Re: log manager in ORACLE?

Thank you Howard!

"Howard J. Rogers" wrote:

> I'll just say that I have no problem with someone asking these sorts of
> questions. They are not that obvious from the supplied documentation, which
> can sometimes be utterly Byzantine, and a "nuisance" asking sensible
> questions is a good opportunity to re-state that which we *take* to be
> obvious, but which sometimes needs restating in blindingly obvious terms.
> The restatement can be helpful to others.
>
> HJR
>
> "Sybrand Bakker" <postbus_at_sybrandb.demon.nl> wrote in message
> news:a20d28ee.0202130018.256f1979_at_posting.google.com...
> > Y <newdbms_at_yahoo.com> wrote in message
> news:<3C69D7EB.7A2B650C_at_yahoo.com>...
> > > 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
> > > > >
> >
> >
> > 1 rollback is fetched from the rollback segment which can be either in
> > memory, or on disk. Oracle tries to postpone writing to disk as much
> > as possible and clients don't write to disk, this is handled by the
> > database writer aka DBWR
> >
> > 3
> > The limits are hardcoded can not be changed and have no relationship
> > with the checkpoint interval. The log_buffer itself is adjustable in
> > size, the thresholds aren't
> >
> > I know for a fact even Oracle Support recommends their customers to
> > RTM.
> > Please try to do so, or you will become a nuisance to this group, and
> > nuisancees are usually ignored.
> >
> > Regards
> >
> > Sybrand Bakker,
> > Senior Oracle DBA
Received on Wed Feb 13 2002 - 07:54:53 CST