Re: [HACKERS] Proposal : For Auto-Prewarm. - Mailing list pgsql-hackers

Thanks Beena,

On Tue, Feb 7, 2017 at 4:46 PM, Beena Emerson <memissemerson@gmail.com> wrote:
> Few more comments:
>
> = Background worker messages:
>
> - Workers when launched, show messages like: "logical replication launcher
> started”, "autovacuum launcher started”. We should probably have a similar
> message to show that the pg_prewarm load and dump bgworker has started.

-- Thanks, I will add startup and shutdown message.

> - "auto pg_prewarm load: number of buffers to load x”, other messages show
> space before and after “:”, we should keep it consistent through out.
>

-- I think you are testing patch 03. The latest patch_04 have
corrected same. Can you please re-test it.

>
> = Action of -1.
> I thought we decided that interval value of -1 would mean that the auto
> prewarm worker will not be run at all. With current code, -1 is explained to
> mean it will not dump. I noticed that reloading with new option as -1 stops
> both the workers but restarting loads the data and then quits. Why does it
> allow loading with -1? Please explain this better in the documents.
>

-- '-1' means we do not want to dump at all. So we decide not to
continue with launched bgworker and it exits. As per your first
comment, if I register the startup and shutdown messages for auto
pg_prewarm I think it will look better. Will try to explain it in a
better way in documentation. The "auto pg_prewarm load" will not be
affected with dump_interval value. It will always start, load(prewarm)
and then exit.

>
> = launch_pg_prewarm_dump()

> =# SELECT launch_pg_prewarm_dump();
>  launch_pg_prewarm_dump
> ------------------------
>                   53552
> (1 row)
>
> $ ps -ef | grep 53552
> b_emers+  53555   4391  0 16:21 pts/1    00:00:00 grep --color=auto 53552

-- If dump_interval = -1 "auto pg_prewarm dump" will exit immediately.

> = Function names
> - load_now could be better named as load_file, load_dumpfile or similar.
> - dump_now -> dump_buffer or  better?

I did choose load_now and dump_now to indicate we are doing it
immediately as invoking them was based on a timer/state. Probably we
can improve that but dump_buffer, load_file may not be the right
replacement.

>
> = Corrupt file
> if the dump file is corrupted, the system crashes and the prewarm bgworkers
> are not restarted. This needs to be handled better.
>
> WARNING:  terminating connection because of crash of another server process
> 2017-02-07 16:36:58.680 IST [54252] DETAIL:  The postmaster has commanded
> this server process to roll back the current transaction and exit, because
> another server process exited abnormally and possibly corrupted shared
> memory

--- Can you please paste you autopgprewarm.save file, I edited the
file manually to some illegal entry but did not see any crash.  Only
we failed to load as block number were invalid. Please share your
tests so that I can reproduce same.

> = Documentation
>
> I feel the documentation needs to be improved greatly.
>
> - The first para in pg_prewarm should mention the autoload feature too.
>
> - The new section should be named “The pg_prewarm autoload” or something
> better. "auto pg_prewarm bgworker” does not seem appropriate.  The
> configuration parameter should also be listed out clearly like in auth-delay
> page. The new function launch_pg_prewarm_dump() should be listed under
> Functions.

-- Thanks I will try to improve the documentation. And, put more details there.


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