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Re: Compressing the AFTER TRIGGER queue

From: Dean Rasheed <dean(dot)a(dot)rasheed(at)gmail(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Compressing the AFTER TRIGGER queue
Date: 2011-08-01 17:00:00
Message-ID: CAEZATCW5A47-hog46kOwtSXJf-fwkQfmnVp=OfiS_53B85bH_A@mail.gmail.com (view raw or flat)
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On 1 August 2011 17:49, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Dean Rasheed <dean(dot)a(dot)rasheed(at)gmail(dot)com> writes:
>> I've been thinking some more about the long-standing problem of the
>> AFTER TRIGGER queue using too much memory, and I think that the
>> situation can be improved by using some basic compression.
>
>> Currently each event added to the AFTER TRIGGER queue uses 10 bytes
>> per trigger per row for INSERTs and DELETEs, and 16 for UPDATEs. The
>> attached patch reduces this down to just 1 byte in a number of common
>> cases.
>
> Ummm ... I only read the data structure comments, not the code, but I
> don't see where you store the second CTID for an update event?
>

Ah yes, I forgot to mention that bit. I'm using
&(tuple1.t_data->t_ctid) to get the second CTID from the old tuple. Is
that safe? As far as I could see, this would match the new tuple after
a heap update.

Regards,
Dean

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