PK wrote:
> Hi,
>
> As you know Informix offers 'set isolation to dirty read' - a facility
> to read dirty buffers. I believe DB2 UDB too offers it but not Oracle.
>
> What is the neccessity or justification for an RDBMS to offer such a
> feature and do applications really need it ? I was told by an Oracle
> guy that Informix and DB2 are 'forced' to offer this because of their
> architecture and this is not a 'feature' as such ! He says Oracle can
> offer it in a 'jiffy' by pointing to its undo tablespace (where before
> images of a buffer are kept before modifications) but they will not as
> this is not justified !
>
> I myself (worked with Informix for 9 yrs but now into Oracle for past
> 1 yr ) feel its quite cool. However I would like to get expert
> technical opinion. I don't intend to start a flame at all !
>
> Many thanks
> Prashant
When all you have is a hammer everything looks like a nail....
Here is my take:
Dirty read shows data that potentially gets rolled back and hence there
is a potential to mess up data integrity in case of rollback.
Read consistency shows data that may be stale and hence there us a
potential to mess up data integrity in case of commit.

Both have their uses, both have their faults.

For transaction processing there is only one isolation level that is
correct: Repeatable Read/Serializable. Anything else has various degrees
of buyer beware.

Sidenote: SEQUENCE is "dirty read" by definition and it is quite popular
in Oracle :-)

Cheers
Serge