1. AnarGodjaev
http://anargodjaev.wordpress.com/
Tuning Physical IO
You can barely tune you system for best performance logical IO but it
doesnt mean your system will not make any physical IO from your Disk
Subsystem because you data is on the disk systems and of course you cannot
buy enough memory to store all your data in memory. Now we will going to
interested in pyhsical IO performance.
1- When creating a tablespace always be careful about defining “extent
management” and “segment space management” parameters. “extent management
local” parameter can have two distinct values. Local: stands for extent
management should be in datafile headers which is using bitmap lookup table
and far faster than Dictionary: extent management is done in system
tablespaces which has lower performance.
-- creating a tablescpace
-createtablespace<ts_name>
datafile'$home/oradata/<SID>/<dbf_name>.dbf'
size=10M
extent management local
segment space management AUTO;
create table <table_name> (<col_name>number) tablespace<ts_name>;
2- Be careful about your RAID levels
RAID Type of RaidControl_FileDatabase_FileRedo_LogArchive_Log
---- ------------------------ ------------- -------- ----------0 Striping Avoid OK AvoidAvoid
1 Shadowing Best OK Best Best
1+0 Striping and Shadowing OK Best Avoid Avoid
3 Striping with static parity OK OKAvoid Avoid
5 Striping with rotating parity OKBest(*) Avoid Avoid
(*) if RAID0-1 not available
3- You can examine file statistics
--- you can check file statistics
-select
t2.name,
t1.phyrds,
t1.phywrts,
t1.readtim,
t1.writetim
from
v$filestat t1,
v$datafile t2
where
t1.file#=t2.file#

2. AnarGodjaev
http://anargodjaev.wordpress.com/
order by phyrdsdesc, phywrtsdesc;
--- temporary statistics
-select
t2.name,
t1.phyrds,
t1.phywrts,
t1.readtim,
t1.writetim
from
v$tempstat t1,
v$tempfile t2
where
t1.file#=t2.file#
order by phyrdsdesc, phywrtsdesc;
4- Consider the following parameters for background processes performance
tuning. More than one dbwr(db writer process can be used)
If not asynchronous IO then
DBWR_IO_SLAVES = [1...9]
Else
DISK_ASYNCH_IO = [ON | OF]
End if
--- tuning dbwriter process
-select* from v$parameterwhere name like '%dbwr_io_slaves%';
select* from v$parameterwhere name like '%db_writer_processes%';
select* from v$parameterwhere name like '%disk_asynch_io%';
--alter system set db_writer_processes=[0...9];
alter system set db_writer_processes=2 scope=spfile;