Re: log manager in ORACLE?

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"Y" <newdbms_at_yahoo.com> wrote in message news:3C6881C6.45770644_at_yahoo.com...
> Hi,
> I am using Oracle 8i EE.
> I took a quick view of oracle books. I haven't found a direct answer for
> my questions.
> I just want to know how log manager works in Oracle?
>
> For example, when I issue one update sql request,
>
> 1. Oracle read the datablock from datafiles on disk into buffer. Before
> update data block, oracle first write the before and after image to log
> buffer?
>

the before image is written to the rollback segment. Changing the rollback segment implies changing a data block: the change is copied to the log_buffer
Update implies changing a data block, the change is copied to the log_buffer

> 2. When and what information will be written to Rollback Segments?

See above
>
> 3. When the transaction end or the log buffer pool full, log buffer
> pool flush to redo log files?
>

The log_buffer will be flushed to disk
either
1 every 3 secs
2 when it is one third full
3 when 1M of the log_buffer is dirty
4 when a transaction is committed.
> 4. The rollback segments will only keep before and after image for open
> transactions. Is that correct?

NO. The after image is NOT in the rollback segment.

The redo log files will store the before
> and after image of unactive transactions. Is that correct?
>

NO the redolog files store the before and after image for ALL transactions, whether active or unactive. This allows for 'playing back' all mutations after a crash (of course you must have archived those redo log files)

Please read the Oracle Concepts Manual.

--
Sybrand Bakker
Senior Oracle DBA

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> Thanks for any help?

> Y

>