What is the measure for tablespace IO writes efficiency?
We've started transferring in the last days our storage from DMX3 to Vmax.
I want to compare performance of specific tablespace before and after the transferring.
In AWR ,in the section of Tablespace IO stats I checked the measure "Av Rd(ms)" regarding reads.
Is there a measure for writes?
How can I know that I've got an improvements regarding writes?
Thanks in advance,
How about "Av Buf Wt(ms)"?
Also maybe you want the Average ms it take to read one block which is:
Av ms/blk = Av Rd(ms) / Av Blks/Rd
"The person who says it cannot be done should not interrupt the person doing it." --Chinese Proverb
Av Buf Wt(ms) is a threshold value for measuring Buffer Busy Waits.
It's not related necessarily to writes watings.
Provided timed_statistics is set to TRUE v$filestat shows the information you are looking for.
Having said that, please take into consideration that Write I/O performance is a tricky matter in the sense that:
1- Writes to datafiles are done by DBWR in the background so as long as DBWR can keep up with the load you really don't care about I/O performance;; DBWR will get it done and user community will never notice performance fluctuations.
2- Writes to logs and temporary segments on the other hand are done in the foreground therefore poor performance in such segments will immediately have a negative impact on overall performance.
Bottom line, don't waste your time analyzing Write I/O on standard "data and indexes" data files; focus your attention on Logs or Temporary segment data files.
Last but not least, when looking at Write I/O I would suggest to check what's the performance your I/O subsystem is giving you - talk to your storage guy and ask her/him to report 'service levels" to you. Also ask for the technical specs of your particular I/O subsystem so to compare what the vendor sold against actual service levels.
Hope this helps.
Pablo (Paul) Berzukov
Author of Understanding Database Administration
available at amazon and other bookstores.
Disclaimer: Advice is provided to the best of my knowledge but no implicit or explicit warranties are provided. Since the advisor explicitly encourages testing any and all suggestions on a test non-production environment advisor should not held liable or responsible for any actions taken based on the given advice.
Thanks a lot Pablo!
You were very helpful
Which release of Oracle are you using? You can gather IO stats (via dbconsole/gc is one way, one-click button to have Oracle collect that info).
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