Re: log manager in ORACLE?

Y, I think that you would be better served by reading the Oracle documentation. It'll make things a lot clearer for you, and a lot less painful on the members of this board.

;-)

Bricklen

Y wrote:
>
> Hi, Sybrand,
> Thank you so much!
> I wrote some further questions below.
>
> Sybrand Bakker wrote:
>
> > Comments embedded
> > "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
> >
>
> So if I issue commit for the transaction, those changed information will flush
> to datafile later; and if I issue rollback transaction, oracle engine will copy
> the before-image from rollback segment to datafile.
>
> >
> > > 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.
>
> ==========
> All the number here, like 3s, 1/3 full, 1m are hard limit, they are not allowed
> to configured? What's the relationship with the checkpoint interval?
>
> >
> > > 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)
>
> It looks like Redo log like Informix's logical log and Rollback Segment like
> Informix's physical log!
>
> >
> >
> > Please read the Oracle Concepts Manual.
> >
> > --
> > Sybrand Bakker
> > Senior Oracle DBA
> >
> > to reply remove '-verwijderdit' from my e-mail address
> >
> > > Thanks for any help?
> > > Y
> > >
Received on Tue Feb 12 2002 - 21:12:14 CST