Re: improving async support in psycopg

On 28/03/2010 10:42, Jan Urbański wrote:
> On 28/03/10 04:10, Daniele Varrazzo wrote:
>> On Sun, Mar 28, 2010 at 2:35 AM, Daniele Varrazzo
>> <[email protected]>  wrote:
>> OTOH, looking at the pqpath.c, many functions call PQexec (via
>> pq_execute_command_locked) and set the connection state according to
>> its result (begin, commit and rollback). reset() instead executes a
>> sequence of 2 or 3 operations (something similar to what connect()
>> does). If those methods were to be made async, it seems to me that the
>> knowledge about "how to block" should be available at C level.
> 
> Yeah, there are places where psycopg2 issues queries behind your back :(
> That's why I said that a user of the async features would probably have
> to set the transaction isolation level to autocommit and issue his own
> BEGINs and COMMITs from a Cursor.execute() instead.

I still haven't skimmed over the patches but the more I read the
paragraph above, the more I like it. It is reasonable that the client
code using psycopg in async mode will usually be some asynchronous
framework of some sort and not code written directly by the user. Then
it make sense to depythonize the API a little bit and let the client
code use psycopg as a facility to issue asynchronous queries. Also I
don't think that keeping a single path in the code is such a good idea,
so why not have a connect() call that when invoked with async=True takes
a completely different path and setup everything for async mode? It will
put the connection into autocommit and disable (meaning that they will
raise an exception) methods such as commit(), rollback() and
set_transaction_isolation(). We just need a list of what psycopg should
or should not do.

federico

-- 
Federico Di Gregorio                                       fog-NGVKUo/i/[email protected]
   God is real. Unless declared integer. -- Anonymous FORTRAN programmer

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