Carmen,
Regrettably I can't tell you what SUN's buffer or read ahead size is, but I
dealt with that issue on our HP's some years ago & the result can be
"interesting" to say the least. On the HP-UX platform they allow you up to 32K
of data in a single time slice or read. Basically it means that you can read
32K of data before you have to release the CPU to another process & wait for
your turn again. Therefore, once you find that value divide it by your block
size & you have the largest setting for DB_FILE_MULTIBLOCK_READ_COUNT that will
work in your instance. Setting it larger has no effect, at least on HP, as your
request gets truncated. (IE, you can ask for 64K but all you'll get is 32K).
Setting it smaller may on some systems cause a waste of IO resources. BUT in
any case setting it one way or the other affects the cost based optimizer.
Example, in a test instance I tried setting DB_FILE_MULTIBLOCK_READ_COUNT =1000.
The DB ran just fine, but CBO would never use an index. I then tried
DB_FILE_MULTIBLOCK_READ_COUNT = 1. Again the DB ran OK, but CBO almost never
wanted to do a full table scan.
Dick Goulet
____________________Reply Separator____________________
Author: "Carmen Rusu" <[EMAIL PROTECTED]>
Date: 6/12/2002 5:53 AM
Kevin Loney's Oracle8i DBA Handbook says you need to know the "operating
system's I/O buffer size" in order to set the init param
DB_FILE_MULTIBLOCK_READ_COUNT correctly.
What is the definition of "operating system's I/O buffer size Loney is talking
about?
What is the value of " I/O buffer size" for SunOS 5.8?
Went to Sun's web site and got lost...I just want two straight answers to my two
questions.
Thanks,
Carmen Rusu
Sr Oracle DBA
512-463-3657 (office)
512-606-5012 (pager)
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