Re: Transaction control overhauling - Mailing list psycopg

On 12/05/11 00:43, Daniele Varrazzo wrote:
> Hello,
>
> I think psycopg needs some cleanup in the area of the transactions control.
[snip]

Hi Daniele,

I pretty much agree with your analisys, I just have a couple of comments:

> I. don't issue any query at startup and, by default, don't pass any
> isolation level together with BEGIN:
>
> II. add a method conn.set_transaction(isolation_level=None,
> read_only=None, deferrable=None) allowing to change one or more of the
> transaction settings. Calling the method would terminate the current
> transaction and put the new settings in place. Note that there are
> several ways for implementing this:

I'd make this a keyword argument function with the following signature:

conn.set_transaction(
    isolation_level=None,
    autocommit=None,
    deferrable=None,
    readonly=None)

to keep everything related to transaction management in a single
function. I don't like the proposed autocommit() method because it is
yet another DBAPI extension and must keep that to a minimum. Also, I
sorted the parameters in set_transaction() from the probably most used
to least.

> II. 1. store variables in the connection object and pass the relative
> SET TRANSACTION at the following BEGIN
>
> II. 2. run a query SET SESSION CHARACTERISTICS AS ... and not store
> anything in the connection status
>
> II. 3. run a query to set the GUC instead (SET default_whatever AS
> value): very similar to II. 2., but it also allows passing the value
> "default", meaning "reset to the configuration value", an option
> apparently missing with the SET SESSION CHARACTERISTICS syntax.

Do we need the ability to pass "default"? When the user call
set_transaction() with missing or None parameters do we want to send
"default" or stay with the current value? I favor the latter, e.g.,

conn.set_transaction(isolation_level=XXX, deferrable=YYY)

should not reset the autocommit or readonly values to default.

> III. add an independent method conn.autocommit(value=True). A less
> verbose method for a frequently used functionality.

Nope, see above.

> IV. for backwards compatibility, convert isolation_level into a
> property, querying the server to know the current status.

Yesss.

>
> V. keep set_isolation_level() for backwards compatibility, converting
> it into a wrapper for the other methods.

Yesss.

federico

--
Federico Di Gregorio                         federico.digregorio@dndg.it
Studio Associato Di Nunzio e Di Gregorio                  http://dndg.it
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