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Thread: redo log size

  1. #1
    Join Date
    Jan 2006
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    Germany
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    Question Unanswered: redo log size

    Hey
    What is the optimal redo log file size?
    Is there a formula to calculate it based on (insert) transactions?
    (we have 140 inserts (each 200Byte) per second)

    How many Groups (3 or 4 or x)?

    Thanks

    Jochen

  2. #2
    Join Date
    Aug 2003
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    Where the Surf Meets the Turf @Del Mar, CA
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    Provided Answers: 1
    > What is the optimal redo log file size?
    Large enough
    >Is there a formula to calculate it based on (insert) transactions?
    No.
    >How many Groups (3 or 4 or x)?
    Yes.

    About how often do you want the redo log files to switch?
    Then make them that size.
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  3. #3
    Join Date
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    The main requirement for redo logs is that they shouldn't switch more often then about once per hour. If they are switching under normal load quicker then that, increase the size. If they are not then they are OK. An hour is what I have always used. Other users will have different intervals.

    3 is the minimum number of redo logs and should be OK for most installations. If you are not running in archive mode (A VERY bad idea on a production system), then you might want to make the redo logs larger so that you have a higher chance of recovering if your server crashes. The main thing about redo logs in setting up redo-groups. This allows you to have duplicates of the redo logs on different physical drives. If you lose a datafile, you can recover if you are in archive log mode. If you lose your redo logs, you can only do do a point-in-time (PIT) recovery.
    Bill
    You do not need a parachute to skydive. You only need a parachute to skydive twice.

  4. #4
    Join Date
    Jan 2006
    Location
    Germany
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    9

    log mode

    The database is in archive log mode.
    With 50MB redo logfile size the switch is about 7 min.

    beilstwh: What is your commendation for the size? (500MB enough?)

    Thanks

    Jochen

  5. #5
    Join Date
    May 2004
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    Dominican Republic
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    Ferex, use the math: 50 / 7 is around 7.14mb per minute. So, 7.14 * 60 is around 430mb.

  6. #6
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    Jan 2006
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    Germany
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    JMartinez so i calculated the 500MB (size + resort).

    Is it useful to have 2 files in a redo group on SAN?
    The Storage is Hardware RAID1

  7. #7
    Join Date
    Jun 2004
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    Only if your san is broken up into different physical disk groups. Typically SANS use raid or mirrors to protect against a failed drive. You should be OK in that case, however at our site we have 10 redo log groups. Each group contains 2 members of 2 gig each on different physical drives groupings in the SANS.
    Bill
    You do not need a parachute to skydive. You only need a parachute to skydive twice.

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