Re: vacuum, performance, and MVCC

The world rejoiced as tgl@sss.pgh.pa.us (Tom Lane) wrote:
> Lukas Smith <smith@pooteeweet.org> writes:
>> Jochem van Dieten wrote:
>>> make the session handler smarter? And if you can't do that, put some
>>> logic in the session table that turns an update without changes into a
>>> no-op?
>
>> err isnt that one the job of the database?
>
> No.  That idea has been suggested and rejected before.  Detecting
> that an UPDATE is a no-op would require a significant number of
> cycles, and in most applications, most or all of the time those
> cycles would be wasted effort.  If you have a need for this
> behavior, you can attach a BEFORE UPDATE trigger to a table that
> checks for all-fields-the-same and suppresses the update.  I don't
> think that should be automatic though.

If this be handled via a stored procedure, the stored proc could hide
this detail nice and completely...
 select store_session(a,b,c,d,e);

store_session can be quite smart enough to not bother doing spurious
updates.
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