Tuning Pysical IO

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Tuning Pysical IO

  1. 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$datafile t2 where t1.file#=t2.file#
  2. 2. AnarGodjaev http://anargodjaev.wordpress.com/ order by phyrdsdesc, phywrtsdesc; --- temporary statistics -select t2.name, t1.phyrds, t1.phywrts, t1.readtim, t1.writetim from v$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;

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