Re: Oracle 7 Data File Storage - Newbie Question

Hi Bernadette -
For a more complete ( and probably more technically correct ) explanation of Oracle's 'mechanics' try the Server Concepts manual or any good book on RDBMS storage structures....

The database is a collection of objects ( tables,views,indexexs,procedures,packages, etc ) that are accessed to retrieve 'stuff' stored in the tables....

The actual contents are stored in one or more tablespaces compised of one or ,more typically, many data files ( these are actual, operating system files just like other files stored on a filke server ) ....

When a user requests a particular record or group of records an image of the data is copied into a buffer awaiting some request - ( i.e. update, delete, select ) - each user ( should several request the same record at the same time ) will get an image of the data as it was stored at the time of the request --- at this point no user is accessing the actual, stored data ( the data on disk ) -

The Oracle RDBMS engine handles the access,change,and storage by processes that run in the background of each instance and these serve to protect the integrity of the data - Read about this is the manuals - particularly about the guaranteed 'read-consistancy' of the data

There is no way to fully explain the workings of a large, sophisticated RDBMS like Oracle in a posting, so read as much as you can find about its structures, methods and features......All of the above is greatly simplified and more 'metaphor' than actual, technical info, but it should give you an idea about what's goin' on.....

As to question 3 - there is no 'snapshot' of the database sent to the PC - Oracle is true client/server - the PC acts a requestor for the database processes to reply to....

Hope it isn't to confusing - I probably shouldn't try this on a Friday....

John Greco
Oracle DBA
Email to john.greco_at_dot.state.mn.us

Bernadette Pinto <b.pinto_at_zetnet.co.uk> wrote:

>In a multi-user environment where, say, three users are accessing the
>same database tables, where is the data file(s) on which the data is stored?
>
>Also, if each user asks for the rowid of a row from one specific
>table, will each user get the same rowid returned? (I mean, will the
>rowid for the user's database instance or the server's database be returned).
>
>
>The two questions above lead me to asking this third question:
>
>How is an Oracle database stored? I have assumed that in a multi-user
>environment the database was stored on the server. I also assumed
>that each client PC had an 'instance' of the database (I.e., a
>snapshot of the server's database stored locally). If this is so, is
>it possible to return information regarding the physical location of
>the local database instance (can't think why you would want to, but
>am curious).
>
>Thanks for taking the time to answer these questions.
>
>Best wishes
>
>Bernadette
>
Received on Fri Jul 24 1998 - 09:56:08 CDT