From: Robert Haas <robertmhaas@gmail.com>
To: Greg Stark <stark@enterprisedb.com>
Cc: Greg Smith <gsmith@gregsmith.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: ITAGAKI Takahiro <itagaki.takahiro@oss.ntt.co.jp>
Cc: Postgres <pgsql-hackers@postgresql.org>
Subject: Re: posix_fadvise v22
Date: Fri, 2 Jan 2009 20:42:51 -0500
Message-ID: <603c8f070901021742s61dcbaf2r51deff1219196944@mail.gmail.com> (raw)
In-Reply-To: <4136ffa0901021502w78f0611dx63929ac0fbbdc2f4@mail.gmail.com>
References: <FDDBA24E-FF4D-4654-BA75-692B3BA71B97@enterprisedb.com>
<8347.1229012970@sss.pgh.pa.us>
<4136ffa0812110911x4914a951o6ca502879e3dede7@mail.gmail.com>
<87k5a6tmy7.fsf@oxford.xeocode.com>
<603c8f070901011230t1afa6644racb715b975078054@mail.gmail.com>
<10658.1230843315@sss.pgh.pa.us>
<603c8f070901011843p121e40afu35c4a7bdc51c051c@mail.gmail.com>
<Pine.GSO.4.64.0901020335150.16680@westnet.com>
<603c8f070901021436v71f10188g1d747b493c89f2f5@mail.gmail.com>
<4136ffa0901021502w78f0611dx63929ac0fbbdc2f4@mail.gmail.com>
> Hm, what were those plans? You might want to put the old code back in
> explain.c to print the prefetching target to see how well it's doing.
Well, bad news. Here's one where prefetching seems to make it WORSE.
rhaas=# explain select sum(1) from enormous where l_shipdate in
('1992-01-01', '1993-01-01', '1994-01-01', '1995-01-01', '1996-01-01',
'1997-01-01', '1998-01-01', '1999-01-01', '2000-01-01', '2001-01-01');
QUERY PLAN
--------------------------------------------------------------------------------------------------------------------------------------------------------------
------------
Aggregate (cost=455072.75..455072.76 rows=1 width=0)
-> Bitmap Heap Scan on enormous (cost=3327.59..454634.09
rows=175464 width=0)
Recheck Cond: (l_shipdate = ANY
('{1992-01-01,1993-01-01,1994-01-01,1995-01-01,1996-01-01,1997-01-01,1998-01-01,1999-01-01,2000-01-01,2001-01-01}'::d
ate[]))
-> Bitmap Index Scan on enormous_l_shipdate
(cost=0.00..3283.72 rows=175464 width=0)
Index Cond: (l_shipdate = ANY
('{1992-01-01,1993-01-01,1994-01-01,1995-01-01,1996-01-01,1997-01-01,1998-01-01,1999-01-01,2000-01-01,2001-01-01}
'::date[]))
(5 rows)
With effective_io_concurrency set to 1, this took 32 s. With
effective_io_concurrency set to 4, it took 50 s. The table was
created like this:
create table enormous as select l.*, l_instance from lineitem l,
generate_series(1, 8) l_instance;
create index enormous_l_shipdate on enormous (l_shipdate);
vacuum analyze enormous;
...where lineitem is from the skewed TPC-H data for the histojoin patch.
...Robert
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To: pgsql-hackers@postgresql.org
Cc: robertmhaas@gmail.com, stark@enterprisedb.com, gsmith@gregsmith.com, tgl@sss.pgh.pa.us, itagaki.takahiro@oss.ntt.co.jp
Subject: Re: posix_fadvise v22
In-Reply-To: <603c8f070901021742s61dcbaf2r51deff1219196944@mail.gmail.com>
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