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List:       wikitech-l
Subject:    [Wikitech-l]  Can we kill DBO_TRX? It seems evil!
From:       Asher Feldman <afeldman () wikimedia ! org>
Date:       2012-09-26 10:06:15
Message-ID: CAEhQiY9m35CP13Z7SsD64PBB_eNYsDTx6tYPYjLnUppgdh3Rdw () mail ! gmail ! com
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On Wednesday, September 26, 2012, Daniel Kinzler wrote:
>
> I see your point. But if we have the choice between lock contention and
> silent
> data loss, which is better?


This isn't really a choice - by default, when a statement in mysql hits a
lock timeout, it is rolled back but the transaction it's in is not. That
 can also lead to data loss via partial writes in real world cases if not
properly accounted for by the application.

Avoiding holding locks longer than needed really should be paramount.
Developers need to adapt  to cases where transaction semantics alone can't
guarantee consistancy across multiple write statements. We're planning on
sharding some tables this year and there will be cases where writes will
have to go to multiple database servers, likely without the benefit of two
phase commit. That doesn't mean that we should give up on consistancy or
that we shouldn't try to do better, but not in exchange for more lock
contention.
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