Karl Wright <kwright@xxxxxxxxxxxxx> writes: > [2007-06-18 09:39:49,797]ERROR Plan: Index Scan using i1181764142395 on > intrinsiclink (cost=0.00..14177.29 rows=5 width=253) > [2007-06-18 09:39:49,797]ERROR Plan: Index Cond: ((jobid = $2) AND > ((childidhash)::text = ($3)::text)) > [2007-06-18 09:39:49,797]ERROR Plan: Filter: ((childid = ($4)::text) > AND ((isnew = ($5)::bpchar) OR (isnew = ($6)::bpchar))) >> In this case it looks like the planner is afraid that that's exactly >> what will happen --- a cost of 14177 suggests that several thousand row >> fetches are expected to happen, and yet it's only predicting 5 rows out >> after the filter. > Well, that's odd, because the hash in question that it is using is the > SHA-1 hash of a URL. There's essentially one row per URL in this table. What about isnew? Also, how many rows do *you* expect out of the query? The planner is not going to be aware of the hashed relationship between childidhash and childid --- it'll think those are independent conditions which they evidently aren't. So it may be that the query really does retrieve thousands of rows, and the rows=5 estimate is bogus because it's double-counting the selectivity of the childid condition. regards, tom lane
