Re: Adding TEXT columns tanks performance? - Mailing list pgsql-general

From Tom Lane
Subject Re: Adding TEXT columns tanks performance?
Date
Msg-id 18694.1171128860@sss.pgh.pa.us
Whole thread Raw
In response to Re: Adding TEXT columns tanks performance?  (Arturo Perez <aperez@hayesinc.com>)
Responses Re: Adding TEXT columns tanks performance?  (Arturo Perez <aperez@hayesinc.com>)
Re: Adding TEXT columns tanks performance?  (Arturo Perez <aperez@hayesinc.com>)
List pgsql-general
Arturo Perez <aperez@hayesinc.com> writes:
> Saturday I changed a table to add a varchar(24) and a TEXT column.

You didn't actually say which of these tables you changed?

> I'm not very good at reading these but it looks like sort memory might
> be too low?

The runtime seems to be entirely in the index scan on user_tracking.
I'm surprised it doesn't do something to avoid a full-table indexscan
--- in this case, hashing with extended_user as the inner relation would
seem like the obvious thing.  Is user_id a hashable datatype?

It's possible that adding the columns would have affected the plan by
making it look like a sort or hash would take too much memory, but if
that were it then your hand increase in work_mem should have fixed it.
Tis odd.  I don't suppose you know what plan was used before?

            regards, tom lane

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