Re: pg_autovacuum start-script

On Aug 27, 2004, at 3:37 PM, Matthew T. O'Connor wrote:

> Getting the startup and shutdown of pg_autovacuum coordinated with the 
> postmaster would address one of the big holes in contrib 
> (non-integrated) version of pg_autovacuum.

Yeah, so what I'm planning to write will probably just be a small 
Perl/shell script containing roughly the logic below. To me, it seems a 
bit shy of a general hole plugger, but maybe people will find it 
useful. I guess I'll post my final draft and let the community have at 
improving it.

>> The behavior I'm considering is:
>> if pg_ctl status returns a good value then
>>   if pg_autovacuum is not running then
>>     start pg_autovacuum
>>   else
>>     error
>> else
>>   error
>> Based on what I (think I) know, this covers the cases where:
>> 1. There is not a valid instance of postgres running.
>> 2. There is already a valid instance of pg_autovacuum running (which 
>> can still run as a daemon even in the event that postgres is stopped, 
>> IIRC).
>> 3. It is safe to start pg_autovacuum because neither of the above 
>> cases holds.
>
> pg_autovacuum will exit when it can no longer connect to a postmaster. 
> The problem is that it might sleep for several minutes before it 
> notices that the postmaster has shutdown.  So, you can restart the 
> postmaster and as long as pg_autovacuum never noticed that it went 
> away, it will keep chugging along as if nothing happened.
>
> Is there anyway pg_autovacuum can know if the postmaster has 
> restarted?  New PID? Or something better?

Hmm. If the above situation is true, does it matter whether 
pg_autovacuum knows whether the postmaster restarted?

>> Is this logic sufficiently sane?
>
> Well if the script also sends a kill signal to pg_autovacuum that 
> might solve the pg_autovacuum still running problem.

Based on what you say above, though, is it even necessary to kill it? 
Why not just observe that it's running and fail to start a new one? 
Unless there's a need to restart pg_autovacuum if postmaster restarts.

-tfo