2010/11/21 Humair Mohammed <humairm@hotmail.com>:
>
> 1) OS/Configuration
> 64-bit Windows 7 Enterprise with 8G RAM and a Dual Core 2.67 Ghz Intel CPU
> postgresql-x64-9.0 (PostgreSQL 9.0.1, compiled by Visual C++ build 1500,
> 64-bit)
> work_mem 2GB
> shared_buffers = 2
shared_buffers = 2 ???
Regards
Pavel Stehule
> 2) Dataset
> name,pages,tuples,pg_size_pretty
> "pivotbad";1870;93496;"15 MB"
> "pivotgood";5025;251212;"39 MB"
> 3) EXPLAIN (ANALYZE ON, BUFFERS ON)
> "Hash Join (cost=16212.30..52586.43 rows=92869 width=17) (actual
> time=25814.222..32296.765 rows=3163 loops=1)"
> " Hash Cond: (((pb.id)::text = (pg.id)::text) AND ((pb.question)::text =
> (pg.question)::text))"
> " Join Filter: ((COALESCE(pb.response, 'MISSING'::character varying))::text
> <> (COALESCE(pg.response, 'MISSING'::character varying))::text)"
> " Buffers: shared hit=384 read=6511, temp read=6444 written=6318"
> " -> Seq Scan on pivotbad pb (cost=0.00..2804.96 rows=93496 width=134)
> (actual time=0.069..37.143 rows=93496 loops=1)"
> " Buffers: shared hit=192 read=1678"
> " -> Hash (cost=7537.12..7537.12 rows=251212 width=134) (actual
> time=24621.752..24621.752 rows=251212 loops=1)"
> " Buckets: 1024 Batches: 64 Memory Usage: 650kB"
> " Buffers: shared hit=192 read=4833, temp written=4524"
> " -> Seq Scan on pivotgood pg (cost=0.00..7537.12 rows=251212
> width=134) (actual time=0.038..117.780 rows=251212 loops=1)"
> " Buffers: shared hit=192 read=4833"
> "Total runtime: 32297.305 ms"
> 4) INDEXES
> I can certainly add an index but given the table sizes I am not sure if that
> is a factor. This by no means is a large dataset less than 350,000 rows in
> total and 3 columns. Also this was just a quick dump of data for comparison
> purpose. When I saw the poor performance on the COALESCE, I pointed the data
> load to SQL Server and ran the same query except with the TSQL specific
> ISNULL function.
>
