Re: Slow update

Marc Mamin wrote:

> Hello,
>
> - did you vacuum your tables recently ?
>
> - What I miss in your query is a check for the rows that do not need
> to be udated:
>
> AND NOT (service = b.service
> AND status = b.status
> AND has_notification = gateway_id NOT IN (4,101,102)
> AND operator = COALESCE( b.actual_target_network_id,
> b.requested_target_network_id )
>
>
> depending on the fraction of rows that are already up to date, the
> might fasten your process quite a lot...
I don't see why it would. As far as I know, the high saving in update
time is done by using the indices. All the other conditions that are not
on indices are all checked using a sequential scan on the rows that were
brought from the index, so adding more conditions wouldn't make this a
lot faster - maybe even slower because more comparisons are made.

In any case, the logic of the database is that the records that have
delivered = 0 are always a subset of the records that are changed in
this query, so querying on delivered=0 - which is an indexed query -
actually make the above redundant.

Thanks for your response,
Herouth