Re: New bie Information of redo and datafile

From: nilesh kumar <>
Date: Sat, 5 Apr 2008 01:31:43 +0530
Message-ID: <>

Thank you very much Dennis,

You have answered both my second question very clearly and in simple words.

Thank you
Happy weekend


On Fri, Apr 4, 2008 at 11:01 PM, Dennis Williams <> wrote:

> Nilesh,
> Since I don't see where anyone replied to your questions, I'll take a
> crack at it.
> 1. I'm not sure what question you are really trying to ask. At a high
> level, Oracle writes enough information to the redo log that it can repeat
> the change if needed for recovery purposes. If you really want to know more
> specifics, learn the LogMiner, since a lot of the redo log information is
> made visible with this tool.
> Oracle doesn't directly write to a data file. It first writes to a data
> block in memory. If this is an update operation and the block isn't already
> in memory, Oracle will have to retrieve it from disk first. If it is an
> insert, Oracle will check the free list first and create a new block if the
> free list is empty. Many people have the misconception that Oracle
> immediately writes the data block back to disk. Since you didn't ask that
> question, I'll leave it for your further study :-)
> 2. In Oracle, a tablespace may have more than one data file. So you
> measure the free space at the tablespace level, not the data file level.
> When you create a datafile, you specify the tablespace that datafile is
> assigned to. Oracle measures free space in the DBA_FREE_SPACE view, which
> lists free space by tablespace. As a test, add a data file, checking the
> free space before and after and you'll see an immediate increase.
> I hope this addresses your questions.
> Consider reading the Oracle Concepts Manual, which addresses most of these
> concepts. It isn't large, and is clearly written, easy to understand, and
> best of all FREE!
> Dennis Williams
> On 4/3/08, nilesh kumar <> wrote:
> >
> > Hello All,
> >
> > Good Morning!,
> > Hope every one is doing good.
> >
> > I have a very simple two questions:-
> >
> > 1. If I issue a sql statement to insert value or delete value or modify
> > the value in the table. What exact information goes in the redolog file and
> > datafile. I know that redo entries goes in the redolog file, but I need to
> > know what exactly get stored in the redolog file and datafile.
> >
> > 2. Suppose a dba gets a pager that datafile threshold has reached 90%
> > and he goes and add a datafile . How does oracle comes to know that after
> > the current datafile is full it needs to store the data in the new datafile
> > added.
> >
> > Thanks
> > Nilesh
> >
> >
> >
> >

Temples & Softwares are more or less the same, first we build them and then
we pray ;)

Received on Fri Apr 04 2008 - 15:01:43 CDT

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