From: | John Sidney-Woollett <johnsw(at)wardbrook(dot)com> |
---|---|
To: | Joachim Wieland <joe(at)mcknight(dot)de> |
Cc: | Karen Hill <karen_hill22(at)yahoo(dot)com>, pgsql-general(at)postgresql(dot)org |
Subject: | Re: cyclical redundancy checksum algorithm(s)? |
Date: | 2006-09-28 08:43:13 |
Message-ID: | 451B8B21.60602@wardbrook.com |
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Thread: | |
Lists: | pgsql-general |
Ah, good point! Missed the subtlety of what was being asked.
John
Joachim Wieland wrote:
> 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.
>
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