Re: ALTER TABLE lock strength reduction patch is unsafe Reply-To:

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Andres Freund <andres(at)2ndquadrant(dot)com>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Stephen Frost <sfrost(at)snowman(dot)net>, Atri Sharma <atri(dot)jiit(at)gmail(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Noah Misch <noah(at)leadboat(dot)com>, Peter Geoghegan <pg(at)heroku(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: ALTER TABLE lock strength reduction patch is unsafe Reply-To:
Date: 2014-03-04 20:08:37
Message-ID: 13336.1393963717@sss.pgh.pa.us
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Andres Freund <andres(at)2ndquadrant(dot)com> writes:
> On 2014-03-04 11:40:10 -0500, Tom Lane wrote:
>> I don't care for (2). I'd like to have lock strength reduction as
>> much as anybody, but it can't come at the price of reduction of
>> reliability.

> I am sorry, but I think this is vastly overstating the scope of the
> pg_dump problem. CREATE INDEX *already* doesn't require a AEL, and the
> amount of problems that has caused in the past is surprisingly low.

CREATE INDEX happens to be okay because pg_dump won't try to dump indexes
it doesn't see in its snapshot, ie the list of indexes to dump is created
client-side. CREATE INDEX CONCURRENTLY, otoh, already did break pg_dump,
and we had to hack things to fix it; see commit
683abc73dff549e94555d4020dae8d02f32ed78b.

regards, tom lane

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