Fernando Nasser wrote:
> Ole Streicher wrote:
>
>>
>> I'd propose to put this information directly into the table - either
>> by removing the two not supported levels, or by flagging them somehow.
>>
>
> As I've mention before they _are_ supported and as _per standard_.
> The standard allows implementations to provide a higher isolation
> level in place of any lower level that is not implemented.
The statement:
SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;
results in an error.
This means, that this particular isolation level is *not* supported.
The "compatibility' section of the 'SET TRANSACTION' charpter in
postgres SQL reference seems to disagree with you too:
"PostgreSQL does not provide the isolation levels READ UNCOMMITTED and
REPEATABLE READ. "
Also, the Appendix "C.2" to the User's Guide - "Unsupported features"
has both REPEATABLE READ (F111-01) and READ UNCOMMITTED (F111-03) listed
as 'unsupported'.
Also, I don't know what standard really says about this ... but I have
never seen a database, that would claim that it supports any isolation
level just because it supports a higher one... To me, such definition of
'support' doesn't, make any sense at all...
Even if you are right, and the standard, indeed, suggests that you only
have to implement 'serializable' to claim support of all four levels...
I don't see much point in agruing that, other than just to say 'postgres
is cool' ;-)
For all practical purposes, the support isn't there, and the
documentation seems to properly (and repeatedly) state that.
Dima
