RE: [HACKERS] MVCC works in serialized mode!

> -----Original Message-----
> From: owner-pgsql-hackers@postgreSQL.org
> [mailto:owner-pgsql-hackers@postgreSQL.org]On Behalf Of Zeugswetter
> Andreas IZ5
> Sent: Monday, December 28, 1998 6:30 PM
> To: hackers@postgreSQL.org
> Cc: 'vadim@krs.ru'
> Subject: Re: [HACKERS] MVCC works in serialized mode!
> 
> 
>     >>    Shouldn't we change default transaction mode now?
>     >>    And use option/SET TRANSACTION MODE to switch to
>     >>    un-chained mode if one like it?
>     >
>     >No comments on this?
>     >I would like to make BEGIN implicit...
>     >Objections?
> 
>     Yes, I object. I think the default behavior should be the one that 
>     is sufficient in most cases. 
>

I have a question about new default(isolation level / transaction mode).

How do we upgrade existent programs,if default is different 
from current ?
I think the isolation level of current PostgreSQL is SERIALIZABLE 
and the transaction mode is un-chained..

As to the isolation level,even SERIALIZABLE isolaton level can't guarantee 
the integrity of current level.
So we must change existent programs anyway ?

Thanks.

Hiroshi Inoue
Inoue@tpf.co.jp
>     As to the isolation level: 
>     Informix and DB/2 default to read committed mode. In most cases this
> is 
>     sufficient.
>     Therefore most clients don't need the extra set transaction
> isolation statement.
> 
>     As to transaction blocks: 
>     Actually most clients never use commit work, and remember
>     that postgresql will never free it's memory before commit. This will
> hog up 
>     memory for otherwise lightweight clients.
> 
>     I also think that the begin work; commit work; statement block is
>     somewhat part of the postgresql philosophy. We do not stand alone
>     with this approach (Informix).
>     Actually the other DB's start the transaction with the first
> modifying 
>     statement, in my opinion a rather weird approach. 
>     I have seen programs that do a dummy update, just to simulate a 
>     begin work, what a waste.
>     But this alone will not work, because a select statement, that needs
> 
>     a sort would have started the transaction earlier (Since it created
> an implicit
>     temp table).
>     I could go on, but you see I don't really like this ...... 
> 
>     If you want to change the behavior, I think we will need a
> changeable default 
>     at database level.
> 
>     Andreas
> 
> 
> 
> 
>