Re: Redo logs and rollback segments difference ?

The redo log contains before and after images. As for the rollback segment, it depends, if it is a pure insert on the table, it will contain the rowid of the rows that are being inserted without commit; if it is a delete on the table, it will contain all the information of the deleted rows.
if it is a update, it will contain the before and after images of the columns that are being updated.

Winnie

johnvue_at_gte.net wrote in message <6qho0l$gfe$1_at_news-1.news.gte.net>...
>Just for your info, more than one book states that rollback data first
>has to go through redo buffer which of course goes through the redo
>logs. So the redo logs contain BOTH before and after images. You are
>correct in saying Oracle doesn't USE the redo logs for rolling back.
>
>On Sat, 08 Aug 1998 11:40:58 +0200, in comp.databases.oracle.server
>you wrote:
>
>>Rollback data contains the before image, the data before any changes, redo
>>log contains the after image, the changed data. Henc, In recovery the redo
>>log is used for roll forward and the rollback segments (which are also
>>protected by redo log, any change is logged there) for rollback. In fact,
>>writing the update,insert,delete changed data to the redo log is the first
>>what is being done. Oracle assumes there are hotspots in the database, who
>>are changed by more than one process. Transactions are piggybacked, until
>>(usually 8) blocks in the cache are dirty. If you have 8 dirty blocks they
>>are being written to the database files. This can be done because the
>>changes have already been written to the redo log file.
>>Hth
>>Sybrand Bakker
>>(postbus_at_sybrandb.demon.nl)
>>
>>Jean-Francois Vincent wrote:
>>
>>> Hello, i wonder what is the conceptual difference beetween redo log and
>>> rollback segments under ORACLE. It seems the both contains transactions
>>> bring possibility to rollback transaction, i guess transaction are
>>> written twice in rollback and in redo log. Am i right ?
>>> Can you explain me in detail the difference of each one ?
>>> thank you very much.
>>>
>>> J-Fr.
>>
>>
>
Received on Sat Aug 08 1998 - 10:59:07 CDT