Re: Optimising "in" queries

I thought that I had but I screwed up the addresses.
Here they are:

benparts=# explain select count(rdate),rdate from reading where
sensor_id in (1137,1138,1139,1140) group by rdate order by rdate desc
limit 1;
QUERY PLAN
---------------------------------------------------------------------------------------------------
Limit (cost=0.00..39890.96 rows=1 width=8)
-> GroupAggregate (cost=0.00..7938300.21 rows=199 width=8)
-> Index Scan Backward using date on reading
(cost=0.00..7937884.59 rows=82625 width=8)
Filter: (sensor_id = ANY
('{1137,1138,1139,1140}'::integer[]))
(4 rows)

benparts=# explain select count(rdate),rdate from reading where
sensor_id in (1137,1138,1139) group by rdate order by rdate desc limit
1;
QUERY PLAN
-----------------------------------------------------------------------------------------------------
Limit (cost=48364.32..48364.32 rows=1 width=8)
-> Sort (cost=48364.32..48364.49 rows=69 width=8)
Sort Key: rdate
-> HashAggregate (cost=48361.35..48362.21 rows=69 width=8)
-> Bitmap Heap Scan on reading (cost=535.53..48218.10
rows=28650 width=8)
Recheck Cond: (sensor_id = ANY
('{1137,1138,1139}'::integer[]))
-> Bitmap Index Scan on reading_sensor
(cost=0.00..528.37 rows=28650 width=0)
Index Cond: (sensor_id = ANY
('{1137,1138,1139}'::integer[]))
(8 rows)

benparts=# explain analyze select count(rdate),rdate from reading where
sensor_id in (1137,1138,1139) group by rdate order by rdate desc limit
1;

QUERY PLAN
---------------------------------------------------------------------------------------------------------------------------------------------------------
Limit (cost=49260.20..49260.20 rows=1 width=8) (actual
time=3263.219..3263.221 rows=1 loops=1)
-> Sort (cost=49260.20..49260.38 rows=73 width=8) (actual
time=3263.213..3263.213 rows=1 loops=1)
Sort Key: rdate
-> HashAggregate (cost=49257.03..49257.94 rows=73 width=8)
(actual time=3049.667..3093.345 rows=30445 loops=1)
-> Bitmap Heap Scan on reading (cost=541.97..49109.62
rows=29481 width=8) (actual time=1727.021..2908.563 rows=91334 loops=1)
Recheck Cond: (sensor_id = ANY
('{1137,1138,1139}'::integer[]))
-> Bitmap Index Scan on reading_sensor
(cost=0.00..534.60 rows=29481 width=0) (actual time=1714.980..1714.980
rows=91334 loops=1)
Index Cond: (sensor_id = ANY
('{1137,1138,1139}'::integer[]))
Total runtime: 3264.121 ms
(9 rows)

benparts=# explain analyze select count(rdate),rdate from reading where
sensor_id in (1137,1138,1139,1140) group by rdate order by rdate desc
limit 1;
QUERY
PLAN
---------------------------------------------------------------------------------------------------------------------------------------------
Limit (cost=0.00..41959.54 rows=1 width=8) (actual time=1.284..1.285
rows=1 loops=1)
-> GroupAggregate (cost=0.00..8182110.32 rows=195 width=8) (actual
time=1.281..1.281 rows=1 loops=1)
-> Index Scan Backward using date on reading
(cost=0.00..8181711.41 rows=79294 width=8) (actual time=1.254..1.261
rows=2 loops=1)
Filter: (sensor_id = ANY
('{1137,1138,1139,1140}'::integer[]))
Total runtime: 1.360 ms
(5 rows)

On Friday 24 August 2007 05:16, Alvaro Herrera wrote:
<snip>
> I don't think you showed us the EXPLAIN ANALYZE results that Scott
> requested.

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