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Re: Compressing the AFTER TRIGGER queue

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Dean Rasheed <dean(dot)a(dot)rasheed(at)gmail(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Compressing the AFTER TRIGGER queue
Date: 2011-08-01 17:46:53
Message-ID: CA+Tgmob1jWU=Zq-EQnBoPkzC+y_xW5v8O8D_Y3Y4a3d5gAPVEA@mail.gmail.com (view raw or flat)
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On Mon, Aug 1, 2011 at 1:42 PM, Dean Rasheed <dean(dot)a(dot)rasheed(at)gmail(dot)com> wrote:
>>> Hmmmm ... not sure.  It seems a bit scary, but on the other hand we
>>> should be able to assume that the updating subtransaction hasn't been
>>> rolled back (else surely we shouldn't be firing the trigger).  So in
>>> principle it seems like the t_ctid link can't have been replaced.
>>> This will foreclose any ideas about collapsing t_ctid link chains,
>>> if anyone had it in mind to do that.
>>
>> Don't we already do that when pruning HOT chains?
>
> I thought that only happens after the transaction is committed, and
> old enough, whereas the trigger code only needs to follow the chain in
> the updating transaction.

Hmm, true.

I worry a bit that this might foreclose possible future optimization
of the "self update" case, which is a known pain point.  Am I wrong to
worry?

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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