Re: find out default transaction isolation level

Some discussions here:

http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&selm=130ba93a.0211100903.20c5d467%40posting.google.com

I am a bit suspicious of your claim that you are reading uncommitted data from different sessions. Are you sure all sessions are still connected when you ran the query? Or was one of the sessions got disconnected and data got committed by default?

ORACLE supports read-committed, serializable and read-only transactions. Read-committed is the default. As I recall, the init param "serializable" could be used to change the default. But this param has been obsoleted since ORACLE 8. Interestingly, you can only use "alter session set isolation_level" to set "Read-committed" and "serializable" transaction. You have to use "set transaction" to set "read only" transaction. You can tell a transaction is in "serializable" isolation level as discussed in the link. I have not found out how to tell if a transaction is read only, by querying a view. Though it is pretty obvious you can not do any delete, update, insert within a read only transaction. It seems "set transaction read only" implicitly licks off a transaction, you can not set it back to "read write" without ending it with a rollback, commit or a DDL. And yet somehow this read only transaction is not recorded in v$transaction.

• Jusung Yang

Michael Howitz <mhowitz_at_firemail.de> wrote in message news:<3DDCCB03.8000100_at_firemail.de>...
> Niall Litchfield wrote:
> > the default level in all versions (including 9.2) is read committed. This
> > can only be changed on a per transaction or per session basis. What problems
> > are you having that you attribute to a difference in isolation level?
>
> so it seems to be the other way round. if i understood 'read committed'
> correctly, it meens that you can only read data which is comitted.
> now i was able to read data which was not yet commited, although i was
> connecting using another connection. bis this might be the problem.
> because i'm using PHP4 to connect my database & it tries to share the
> connections when you do not explicitly say: new connection.
>
> maybe we relied on this feature & now had problems because in one case
> we used new connections to work without autocommmit.
Received on Thu Nov 21 2002 - 13:39:01 CST