Re: How does Oracle know where to read from

From: amonte <ax.mount_at_gmail.com>
Date: Sat, 11 Apr 2009 00:37:20 +0200
Message-ID: <85c1fb130904101537u67c593f5qc30d87c9cd3868d1_at_mail.gmail.com>

I make a pardon I think I missed the point that accessing dictionary cache does not mean more buffer gets.

Clear now Thanks!

2009/4/10 K Gopalakrishnan <kaygopal_at_gmail.com>

> Alex, Let me try to answer in simple way.
>
> When you run a query, data dictionary provides the file#,block# or
> extent info for that table. Once you know the file#,blok# you can
> compute the dba and search the buffer cache for that dba (yet another
> simple hash function). If not found send an I/O request on that
> file#,block#.
>
> Is this what you are looking for or something else/?
>
>
> On Fri, Apr 10, 2009 at 3:51 PM, amonte <ax.mount_at_gmail.com> wrote:
> > Hi all
> >
> > I have a probably very basic question but I cant think how Oracle does
> it.
> >
> > When we query a table we know that data block address is hashed to
> > read if buffer chain if reading from cache, otherwise look the rows in
> > the data block address.
> >
> > My question is when we run a query how is the data block address
> > obtained? From where?
> >
> > Alex
> > --
> > http://www.freelists.org/webpage/oracle-l
> >
> >
> >
>

--
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Received on Fri Apr 10 2009 - 17:37:20 CDT