Date: Wed, 16 Jan 2002 23:53:07 +0100 From: "Rogier R. Mulhuijzen" <drwilco@drwilco.net> To: jgrosch@mooseriver.com, hackers@FreeBSD.ORG Cc: freebsd-questions@FreeBSD.ORG Subject: Re: [nicole@unixgirl.com: What is biord?] Message-ID: <5.1.0.14.0.20020116233750.02874e18@mail.drwilco.net> In-Reply-To: <20020116141825.A45998@mooseriver.com>
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>
> Hello
> I have a mysql database that seems slow and when looking at it in top it
>always seems to be in a state of biord
> What the heck is biord I can't find this anywere
>
> Thanks
Block I/O ReaD (if I'm not terribly mistaken. I'm thinking it could be Buf
IO too, but that would be confusing to the layman =) )
Basically it's doing a lot of read IO or your disks are very slow.
Which is not a big surprise because databases normally spend a lot of time
in disk IO.
I'm not up to speed on MySQL tuning, but I've done a fair amount of Oracle
tuning, and there's two approaches that can be taken:
1) lessen the amount of IO.
2) make the IO faster.
Making it faster can be the most expensive in money (buying SCSI RAID
arrays), and not always as effective.
Lessening the IO is usually a little more costly in the time department,
but can be a LOT more effective.
When lessening the IO, again there are mainly 2 things to be done.
1) have more blocks buffered.
2) make queries use less blocks
More buffering is an easy fix on a machine with lots of memory. I am not
familiar with MySQL's internals, but Oracle uses its own buffercache
(optimized for RDBMS usage) and you can specify how big that should
be. When a machine has 512megs of RAM and the database is the only thing
on the machine, making the buffers take up half of that is not a silly
thing at all. (You wont believe how often I come across machines that are
ill configured that way. HUGE amount of RAM, and only 5% is used...)
Making queries use less blocks is the hardest part, but a lot of the times
placing indexes on columns that are used in joins or in WHERE clauses can
make a huge difference. Also not using too many tables in a single query
helps (eliminate wannahave columns in favor of faster musthave results).
You could always find some MySQl guru's of course =)
I hope this sheds a little light on the subject,
DocWilco
P.S.: this really belongs on freebsd-questions@freebsd.org so I'm cross
posting this answer there
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