On 17.12.2010 19:08, Robert Haas wrote:
On Fri, Dec 17, 2010 at 11:43 AM, Tom Lane<t...@sss.pgh.pa.us> wrote:
Alvaro Herrera<alvhe...@commandprompt.com> writes:
Excerpts from Tom Lane's message of vie dic 17 13:18:35 -0300 2010:
I think what we ought to be looking to do is get rid of the distinction,
so that the postmaster treats walsenders the same as other children.
I think the problem with this is that walsenders are treated in a very
special way during shutdown -- they need to stay up until after bgwriter
is gone.
Why do they need to survive the bgwriter?
Because we want the shutdown checkpoint record that bgwriter writes just
before it dies to be replicated to the standbys.
And more to the point, why
does that logic need to be implemented on the postmaster side? Since
only the child process really knows reliably whether it's a walsender,
it'd be far safer if the behavioral difference could be handled on the
child side. I haven't looked at the details, but I'm wondering if we
couldn't make this go by having walsender children react differently
to the same signals the postmaster sends other children.
I'm not too sure we're shutting down the WAL senders right now.
Sure we do. postmaster sends walsenders SIGUSR2 when bgwriter dies. When
a walsender receives SIGUSR2, it tries to send all pending WAL, and
terminates after that. The postmaster goes into PM_SHUTDOWN_2 state,
waiting for all the walsenders and the archiver process to die.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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