RE: [HACKERS] READ COMMITTED isolevel is implemented ...

Hello All,

> -----Original Message-----
> From: owner-pgsql-hackers@postgreSQL.org
> [mailto:owner-pgsql-hackers@postgreSQL.org]On Behalf Of Vadim Mikheev
> Sent: Saturday, January 30, 1999 2:55 AM
> To: hackers@postgreSQL.org
> Subject: [HACKERS] READ COMMITTED isolevel is implemented ...
> 
> 
> and this is now the DEFAULT isolevel.
>

It's different from current(v6.4.2).
The way will be provided to upgrade user's current code ?
> I run some tests to ensure how it works, but not so much.
> Unfortunately, currently it's not possible to add
> such tests to regression suit because of they require
> concurrent transactions. We could write simple script to
> run a few psql-s simultaneously and than just put queries
> to them (through pipes) in required order. I have no time
> for this now...
> 
> Processing updates in READ COMMITTED isolevel is much
> complex than in SERIALIZABLE one, because of if transaction T1
> notices that tuple to be updated/deleted/selected_for_update
> is changed by concurrent transaction T2 then T1 has to check
> does new version of tuple satisfy T1 plan qual or not.

How about   UPDATE t set x = x + 1 where .... ?

The values of x used for x = x + 1 are at the time when statement 
started ?
It seems that this case also requires re-execution.

Thanks.

Hiroshi Inoue
Inoue@tpf.co.jp