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Re: Synchronous Commit, WAL archiving and statement_timeout

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On 02/02/2017 09:15 AM, JP Jacoupy wrote:

Hello,

I noticed something strange and I would like to understand what's
happening.

I have the following environment:
  - 2 PostgreSQL instance running in hot-standby with synchronous commit
activated.

There have been many changes in replication over the years/versions, so it would be helpful to know what Postgres version you are using?

    (further called Master & Slave)
  - The archiving of the WAL files is activated on the master running
every 5 minutes
  - Slave is down

I set the statement_timeout inside my ~/.psqlrc:
$ cat ~/.psqlrc
set statement_timeout = 1;
commit;

When running an UPDATE statement (via psql) on the master, it hangs
(psql seems to
wait a response from the slave) ignoring any value I set in my .psqlrc
and the update is
done and written on the Master. Furthermore if I try (doing the same
things in a small
script with a timeout on the call to PQexec) to make a call to PQcancel
it does nothing
on the Master.

I expected the statement to timeout because the synchronous_commit
wouldn't work

https://www.postgresql.org/docs/9.4/static/warm-standby.html#SYNCHRONOUS-REPLICATION

"25.2.8.3. Planning for High Availability

Commits made when synchronous_commit is set to on or remote_write will wait until the synchronous standby responds. The response may never occur if the last, or only, standby should crash."

since the Slave is down while rollbacking on the Master.


--
Adrian Klaver
adrian.klaver@xxxxxxxxxxx


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