From: Tom Lane <tgl@sss.pgh.pa.us>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: pgsql-hackers@postgresql.org
Subject: Re: VACUUM and ANALYZE disagreeing on what reltuples means
Date: Tue, 25 Jul 2017 11:04:03 -0400
Message-ID: <7087.1500995043@sss.pgh.pa.us> (raw)
In-Reply-To: <3d250597-384e-c5f4-7533-b513e366888f@2ndquadrant.com>
References: <16db4468-edfa-830a-f921-39a50498e77e@2ndquadrant.com>
<19990.1500936945@sss.pgh.pa.us>
<3d250597-384e-c5f4-7533-b513e366888f@2ndquadrant.com>
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Tomas Vondra <tomas.vondra@2ndquadrant.com> writes:
> On 7/25/17 12:55 AM, Tom Lane wrote:
>> I think the planner basically assumes that reltuples is the live
>> tuple count, so maybe we'd better change VACUUM to get in step.
> Attached is a patch that (I think) does just that. The disagreement was
> caused by VACUUM treating recently dead tuples as live, while ANALYZE
> treats both of those as dead.
> At first I was worried that this will negatively affect plans in the
> long-running transaction, as it will get underestimates (due to
> reltuples not including rows it can see). But that's a problem we
> already have anyway, you just need to run ANALYZE in the other session.
This definitely will have some impact on plans, at least in cases where
there's a significant number of unvacuumable dead tuples. So I think
it's a bit late for v10, and I wouldn't want to back-patch at all.
Please add to the next commitfest.
regards, tom lane
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To: pgsql-hackers@postgresql.org
Cc: tgl@sss.pgh.pa.us, tomas.vondra@2ndquadrant.com
Subject: Re: VACUUM and ANALYZE disagreeing on what reltuples means
In-Reply-To: <7087.1500995043@sss.pgh.pa.us>
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