On 7.4 RC2, I'm seeing a case where the query planner estimates are way out of line after grouping the result of a union. I've tried adjusting the statistics targets up to 200, and it made no difference in the planner's estimates. The point of the full query this came from is that it also has an aggregate function that produces a space-delimited list of commodity & fak for each id. Does anyone have any suggestions on tweaks to apply or ways to rewrite this? Is this one of those ugly corners where the query planner doesn't have a clue how to estimate this (seeing the nice round 200 estimate makes me suspicious)?
EXPLAIN ANALYZE SELECT id FROM (SELECT id, commodity FROM commodities WHERE commodity IS NOT NULL UNION SELECT id, fak FROM commodities WHERE fak IS NOT NULL ) all_commodities GROUP BY id; QUERY PLAN ---------------------------------------------------------------------------------------------------------------------------------------------------------------- HashAggregate (cost=15939.16..15939.16 rows=200 width=4) (actual time=3537.281..3680.418 rows=83306 loops=1) -> Subquery Scan all_commodities (cost=14002.00..15697.02 rows=96858 width=4) (actual time=2268.052..3214.996 rows=95715 loops=1) -> Unique (cost=14002.00..14728.44 rows=96858 width=15) (actual time=2268.043..2881.688 rows=95715 loops=1) -> Sort (cost=14002.00..14244.15 rows=96858 width=15) (actual time=2268.037..2527.083 rows=100008 loops=1) Sort Key: id, commodity -> Append (cost=0.00..5034.42 rows=96858 width=15) (actual time=7.402..1220.320 rows=100008 loops=1) -> Subquery Scan "*SELECT* 1" (cost=0.00..2401.23 rows=36831 width=15) (actual time=7.398..590.004 rows=39772 loops=1) -> Seq Scan on commodities (cost=0.00..2032.92 rows=36831 width=15) (actual time=7.388..468.415 rows=39772 loops=1) Filter: (commodity IS NOT NULL) -> Subquery Scan "*SELECT* 2" (cost=0.00..2633.19 rows=60027 width=14) (actual time=0.016..408.160 rows=60236 loops=1) -> Seq Scan on commodities (cost=0.00..2032.92 rows=60027 width=14) (actual time=0.010..221.635 rows=60236 loops=1) Filter: (fak IS NOT NULL) Total runtime: 3783.009 ms (13 rows) ---------------------------(end of broadcast)--------------------------- TIP 1: subscribe and unsubscribe commands go to [EMAIL PROTECTED]