Re: Inconsistent bgworker behaviour

From: Beena Emerson <memissemerson(at)gmail(dot)com>
To: Craig Ringer <craig(at)2ndquadrant(dot)com>
Cc: pgsql-general(at)postgresql(dot)org
Subject: Re: Inconsistent bgworker behaviour
Date: 2015-01-08 16:53:30
Message-ID: CAOG9ApGgfDRBpxPg90SBzTYDLvQh7wfDgebhN2ht-2gNVnuqRA@mail.gmail.com
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Hello,

Thank you for your reply.

> We could probably use a WaitForBackgroundWorkerTermination(...) to
> correspond to WaitForBackgroundWorkerStartup(...) .
>
> I think you'll probably want to GetBackgroundWorkerPid(...) and examine
> the returned BgwHandleStatus to see if it's BGWH_STOPPED . If not, keep
> waiting. You might want a timeout to re-check.

I have tried checking the status but I found that BGWH_STOPPED does not
imply that the background worker has unregistered.

I updated the code as suggested to check the Handle status in a loop and
added appropriate LOG messages to understand the flow.

This is the log output. The old M.datatbases value was "db1, db4".

LOG: received SIGHUP, reloading configuration files
LOG: parameter "m.databases" changed to "db1, db2"
LOG: WaitLatch Ends
LOG: The bgworker status is BGWH_STOPPED
WARNING: could not register background process for database "db2"
HINT: You may need to increase configuration parameter
"max_worker_processes".
LOG: worker process: m db4 (PID 8629) exited with exit code 0
LOG: unregistering background worker "m db4"
server signaled

As seen even though the status is BGWH_STOPPED, the slot is not free and
hence the new worker cannot be launched.

Is there any way to check if the bgworker has unregistered and freed a slot?

Thanks,

Beena

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