[DB-SIG] Optional DB API Extensions
Thu, 25 Oct 2001 16:21:16 +0200
At 13:11 2001-10-25 +0200, Federico Di Gregorio wrote:
>i am working on this for psycopg. it is somewhat simplier that your
>proposal, just a way to ask the db for a given isolation level. or are
>isolation levels defined at the SQL standard level?
They are, but how many RDBMS's adhere to the standard?
SQL/92 defines these transaction levels:
READ UNCOMMITTED, READ COMMITTED, REPEATABLE READ and SERIALIZABLE.
I'm not sure all major databases still implement them quite like that
though. If I remember correctly, DB2 used other names last time
I tried (v 5.2?). Oracle 7 used 3 options for SET TRANSACTION: READ
ONLY, READ WRITE and USE ROLEBACK SEGMENT ... But that's not really
isolation levels. I don't know about more current Oracle versions.
SQL Server 7.0 follows the standard. So does MySQL, which is a bit
funny since it doesn't handle transactions at all in the standard
version. :-) PostgreSQL only supports READ COMMITTED and SERIALIZABLE,
but the manuals warn that SERIALIZABLE isn't quite what it says...
Magnus Lyckå, Thinkware AB
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