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List:       pgsql-performance
Subject:    Re: [PERFORM] regression ? 8.4 do not apply One-Time Filter to
From:       Robert Haas <robertmhaas () gmail ! com>
Date:       2009-07-22 18:19:52
Message-ID: 603c8f070907221119v63b9efe5rcb2cd5a251640c8d () mail ! gmail ! com
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On Wed, Jul 1, 2009 at 8:08 PM, Sergey Burladyan<eshkinkot@gmail.com> wrote:
> 
> 8.4 from CVS HEAD:
> EXPLAIN ANALYZE select * from (select n, 1 as r from generate_series(1, 100000) as \
> n union all select n, 2 from generate_series(1, 100000) as n) as x where r = 3; \
>                 QUERY PLAN
> --------------------------------------------------------------------------------------------------------------------------------
>  Result  (cost=0.00..30.00 rows=10 width=36) (actual time=90.723..90.723 rows=0 \
>                 loops=1)
> ->  Append  (cost=0.00..30.00 rows=10 width=36) (actual time=90.720..90.720 rows=0 \
>                 loops=1)
> ->  Function Scan on generate_series n  (cost=0.00..15.00 rows=5 width=36) (actual \
>                 time=45.191..45.191 rows=0 loops=1)
> Filter: (1 = 3)
> ->  Function Scan on generate_series n  (cost=0.00..15.00 rows=5 width=36) (actual \
>                 time=45.522..45.522 rows=0 loops=1)
> Filter: (2 = 3)
> Total runtime: 118.709 ms
> (7 rows)
> 
> 8.3.7:
> EXPLAIN ANALYZE select * from (select n, 1 as r from generate_series(1, 100000) as \
> n union all select n, 2 from generate_series(1, 100000) as n) as x where r = 3; \
>                 QUERY PLAN
> ----------------------------------------------------------------------------------------------------------
>  Result  (cost=0.00..25.02 rows=2 width=8) (actual time=0.005..0.005 rows=0 \
>                 loops=1)
> ->  Append  (cost=0.00..25.02 rows=2 width=8) (actual time=0.004..0.004 rows=0 \
>                 loops=1)
> ->  Result  (cost=0.00..12.50 rows=1 width=4) (actual time=0.001..0.001 rows=0 \
> loops=1) One-Time Filter: false
> ->  Function Scan on generate_series n  (cost=0.00..12.50 rows=1 width=4) (never \
>                 executed)
> ->  Result  (cost=0.00..12.50 rows=1 width=4) (actual time=0.000..0.000 rows=0 \
> loops=1) One-Time Filter: false
> ->  Function Scan on generate_series n  (cost=0.00..12.50 rows=1 width=4) (never \
> executed) Total runtime: 0.053 ms
> (9 rows)
> 
> Is it right ?

This might be related to this fix by Tom.

http://archives.postgresql.org/message-id/20090711040933.7A08375331E@cvs.postgresql.org


...Robert

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