Now that I have a little time to work on this again, I've thought about it
and it seems that an easy and somewhat accurate cop-out to do this is to
use whatever the selectivity function would be for the like operator,
multiplied by a scalar that pg_tgrm should already have access to.
Unfortunately, it's not at all clear to me from reading
http://www.postgresql.org/docs/8.1/interactive/xoper-optimization.html#AEN33077
how like impliments selectivity. Any pointers on where to look?
On Wed, 4 Oct 2006, Tom Lane wrote:
Ben <bench@xxxxxxxxxxxxxxx> writes:
How can I get the planner to not expect so many rows to be returned?
Write an estimation function for the pg_trgm operator(s). (Send in a
patch if you do!) I see that % is using "contsel" which is only a stub,
and would likely be wrong for % even if it weren't.
A possibly related question is: because pg_tgrm lets me set the
matching threshold of the % operator, how does that affect the planner?
It hasn't a clue about that.
regards, tom lane
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