Re: Proposal : For Auto-Prewarm.

On Tue, Feb 7, 2017 at 12:24 PM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> On Tue, Feb 7, 2017 at 11:53 AM, Beena Emerson <memissemerson(at)gmail(dot)com> wrote:
>> Are 2 workers required?
>>
>
> I think in the new design there is a provision of launching the worker
> dynamically to dump the buffers, so there seems to be a need of
> separate workers for loading and dumping the buffers. However, there
> is no explanation in the patch or otherwise when and why this needs a
> pair of workers. Also, if the dump interval is greater than zero,
> then do we really need to separately register a dynamic worker?

We have introduced a new value -1 for pg_prewarm.dump_interval this
means we will not dump at all, At this state, I thought auto
pg_prewarm process need not run at all, so I coded to exit the auto
pg_prewarm immediately. But If the user decides to start the auto
pg_prewarm to dump only without restarting the server, I have
introduced a launcher function "launch_pg_prewarm_dump" to restart the
auto pg_prewarm only to dump. Since now we can launch worker only to
dump, I thought we can redistribute the code between two workers, one
which only does prewarm (load only) and another dumps periodically.
This helped me to modularize and reuse the code. So once load worker
has finished its job, it registers a dump worker and then exists.
But if max_worker_processes is not enough to launch the "auto
pg_prewarm dump" bgworker
We throw an error
2017-02-07 14:51:59.789 IST [50481] ERROR: registering dynamic
bgworker "auto pg_prewarm dump" failed c
2017-02-07 14:51:59.789 IST [50481] HINT: Consider increasing
configuration parameter "max_worker_processes".

Now thinking again instead of such error and then correcting same by
explicitly launching the auto pg_prewarm dump bgwroker through
launch_pg_prewarm_dump(), I can go back to original design where there
will be one worker which loads and then dumps periodically. And
launch_pg_prewarm_dump will relaunch dump only activity of that
worker. Does this sound good?

--
Thanks and Regards
Mithun C Y
EnterpriseDB: http://www.enterprisedb.com