Redo Log Files - more than 12 per hour

Hello @all,
I have a problem with my redo log files. I get more than 12 switches per Hour. I have 3 Files with 5oM size. I increased the sitz to 15o M, but
I still have 12 switches per hour.
Do anyone know, what I did wrong?
Database:
Oracle 9i
Thanks
Martin

user9528362 wrote:
Hello @all,
yes I know, that 3 switches per hour are perfekt, but I had increased the Size from 5o M to 15oM already and the amount from switches, are not reduced.
So there must be something else, that causes the log switches.Martin,
As I said somewhere above too, 150meg is a tiny size if you are managing a production db. I have already mentioned that make your log file size to at least 500meg and than check. As for the high redo activity, only you can confirm that whether this has been started from now only or was happening before too? In anycase, for an active oltp, 500 to 1gb of redo log file size should be okay.
For the extra redo generation, you have been given link for mining log files using logminer. Try using it to see what is causing extra redo.
HTH
Aman....

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    Now, can this undo data/before image not be stored in the redo log buffer and online redolog files?
    can redo-log files not store this information?
    in fact, is it that when undo tablespaces exist in a database, the undo data/before image is stored in both the undo tablespace and also the redo log files?
    kindly clarify my doubt.
    thank you.

    This question has been asked many times before. The answer is always the same.
    Yes, redo contains the before image of data (and the after-image). Therefore, it **COULD** be used to roll back a transaction.
    BUT... Redo is written sequentially. Using it to rollback your transaction would involve reading through all the redo written by maybe thousands of other people. It would be painfully slow.
    Your transaction is, however, directly linked to just the UNDO that it generates (which is JUST the before image of the data). So, your undo is your undo and doesn't share space with anyone else's undo. Therefore, using it to roll back YOUR transaction is fast.
    The fact that undo is only the before image of the data also makes it faster than wading through a sea of before and AFTER images as you'd find in redo. About twice as fast, in fact, since there's half the data. Roughly.
    Redo also gets written and flushed to disk whenever there's a commit, 3 seconds are up or too much (1MB, actually) redo gets generated between flushes caused by other factors. Your redo gets flushed when those things happen, even if you haven't actually committed your transaction. And redo logs recycle themselves, meaning that your redo -even if your transaction hasn't been committed yet- can be over-written by later transactions. Try rolling back when that's happened, if redo was the source of your rollback data!
    Undo, however, cannot be over-written if the transaction has not been committed. Ever. If you don't commit for three years, there will be three years' undo stored in your database (assuming you had the space, of course!).
    I could go on, but that will do. Redo is there fore RECOVERY, after catastrophe. Undo is there for read-consistency (and the occasional change of mind). Two different functions. Two different mechanisms. Each one highly tuned to doing what it does, why it does it, most efficiently and effectively.

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