Re: How does Oracle know where to read from
- From: K Gopalakrishnan <kaygopal@xxxxxxxxx>
- To: ax.mount@xxxxxxxxx
- Date: Fri, 10 Apr 2009 16:04:34 -0500
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@xxxxxxxxx> 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
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>
>
>
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