Path: utzoo!attcan!uunet!husc6!uwvax!rutgers!cmcl2!nrl-cmf!ames!ncar!noao!nud!anasaz!john
From: john@anasaz.UUCP (John Moore)
Newsgroups: comp.databases
Subject: Re: ensuring output has reached the disc (was Oracle wars)
Summary: Raw Device - Optimization?
Keywords: O_SYNC, fsync, SunOS 3.x
Message-ID: <1132@anasaz.UUCP>
Date: 22 Jul 88 20:39:08 GMT
References: <32133@pyramid.pyramid.com%
Reply-To: john@anasaz.UUCP (John Moore)
Organization: Anasazi Inc, Phoenix AZ
Lines: 22

In article <32133@pyramid.pyramid.com% eric@pyrps5.UUCP (Eric Bergan) writes:
%In article <179@quintus.UUCP> ok@quintus.UUCP (Richard A. O'Keefe) writes:
%>In article <302@infmx.UUCP> aland@infmx.UUCP (Alan S. Denney @ Informix)
%>writes:
%maintaining a per file descriptor list of dirty blocks. Raw disk just
%skips the file system code entirely, which provides you guarenteed
%contiguous disk space, and also no worries about indirect blocks. But
%the DBMS code has to do the disk management (what blocks are used, which

On a couple of machines, we have observed that raw device I/O does
not seem to have seek optimization and has extreme unfairness between
processes (one process gets lots of I/O's, another gets none, when
both are same priority and doing the same thing). Apparently the
raw devicer driver sends only one request at a time to the strategy
routine, and waits for it to finish before sending another, thus
defeating the seek optimization. Does anyone know how common this
is and which systems do provide optimization on raw devices?
-- 
John Moore (NJ7E)           {decvax, ncar, ihnp4}!noao!mcdsun!nud!anasaz!john
(602) 861-7607 (day or eve) {gatech, ames, rutgers}!ncar!...
The opinions expressed here are obviously not mine, so they must be
someone else's.