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Re: stats for failed transactions (was Re: [GENERAL] VACUUM Question)

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>
Cc: "Matthew T(dot) O'Connor" <matthew(at)zeut(dot)net>, Michael Fuhr <mike(at)fuhr(dot)org>, Jan Wieck <JanWieck(at)Yahoo(dot)com>, pgsql-hackers(at)postgreSQL(dot)org
Subject: Re: stats for failed transactions (was Re: [GENERAL] VACUUM Question)
Date: 2006-01-27 15:56:12
Message-ID: 2644.1138377372@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-generalpgsql-hackers
Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> writes:
> Tom Lane wrote:
>> I think this is unquestionably
>> a bug, at least for autovacuum's purposes --- though it might be OK
>> for the original intent of the stats system, which was simply to track
>> activity levels.
>> 
>> Any thoughts about how it ought to work?

> I don't remember exactly how it works -- I think the activity (insert,
> update, delete) counters are kept separately from commit/rollback
> status, right?  Maybe we should keep three separate counters: "current
> transaction counters" and "counters for transactions that were
> aborted/committed".  We only send the latter counts, and the former are
> added to them when the transaction ends.

My question was at a higher level, actually: *what* should we be
counting?

I think doubling the number of counters in the stats system, which is
what you seem to be proposing, is probably not acceptable --- we've
already got a problem with the stats file becoming unreasonably bulky.
We need to figure out exactly which counts there is adequate reason
to be tracking.

I don't, for instance, see any percentage in tracking block-level I/O
operations separately for committed and rolled-back transactions.
Those numbers are certainly things you watch only for total activity,
and a failed xact is just as much system load as a committed one.

			regards, tom lane

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