From: Tom Lane <tgl@sss.pgh.pa.us>
To: Greg Smith <gsmith@gregsmith.com>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: Gregory Stark <stark@enterprisedb.com>
Cc: ITAGAKI Takahiro <itagaki.takahiro@oss.ntt.co.jp>
Cc: Postgres <pgsql-hackers@postgresql.org>
Subject: Re: posix_fadvise v22
Date: Fri, 02 Jan 2009 10:33:25 -0500
Message-ID: <24481.1230910405@sss.pgh.pa.us> (raw)
In-Reply-To: <Pine.GSO.4.64.0901020335150.16680@westnet.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>
Greg Smith <gsmith@gregsmith.com> writes:
> On Thu, 1 Jan 2009, Robert Haas wrote:
>> The only thing I haven't been able to do is demonstrate that this change
>> actually produces a performance improvement. Either I'm testing the
>> wrong thing, or it just doesn't provide any benefit on a single-spindle
>> system.
> When I did a round of testing on the earlier prefetch test program Greg
> Stark put together, one of my single-spindle Linux system didn't show any
> real benefit. So as long as you didn't see performance degrade, your not
> seeing any improvement isn't bad news.
ISTM that you *should* be able to see an improvement on even
single-spindle systems, due to better overlapping of CPU and I/O effort.
If the test case is either 100% CPU-bound or 100% I/O-bound then no,
but for anything in between there ought to be improvement.
regards, tom lane
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To: pgsql-hackers@postgresql.org
Cc: tgl@sss.pgh.pa.us, gsmith@gregsmith.com, robertmhaas@gmail.com, stark@enterprisedb.com, itagaki.takahiro@oss.ntt.co.jp
Subject: Re: posix_fadvise v22
In-Reply-To: <24481.1230910405@sss.pgh.pa.us>
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