Re: WAL Restore process during recovery

On Tue, Jan 24, 2012 at 12:23 AM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> On Mon, Jan 23, 2012 at 12:23 PM, Fujii Masao <masao(dot)fujii(at)gmail(dot)com> wrote:
>> Why does walrestore need to be invoked even when restore_command is
>> not specified? It seems to be useless. We invoke walreceiver only when
>> primary_conninfo is specified now. Similarly we should invoke walrestore
>> only when restore_command is specified?
>
> walreceiver is shutdown and restarted in case of failed connection.
> That never happens with walrestore because the command is run each
> time - when we issue system(3) a new process is forked to run the
> command. So there is no specific cleanup to perform and so no reason
> for a managed cleanup process.
>
> So I can't see a specific reason to change that. Do you think it makes
> a difference?

Yes. When restore_command is not specified in recovery.conf, walrestore
process doesn't do any useful activity and just wastes CPU cycle. Which
might be harmless for a functionality of recovery, but ISTM it's better not
to start up walrestore in that case to avoid the waste of cycle.

> Cleaned up the points noted, new patch attached in case you wish to
> review further.
>
> Still has bug, so still with me to fix.

Thanks! Will review further.

Regards,

--
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center