| From: | "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov> |
|---|---|
| To: | <tgl(at)sss(dot)pgh(dot)pa(dot)us>, <bruno(at)wolff(dot)to> |
| Cc: | <linux(at)alteeve(dot)com>, <john(at)arbash-meinel(dot)com>, <tobias(at)nordicbet(dot)com>, <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: Index ot being used |
| Date: | 2005-06-13 16:46:46 |
| Message-ID: | s2ad7232.064@gwmta.wicourts.gov |
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| Thread: | |
| Lists: | pgsql-performance |
I agree that ignoring useless columns in an ORDER BY clause is less
important than ignoring index columns where the value is fixed. There
is one use case for ignoring useless ORDER BY columns that leaps to
mind, however -- a column is added to the ORDER BY clause of a query to
help out the optimizer, then the indexes are modified such that that
column is no longer useful. Whether this merits the programming effort
and performance hit you describe seems highly questionable, though.
-Kevin
>>> Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> 06/13/05 11:22 AM >>>
I don't think the use-case has been shown that justifies doing this much
work to ignore useless ORDER BY clauses. The examples that have come up
in the past all suggest ignoring index columns not the other way 'round.
Can you make a case that we need to do that part of it?
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