On 2 May 2017 at 13:12, Simon Riggs <si...@2ndquadrant.com> wrote:

> What I suggest is that with logical decoding in mind we do this
> 1. Inject a new record XLOG_SNAPSHOT_START at the start of
> LogStandbySnapshot(). We start logical decoding from there.
> 2. Record any transactions that end
> 3. Now the full XLOG_RUNNING_XACTS record arrives. We apply all xacts
> that are seen as running, minus any ended between 1 and 3
> This avoids the problems for the race but without holding locks while
> we log XLOG_RUNNING_XACTS, something that was considered painful for
> Hot Standby.

Sounds like a sensible solution to me. It avoids the need for a rather
undesirable interlock between xlog and shmem commit.

 Craig Ringer                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

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