Re: Index Tuning Features - Mailing list pgsql-hackers

From Tom Lane
Subject Re: Index Tuning Features
Date
Msg-id 25108.1160496373@sss.pgh.pa.us
Whole thread Raw
In response to Index Tuning Features  (Simon Riggs <simon@2ndquadrant.com>)
Responses Re: Index Tuning Features  (Robert Treat <xzilla@users.sourceforge.net>)
Re: Index Tuning Features  ("Mark Woodward" <pgsql@mohawksoft.com>)
List pgsql-hackers
Simon Riggs <simon@2ndquadrant.com> writes:
> - Virtual Indexes

> An index which only exists in the catalog, so is visible to the planner
> but not the executor.

Say what?  What would that possibly be useful for, other than crashing
any bit of code that failed to know about it?

> - RECOMMEND command

> Similar in usage to an EXPLAIN, the RECOMMEND command would return a
> list of indexes that need to be added to get the cheapest plan for a
> particular query (no explain plan result though).

Both of these seem to assume that EXPLAIN results, without EXPLAIN
ANALYZE results to back them up, are sufficient for tuning.  I find
this idea a bit dubious, particularly for cases of "marginal" indexes.

> Specifically, multi-column indexes are not considered very heavily in
> RECOMMEND.

That seems like a bad idea as well --- multicol indexes are exactly the
sort of thing a novice DBA might fail to consider.  If you're going to
do this then you should consider all cases.
        regards, tom lane


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