From: Tom Lane <tgl@sss.pgh.pa.us>
To: ITAGAKI Takahiro <itagaki.takahiro@oss.ntt.co.jp>
Cc: pgsql-hackers@postgresql.org
Subject: Re: Aggressive freezing in lazy-vacuum
Date: Tue, 06 Mar 2007 23:34:57 -0500
Message-ID: <14520.1173242097@sss.pgh.pa.us> (raw)
In-Reply-To: <20070307110352.5E09.ITAGAKI.TAKAHIRO@oss.ntt.co.jp>
References: <20070306181253.64A9.ITAGAKI.TAKAHIRO@oss.ntt.co.jp>
<4399.1173193354@sss.pgh.pa.us>
<20070307110352.5E09.ITAGAKI.TAKAHIRO@oss.ntt.co.jp>
ITAGAKI Takahiro <itagaki.takahiro@oss.ntt.co.jp> writes:
> Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> I said nothing about expired tuples. The point of not freezing is to
>> preserve information about the insertion time of live tuples.
> I don't know what good it will do -- for debugging?
Exactly. As an example, I've been chasing offline a report from Merlin
Moncure about duplicate entries in a unique index; I still don't know
what exactly is going on there, but the availability of knowledge about
which transactions inserted which entries has been really helpful. If
we had a system designed to freeze tuples as soon as possible, that info
would have been gone forever pretty soon after the problem happened.
I don't say that this behavior can never be acceptable, but you need
much more than a marginal performance improvement to convince me that
it's worth the loss of forensic information.
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, itagaki.takahiro@oss.ntt.co.jp, pgsql-hackers@postgresql.org
Subject: Re: Aggressive freezing in lazy-vacuum
In-Reply-To: <14520.1173242097@sss.pgh.pa.us>
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