Psycopg psycopg

Comments and changes to this ticket

• 

  Daniele Varrazzo June 30th, 2011 @ 02:05 PM

  • Tag set to “pool”
  • State changed from “new” to “open”

  I see other problems in the pool too: if a connection is returned to the pool while a transaction is open, the connection is left idle in transaction.

  A robust way to handle all the cases I think would be to check the transaction status, so cases such as lost connection or connection in transaction/error can be handled properly.

• 

  Daniele Varrazzo June 30th, 2011 @ 03:23 PM

  Looking at the pool code, there is a way to discard the connection: use putconn(cnn, close=True), but it is not documented: I will fix the documentation.

  However I think the pool should be more careful on the connection it receives: I will fix it to detect broken/intrans/error connections and deal with them.

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  Sam Morris June 30th, 2011 @ 05:07 PM

  Ah, thanks for that information.

  Does this look like the right thing to do in order to get a connection from the pool? Sorry if this sounds like a support request, but it will be a while until updated versions of psycopg2 filter down to end-users, so some example code might be helpful:

  conn = None
  while conn is None:
      c = pool.getconn()
      try:
          c.cursor().execute('SELECT 0')
      except:
          pool.putconn(c,close=True)
      else:
          c.rollback()
          conn = c
  try:
      f(conn)
  except:
      conn.rollback()
      raise
  finally:
      pool.putconn(conn)
  

• 

  Daniele Varrazzo July 1st, 2011 @ 10:52 AM

  Yes, what you propose is a robust way to get a connection from the pool guarding from a server disconnection. I don't want to add a probe query into the pool code: the code will have a guard on putconn() discarding a broken connection but the f() could still receive a connection we don't know if broken. If your f() can't cope with it, you'd better keep your probing pattern even with future psycopg releases.

• 

  Daniele Varrazzo August 9th, 2011 @ 10:39 AM

  • State changed from “open” to “resolved”

  The pool now is able to watch for the connection returned, caring to rolling back an eventual open connection or to dispose broken ones.