I thought the benefits were from skipping the read-ahead logic.
What was seen prior to the implementation of directio was this:
- System running a high(er) load. It was difficult to see why the
load was higher, as oracle was the primary process(es).
After the implementation, the load on the server dropped from a load
of ~6 (on a 6 way box) to a load of 1.5 to 2. The system 'felt'
faster, as well.
It should be noted that traditional filesystem access (creating
tables, etc.) dropped in performance by a factor of about 10. Again,
I attributed this to the lack of a read ahead capability. Luckily,
creating new database tables is a relatively infrequent event.
Does anybody else have any other points on this?
On May 12, 2006, at 12:53 AM, Roch Bourbonnais - Performance
Engineering wrote:
From: Gregory Shaw <[EMAIL PROTECTED]>
Sender: [EMAIL PROTECTED]
To: Mike Gerdts <[EMAIL PROTECTED]>
Cc: ZFS filesystem discussion list <zfs-discuss@opensolaris.org>,
[EMAIL PROTECTED]
Subject: Re: [zfs-discuss] ZFS and databases
Date: Thu, 11 May 2006 13:15:48 -0600
Regarding directio and quickio, is there a way with ZFS to skip the
system buffer cache? I've seen big benefits for using directio when
the data files have been segregated from the log files.
Were the benefits coming from extra concurrency (no
single writter lock) or avoiding the extra copy to page cache or
from too much readahead that is not used before pages need to
be recycled.
ZFS already has the concurrency.
The page cache copy is really rather cheap and I assert
somewhat necessary to insure data integrity
The extra readahead is somewhat of a bug in UFS (read 2
pages get a maxcontig chunk (1MB)).
ZFS is new, conventional wisdom, may or may not apply.
-r
-----
Gregory Shaw, IT Architect
Phone: (303) 673-8273 Fax: (303) 673-8273
ITCTO Group, Sun Microsystems Inc.
1 StorageTek Drive ULVL4-382 [EMAIL PROTECTED] (work)
Louisville, CO 80028-4382 [EMAIL PROTECTED] (home)
"When Microsoft writes an application for Linux, I've Won." - Linus
Torvalds
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