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Thread: What can possibly generate REDO?

  1. #1
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    What can possibly generate REDO?

    I've got a small database (8.1.5.0 on NT4) that I look after that is puzzling me. It has about 15 tables, the largest of which has 500 rows. Over the past month the tables have not grown and there is virtually no 'traffic' that I can see. (Theres also no technical documentation that shows the application and DB details!!).There is a link from another DB to this, but it only reads data.

    But this DB is generating and archiving a 1Mb redo log every 15-20 mins.

    I'm stumped as to where to look to see whats causing this? Is there anything - other than DML - that can fill up redo logfiles?

  2. #2
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    Re: What can possibly generate REDO?

    Some tablespace is forgotten in "BEGIN BACKUP" mode? Just guessing...
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  3. #3
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    Use logminer to figure out what is being written to the archived redo logs.
    Jeff Hunter

  4. #4
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    JMac, just to add : ** EVEN ** a SELECT can (and WILL) generate redo in the case of delayed block cleanout, ok ? And in a small database(with a even smaller blok buffer, probably), more chances yet of this ...
    SO, use the sugested tools , OR (if possible) dump the apropriated v$ stats views some times to find what sessions are doing most of the redo, and then look for the SQLs in that sessions.
    SURELY you will find some "undocumented" job popping, some remote SQL sended by a remote machine, some trigger doing works, things like that. The SUREFIRE thing is : there is NO "phantom" redo in an Oracle bd, IF redo is being generated, SOMEONE is doing something, no doubt about this.

    Regards,

    Chiappa

  5. #5
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    With that small database, it must be somthing "silly". I am still curious if the tablespace(s) are in BEGIN BACKUP mode :-)
    Oracle Certified Master
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  6. #6
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    Originally posted by JChiappa
    JMac, just to add : ** EVEN ** a SELECT can (and WILL) generate redo in the case of delayed block cleanout, ok ? And in a small database(with a even smaller blok buffer, probably), more chances yet of this ...
    To add still more as far as Select's are concerened.. Some complex queries will have a TEMP table transforms.. and intermitent data will be inserted into these tables ( ofcourse under the schema SYS )..

    Abhay.
    funky...

    "I Dont Want To Follow A Path, I would Rather Go Where There Is No Path And Leave A Trail."

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  7. #7
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    With that small database, it must be somthing "silly". I am still curious if the tablespace(s) are in BEGIN BACKUP mode :-)
    Sorry Julian, No there are no TBSs in Backup mode.

    I need to get the developers to tell me what the hell its doing!

  8. #8
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    Originally posted by marist89
    Use logminer to figure out what is being written to the archived redo logs.
    Personally, I'd rather go to the developer and say "WTF is process x from machine y doing during time period a through b. It is generating a load of redo from query z." But hey, I like to look like I know what I'm doing.
    Jeff Hunter

  9. #9
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    Originally posted by JMac
    Sorry Julian, No there are no TBSs in Backup mode.

    I need to get the developers to tell me what the hell its doing!
    Ahrr :-) Take one archivelog and play with it using Logminor.
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  10. #10
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    Yeah, I much prefer to look like I know what I'm talking about when I quiz developers!

    Logminer - is it available with Standard Edition?

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