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Re: DELETE with LIMIT (or my first hack)

From: Dimitri Fontaine <dimitri(at)2ndQuadrant(dot)fr>
To: Andres Freund <andres(at)anarazel(dot)de>
Cc: pgsql-hackers(at)postgresql(dot)org, Marko Tiikkaja <marko(dot)tiikkaja(at)cs(dot)helsinki(dot)fi>, Andrew Dunstan <andrew(at)dunslane(dot)net>, Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, Daniel Loureiro <daniel(at)termasa(dot)com(dot)br>, Jaime Casanova <jaime(at)2ndquadrant(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Csaba Nagy <ncslists(at)googlemail(dot)com>
Subject: Re: DELETE with LIMIT (or my first hack)
Date: 2010-11-30 21:10:55
Message-ID: m239qia55s.fsf@2ndQuadrant.fr (view raw or flat)
Thread:
Lists: pgsql-hackers
Andres Freund <andres(at)anarazel(dot)de> writes:
> On Tuesday 30 November 2010 20:24:52 Marko Tiikkaja wrote:
>> I don't buy the argument either; why would you put a LIMIT there and
>> delete one row by accident when you could put a BEGIN; in front and not
>> do any damage at all?
> Because the delete of the whole table may take awfully long?

Then you just C-c and that's your ROLLBACK. Been there, seen that (a
developer came to me sweating over maybe-lost data — his chance was that
forgetting the WHERE clause, it did take long enough for him to C-c by
reflex, the oops moment).

But more to the point, I don't see that we're this much on the policy
side of things rather than on the mechanism side. This feature has real
appealing usages (cheap work queues, anti-deadlock, huge data purges
with no production locking — you do that in little steps in a loop).

To summarize, people that are arguing against are saying they will not
themselves put time on the feature more than anything else, I think. I
don't see us refusing a good implementation on the grounds that misuse
is possible.

After all, advisory locks are session based, to name another great foot
gun. If you don't think it's big enough, think about web environments
and pgbouncer in transaction pooling mode. Loads of fun.

Regards,
-- 
Dimitri Fontaine
http://2ndQuadrant.fr     PostgreSQL : Expertise, Formation et Support

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