hackers

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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.


regards

-- 
Tomas Vondra                  http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

Commits

  1. Reimplement nullification of walsender timestamp

  2. pg_stat_activity: show NULL stmt start time for walsenders