*BSD News Article 71004


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From: peter@cyklop.volvo.se (peter hakanson)
Newsgroups: comp.unix.programmer,comp.os.linux.development.apps,comp.unix.solaris,comp.unix.bsd
Subject: Re: How to flush write buffer ?
Followup-To: comp.unix.programmer,comp.os.linux.development.apps,comp.unix.solaris,comp.unix.bsd
Date: 13 Jun 1996 15:39:50 GMT
Organization: Volvo Corp.
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This is the reason that databases should be run on raw-devices (and
not on filesystems)

Oracle used to have this possibility. There was also a performance
gain (since oracle buffers internally, having a second 
buffer cache will waist cpu cycles )

peter håkanson
Shankar Unni (shankar@chromatic.com) wrote:
: Hugh McCurdy wrote:

: > I must be using "logically" incorrectly or something.  To me a
: > "logical write" would be a write that would allow other processes to
: > have access to the data written.

: Absolutely. And even for buffered writes, almost all systems really *do*
: treat the buffers as if they were a cache; i.e. if one program writes
: the file (but the stuff is still in kernel buffers), and another program
: requests a read from that file, the kernel will return the buffer
: contents, not the disk contents.

: The main reason for *synchronous* writes is to avoid problems with
: system crashes and the like, where the kernel buffers are *not* written
: back correctly.

: For instance, many OSes do asynchronous writes for ordinary files by
: default, but synchronous writes for *directory* updates, because those
: data structures are sensitive, and an incorrect or partial directory
: update can *really* screw up your file system..

: Typical candidates for synchronous writes (or at least, a synchronizing
: operation) are database transactions (where you want to atomically
: commit a transaction with some guarantee of completion), directory
: updates, etc.
: -- 
: Shankar Unni                                  shankar@chromatic.com
: Chromatic Research                            (408) 752-9488

--
--
Peter Hakanson  VolvoData Dep 2580 phone +46 31 66 74 27