Tom Lane wrote:
Jack Orenstein <jack.orenstein@xxxxxxx> writes:
Tom Lane wrote:
If you plug in a value that *does* occur in the table it should probably
choose the more-relevant index consistently.
Unfortunately, it matters a lot at runtime. The dh value is not very selective,
as shown by the statistics above.
A dh value that does not occur in the index is *perfectly* selective.
I'm not sure what your problem is but this example isn't illustrating
anything wrong that I can see.
I see your point.
I may have simplified too far. Our application runs a number of different
queries. All our WHERE clauses restrict dh and fh. For a given pair of (dh, fh)
values, the initial query should come up empty and then insert this pair, and
then there is further processing (SELECT, UPDATE). Something is causing a huge
number of index row reads (according to pg_stat_user_indexes) but only in tables
that have been vacuumed.
Jack
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