Re: We need to log aborted autovacuums

Simon Riggs wrote:
> I'm fairly confused by this thread.
>   

That's becuase you think it has something to do with cancellation, which 
it doesn't.  The original report here noted a real problem but got the 
theorized cause wrong.  It turns out the code that acquires a lock when 
autovacuum decides it is going to process something will wait forever 
for that lock to be obtained.  It cannot be the case that other locks on 
the table are causing it to cancel, or as you say it would be visible in 
the logs.  Instead the AV worker will just queue up and wait for its 
turn as long as it takes.

That does mean there's all sorts of ways that your AV workers can all 
get stuck where they are waiting for a table, and there's no way to know 
when that's happening either from the logs; you'll only see it in ps or 
pg_stat_activity.  Given that I think it's actually a mild denial of 
service attack vector, this really needs an improvement.

-- 
Greg Smith   2ndQuadrant US    greg@2ndQuadrant.com   Baltimore, MD
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