Re: log manager in ORACLE?

From: Y <newdbms_at_yahoo.com>
Date: Wed, 13 Feb 2002 03:04:31 GMT
Message-ID: <3C69D7EB.7A2B650C@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
> >
Received on Tue Feb 12 2002 - 21:04:31 CST