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Home -> Community -> Usenet -> c.d.o.server -> Re: A Theoretical Situation
On Fri, 01 Aug 1997 16:47:03 -0500, Scott Thompson <sft_at_lucent.com> wrote:
>Oracle will not 'wrap' onto an 'active', one containing open
>transactions,
>redo log in archivelog mode.
>
Actually, it will.
Oracle will not wrap onto a redo log file containing REDO for blocks that have not yet been checkpointed. Once these changed blocks are checkpointed, the redo log file is available for reuse regardless of the state of the transactions that generated the redo. Oracle will also checkpoint (flush to disk) dirty blocks that contain uncommitted changes. These require UNDO which is stored in the rollback segment (and rollback is checkpointed as well so the undo needed is safely on disk).
You can have 100k of online redo log in 2 50k files. You can have one transaction that changes 1meg of data (in archive or no-archive log mode). It will succeed and it will wrap logs many many times..
The difference in wrapping with archive and no-archive log mode is that in archive log mode we also will not wrap on a redo log file until it has been successfully copied elsewhere. In no-archive log mode, we don't have any such concerns and will wrap as soon as the checkpoing is complete.
>--
>Scott Thompson
>
>Alan Gano wrote:
>
>> Hi,
>>
>> Assuming an instance of this configuration:
>> - 5 redo logs of 10K each.
>>
>> Assume this situation:
>> - A single transaction (say an UPDATE) produces more than 50K of redo
>> information, filling the redo logs, and then wraps around.
>> - There is plenty of rollback space for the transaction.
>> - The transaction is not committed.
>>
>> In this situation, some redo information concerning the transaction is
>>
>> being overwritten or written off to offline archive logs. I would
>> assume
>> that at least some of the modified blocks for this
>> offlined/overwritten
Thomas Kyte
tkyte_at_us.oracle.com
Oracle Government
Bethesda MD
http://govt.us.oracle.com/ -- downloadable utilities
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