Re: Reading data from oracle database

From: Mladen Gogala <>
Date: Fri, 12 Dec 2008 10:55:56 +0000 (UTC)
Message-ID: <ghtfvs$qk8$>

On Fri, 12 Dec 2008 00:23:54 -0800, oracle user wrote:

> Can anyone help me on understanding how data is read from oracle
> database.There is a db writer process which writes data in the dbf files
> from dirty buffers. Similary what is the the mechanism for reading data
> from dbf files of oracle database.
> If a user connect's to sqlplus session and gives the command 'select
> * from table x' ,what all process happens next. Thanks in Advance

Many things can happen, depending on the version of database. Short story goes like this:

  • User connects to the database. User session structures are allocated in SGA.
  • User submits SQL statement and is given a server process to service his request. Server process does its own reading but writing is delegated to the database writer(s). The allocation process is complex as the allocated server can be shared, pooled or dedicated.
  • The server process executes the request and returns the result to the user. How is that done also depends on the allocated server.

All of this is described in the literature. In my opinion, the best book about Oracle architecture is "Expert Oracle Database Architecture" by Tom Kyte. You can also try with "Practical Oracle8i: Building Efficient Databases" by Jonathan Lewis. The latter book is a bit old but still relevant.

Mladen Gogala
Received on Fri Dec 12 2008 - 04:55:56 CST

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