Re: cyclical redundancy checksum algorithm(s)? - Mailing list pgsql-general

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.

--
Joachim Wieland                                              joe@mcknight.de
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