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Re: Thinking about archived redo-logs SIZE

From: Howard J. Rogers <hjr_at_dizwell.com>
Date: Tue, 17 Aug 2004 15:15:14 +1000
Message-ID: <41219480$0$18394$afc38c87@news.optusnet.com.au>


"Michel Cadot" <micadot{at}altern{dot}org> wrote:

> 
> "Howard J. Rogers" <hjr_at_dizwell.com> a écrit dans le message de
> news:412171b6$0$11790$afc38c87_at_news.optusnet.com.au...

>> José Arango wrote:
>>
>> > Hello everyone,
>> >
>> > I'm trying to figure out the size of the archived redo-logs. First,
>> > imagine this scenario. My redo logs are of size 10MB (each one of the
>> > three I have). How can I know the percentage occupancy on these redo
>> > logs? After a redo log switch, the DB switches to the other one
>> > (imagine there are no transactions) how can I notice the difference
>> > between this redo log (with no actual transaction) and one that is
>> > about to fill up? ...since by looking at the size I can't never tell.
>> >
>> > Also...when the archiver moves the old redo log..to the archive
>> > destination..does it moves the complete (10MB) file to the archive
>> > destination? Or does it just takes the "actual data within the file" in
>> > order not to waste resources? I'm thinking it would be a waste of time
>> > copying the old redo-log (full 10MB) to the archive destination since
>> > that redo log doesn't have really actual transactions.
>> >
>> > Example: If there'a a 10MB redo log (with 20% usage)..and then occurs a
>> > log switch...will the final archived redo-log be 2MB?
>> >
>> > Of course, I'm assuming the DB has a time interval (let's say 30
>> > minutes) in which the log switch will be performed...
>> >
>> > I don't have a DB with me right now so I can't test.
>> >
>> > Your help will be appreciated.
>> >
>> > Thanks,
>> > Jose
>>
>> ARCn takes an intelligent copy of redo data. It does not do byte-for-byte
>> copies of the online logs as 'copy' or 'cp' would do. Therefore, if you
>> have 2MB actually used in a 10MB log, and you manually force a log
>> switch, the resulting archive will be 2MB in size.
>>
>> There is no log switch interval on the database (unless you create one by
>> scheduling a job to switch logs). Log switches otherwise only happen when
>> one online log fills up, and further redo is generated which needs to be
>> written somewhere.
> 
> 
> ARCHIVE_LAG_TARGET forces a log switch after the time specified.


That is 10g specific, if I'm not much mistaken.

Regards
HJR
>>
>> If you want to know the percentage occupancy of an online redo log, you
>> can delve into SYS.X$KCCCP. The column labelled CPODR_BNO shows you the
>> Current Position Of the Database Redo Block Number. Multiply by (usually)
>> 512 bytes to get the position in more meaningful terms. For example, if
>> it displays 500, it means 256KB of redo has been written into the current
>> log. The number resets at each log switch.
>>
>> Unless you are in the habit of forcing log switches by hand, you can be
>> assured that the two logs of yours which are not the current redo log are
>> 100% full, give or take a little slack space.
>>
>> Regards
>> HJR
>>
>>

> Received on Tue Aug 17 2004 - 00:15:14 CDT

Original text of this message

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