VERITAS Storage Foundation 4.1 Oracle Administrator's Guide

Tuning Oracle Databases Prerelease 8 September 2005, 8:55am
414 VERITAS Storage Foundation for Oracle Administrator’s Guide
bypasses the file system cache to improve database performance. Memory pages normally
allocated to the file system cache can be allocated to the database buffer cache (SGA). With
Oracle9i, you can adjust the SGA size without shutting down the database.
Setting Oracle Block Reads During Sequential Scans
The DB_FILE_MULTIBLOCK_READ_COUNT parameter specifies the maximum number of
blocks Oracle reads in one I/O operation during a sequential scan. When the file system is created
on a striped volume, set this parameter to a value that is a multiple of the full stripe size divided by
DB_BLOCK_SIZE. Using a full stripe size allows the read operations to take advantage of the full
bandwidth of the striped disks during sequential table scan.
Set the DB_FILE_MULTIBLOCK_READ_COUNT to a value that is a multiple of
(read_pref_io*read_nstream)/DB_BLOCK_SIZE, but the value should not exceed the
value of max_direct_iosz/DB_BLOCK_SIZE.
Use the vxtunefs command to display the value of read_pref_io, read_nstream, and
max_direct_iosz, for example:
# vxtunefs /db01
The vxtunefs command displays output similar to the following:
Filesystem i/o parameters for /db01
read_pref_io = 65536
read_nstream = 4
read_unit_io = 65536
write_pref_io = 65536
write_nstream = 4
write_unit_io = 65536
pref_strength = 10
buf_breakup_size = 131072
discovered_direct_iosz = 262144
max_direct_iosz = 2097152
default_indir_size = 8192
Setting Slave Parameters
Quick I/O and ODM provide support for asynchronous I/O, eliminating the need for multiple
logwriter slaves or database writer slaves. This parameter is set to 0 by default.
It is not necessary to set the DBWR_IO_SLAVES settings if you are using Quick I/O. The number
of DBWR writer processes is set within DB_WRITER_PROCESSES, which performs asynchronous
I/O.