HI，i got a multi-threading program which all threads will operate on oracle DB. So, can sqlalchemy support parallel operation on oracle?
tks!
+1
A:
As long as each concurrent thread has it's own session you should be fine. Trying to use one shared session is where you'll get into trouble.
Branden Hall
2009-07-13 03:29:59
tks，since oracle official document said that you should enable something(don`t know what "something" is yet...) for oracle to use parallel ability..What should i do in sqlalchemy?
Andy
2009-07-13 05:06:15
+2
A:
OCI (oracle client interface) has a parameter OCI_THREADED which has the effect of connections being mutexed, such that concurrent access via multiple threads is safe. This is likely the setting the document you saw was referring to.
cx_oracle, which is essentially a Python->OCI bridge, provides access to this setting in its connection function using the keyword argument "threaded", described at http://cx-oracle.sourceforge.net/html/module.html#cx_Oracle.connect . The docs state that it is False by default due to its resulting in a "10-15% performance penalty", though no source is given for this information (and performance stats should always be viewed suspiciously as a rule).
As far as SQLAlchemy, the cx_oracle dialect provided with SQLAlchemy sets this value to True by default, with the option to set it back to False when setting up the engine via create_engine() - so at that level there's no issue.
But beyond that, SQLAlchemy's recommended usage patterns (i.e. one Session per thread, keeping connections local to a pool where they are checked out by a function as needed) prevent concurrent access to a connection in any case. So you can likely turn off the "threaded" setting on create_engine() and enjoy the possibly-tangible performance increases provided regular usage patterns are followed.
zzzeek
2009-07-24 03:09:36