On 06/29/2016 05:23 PM, Jonathon Nelson wrote:
I noticed some strange behavior with QueuePool when the pool_size is
exactly 1.
(this is with 1.0.13). With an app that basically does this:
e = sa.create_engine(..., pool_size=N)
while True:
with e.begin() as trans:
# perform a simple query
I see this behavior (observed with strace, but turning on connection
logging will do it too):
With pool_size == 1, db connections opened, used, and then closed.
I don't see that (using netstat w/ mysql, I see one TCP connection,
stays open). How are you detecting that db connections are "open"?
Note that the pool also has an "overflow" that will allow it to go over
"pool_size" if more than one connection is requested simultaneously.
Set that to zero to get the pool to stay on exactly one connection.
With pool_size == 2, *two* database connections remain open, neither are
closed.
Something seems weird with pool_size==1. :-(
The logs:
DEBUG:sqlalchemy.pool.QueuePool:Created new connection <connection
object at 0x2d7db10; dsn: 'dbname=zarp', closed: 0>
DEBUG:sqlalchemy.pool.QueuePool:Connection <connection object at
0x2d7db10; dsn: 'dbname=zarp', closed: 0> checked out from pool
DEBUG:sqlalchemy.pool.QueuePool:Connection <connection object at
0x2d7db10; dsn: 'dbname=zarp', closed: 0> being returned to pool
DEBUG:sqlalchemy.pool.QueuePool:Connection <connection object at
0x2d7db10; dsn: 'dbname=zarp', closed: 0> rollback-on-return
DEBUG:sqlalchemy.pool.QueuePool:Connection <connection object at
0x2dbb390; dsn: 'dbname=zarp', closed: 0> being returned to pool
DEBUG:sqlalchemy.pool.QueuePool:Connection <connection object at
0x2dbb390; dsn: 'dbname=zarp', closed: 0> rollback-on-return
DEBUG:sqlalchemy.pool.QueuePool:Closing connection <connection object at
0x2dbb390; dsn: 'dbname=zarp', closed: 0>
DEBUG:sqlalchemy.pool.QueuePool:Connection <connection object at
0x2d7db10; dsn: 'dbname=zarp', closed: 0> checked out from pool
DEBUG:sqlalchemy.pool.QueuePool:Created new connection <connection
object at 0x2dbb390; dsn: 'dbname=zarp', closed: 0>
DEBUG:sqlalchemy.pool.QueuePool:Connection <connection object at
0x2dbb390; dsn: 'dbname=zarp', closed: 0> checked out from pool
DEBUG:sqlalchemy.pool.QueuePool:Connection <connection object at
0x2dbb390; dsn: 'dbname=zarp', closed: 0> being returned to pool
DEBUG:sqlalchemy.pool.QueuePool:Connection <connection object at
0x2dbb390; dsn: 'dbname=zarp', closed: 0> rollback-on-return
DEBUG:sqlalchemy.pool.QueuePool:Connection <connection object at
0x2d7db10; dsn: 'dbname=zarp', closed: 0> being returned to pool
DEBUG:sqlalchemy.pool.QueuePool:Connection <connection object at
0x2d7db10; dsn: 'dbname=zarp', closed: 0> rollback-on-return
DEBUG:sqlalchemy.pool.QueuePool:Closing connection <connection object at
0x2d7db10; dsn: 'dbname=zarp', closed: 0>
DEBUG:sqlalchemy.pool.QueuePool:Connection <connection object at
0x2dbb390; dsn: 'dbname=zarp', closed: 0> checked out from pool
--
Jon Nelson
Dyn / Principal Software Engineer
p. +1 (603) 263-8029
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