Am Donnerstag, 6. März 2008 schrieb Tom Lane: > What I propose doing about this is a small variant on Peter's original > suggestion: compute the estimated selectivity for > col = 'prefix' > and clamp the result of prefix_selectivity to be at least that.
OK, first results with this patch are in: The selectivity estimations are adjusted nicely, but the cost calculation doesn't change at all. Before: Index Scan using foo_idx_3 on foo foo (cost=0.01..6.03 rows=1 width=8) After: Index Scan using foo_idx_3 on foo foo (cost=0.01..6.03 rows=627 width=8) How is that possible? Btw., the corresponding query plan for the LIKE 'constant' case is: Index Scan using foo_idx_3 on foo foo (cost=0.00..2527.84 rows=627 width=8) This is what we had hoped to get in the "after" case. -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
