On 19 Feb 2001, at 13:27, Stig S. Bakken wrote:
> [email protected] wrote:
> >
> > Hmm, maybe I'm straying too far...I'm not too content of my own
> > suggestions. Your turn...
>
> I've implemented your suggestion now and added a transaction test for
> pgsql as well. Could you give it a shot and see if it solves your
> problem?
>
Funny to see that you've liked my suggestions more than myself :-)
I'll sure do it this afternoon, after "regular" work time :-)...
> One thing I noticed is that postgres shows the changes done inside a
> transaction to other transactions before it is committed. With other
> databases the changes are not visible until you do a commit. This one
> is a bit hard to emulate though.
>
This has to do with the particular level of isolation the DB
implements. PGsql works at 2 possible isolation levels: read
committed, and serializable isolation (you can switch any time with
a SET command). The first mode, that's the default one (and very
few users change it IMHO) allows unrepeatable reads, that is, in
short: querys inside a transaction can read uncommitted data from
other transactions. In the second mode, this is not possible
(updates are not shown to other transactions until committed).
I do not see why you could wish to "emulate" this, however; I think
it's wiser to let each backend handle transaction its own way. I
would leave to the programmer the task to decide if he needs read
committed or serializable isolation level.
If you wish to achieve the maximum compatibility between various
backends, guess the smarter thing it's relying on SQL92
standards. They consider, indeed, the serializable level as the
default. Since it's switchable at runtime, PG could be made to run
at that level "by default" under PEAR simply by issuing the "SET
LEVEL..." in the constructor; in this case, for the user that wish to
use the "relaxed" level, there is still the possibility to switch back
using the reversed command. We'd just to be sure that PG users
migrating to PEAR are aware of this "reversed default", writing it at
capital letters in every piece of doc we can (not that there are
much, but... :-)), or they could be a little confused!
I'll continue later...
bye!
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Fabrizio Ermini Alternate E-mail:
C.so Umberto, 7 [email protected]
loc. Meleto Valdarno Mail on GSM: (keep it short!)
52020 Cavriglia (AR) [email protected]
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