From: | Bernhard Weisshuhn <bkw(at)weisshuhn(dot)de> |
---|---|
To: | pgsql-general(at)postgresql(dot)org |
Subject: | Re: cyclical redundancy checksum algorithm(s)? |
Date: | 2006-09-28 08:55:35 |
Message-ID: | 451B8E07.5010505@weisshuhn.de |
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Thread: | |
Lists: | pgsql-general |
Joachim Wieland schrieb:
> On Thu, Sep 28, 2006 at 07:09:43AM +0100, John Sidney-Woollett wrote:
>> Why not use an update trigger on the affected tables to record a
>> lastupdated timestamp value when the record is changed.
>
>> Surely this is simpler thanks computing some kind of row hash?
>
> It depends on how you define "change". With the triggers you propose an
>
> UPDATE table SET col = col;
>
> is a change because there was a write operation. Any hash function's output
> would be "no change" because the actual data did not change. An update might
> entail an expensive update of some external data so you might want to make
> sure that data really got modified.
>
You can always compare the old and new values in the trigger function to
detect that kind of non-update.
bkw
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