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Re: autovacuum next steps, take 2

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Matthew T(dot) O'Connor" <matthew(at)zeut(dot)net>
Cc: "Jim C(dot) Nasby" <jim(at)nasby(dot)net>, Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Hackers <pgsql-hackers(at)postgresql(dot)org>, Gregory Stark <stark(at)enterprisedb(dot)com>
Subject: Re: autovacuum next steps, take 2
Date: 2007-02-27 06:20:30
Message-ID: 12844.1172557230@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
"Matthew T. O'Connor" <matthew(at)zeut(dot)net> writes:
> I'm not sure what you are saying here, are you now saying that partial 
> vacuum won't work for autovac?  Or are you saying that saving state as 
> Jim is describing above won't work?

I'm saying that I don't like the idea of trying to "stop on a dime" by
saving the current contents of vacuum's dead-TID array to disk with the
idea that we can trust those values 100% later.  Saving the array is
expensive both in runtime and code complexity, and I don't believe we
can trust it later --- at least not without even more expensive-and-
complex measures, such as WAL-logging every such save :-(

I'm for stopping only after completing an index-cleaning pass, at the
point where we empty the dead-TID array anyway.  If you really have to
have "stop on a dime", just kill -INT the process, accepting that you
will have to redo your heap scan since the last restart point.

			regards, tom lane

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