Online Redo logs

[Sonia]

Hi,
Whenever any changes has to be written to Online Redo log files, that has to be done in the memory; where does that happen. Does it happen somewhere in OS buffers

Regards

[ggnanaraj]

redo log buffer in SGA. LGWR writes from redo log buffer to redo log file.

The following could be useful...

http://otn.oracle.com/docs/products/...inere.htm#3848


HTH.

[Sonia]

Do u mean to say it reads the blocks and puts in log buffer and does the modification.......and again writes them back to disk......?

[ggnanaraj]

Hi, you seem to be mixing it up with the database buffer cache(db_block_buffer) in the SGA. The needed database blocks are in this database buffer cache. Whereas, the redo log buffer has the changes made to this database blocks in the database buffer cache.

Check this out...

http://otn.oracle.com/docs/products/...intro.htm#7179

Hope this clears it out.

[Sonia]

Hello....hth,
What i am telling is, any data that has to be wrtten to the file it has to be done in the memory...right...forget abt oracle......any software for that matter............
So for datafiles we have buffer cache....

in the same way, for writing into online redo logfiles it has to be done in the memory...right....so where in the memory.....

[ggnanaraj]

Originally posted by Sonia
in the same way, for writing into online redo logfiles it has to be done in the memory...right....so where in the memory.....

REDO LOG BUFFER IN THE MEMORY.

Cheers.

P.S.: It would do you good if you could read throu' the links I posted. In the 2nd link, there is a very good pictorial representation of what we are discussing.

[Sonia]

who will read the blocks from Redolog file to the redo log buffer ?

[Calvin_Qiu]

As Oracle 9i Administrator Guide said, Redo file are filled with redo records, each of which is a description of a change made to a single block in the database. How does Logminer reconstruct the DML statement in SQL_REDO?

[ales]

Originally posted by Sonia
who will read the blocks from Redolog file to the redo log buffer ?

Nobody. Why should anybody do that?

[Calvin_Qiu]

Originally posted by Calvin_Qiu
How does Logminer reconstruct the DML statement in SQL_REDO?

Done, it will reconstructe one statement for every record changed.