What is the measure for tablespace IO writes efficiency?
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  1. #1
    Join Date
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    What is the measure for tablespace IO writes efficiency?

    Hi guys,

    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,
    Nir

  2. #2
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    Cool

    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

  3. #3
    Join Date
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    Hi,

    Thanks!
    Av Buf Wt(ms) is a threshold value for measuring Buffer Busy Waits.
    It's not related necessarily to writes watings.

  4. #4
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    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.

  5. #5
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    Thanks a lot Pablo!
    You were very helpful

    Best regards,
    Nir

  6. #6
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    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).

  7. #7
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    Thanks stecal

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