Re: [HACKERS] Proposal : For Auto-Prewarm.

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.

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


= 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.


= launch_pg_prewarm_dump()
With dump_interval=-1, Though function returns a pid, this worker is not running in the 04 patch. 03 version it was launching. Dumping is not done now.

=# 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


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


= 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

= 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.

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