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 - 02:26:02 CST
