sqlalchemy list connections inside connection pool

[Oğuzhan Kaya]

I made a connection with sqlalchemy to mssql and I used queue pool. I am trying to understand this connetion pool is worked or not. and also I want to see the connections and the queue inside connection pool how can I see?

engine = sal.create_engine('IP',pool_size=1,max_overflow=0)

result = engine.execute('select * from mytable')

result.close()

[Mike Bayer]

engine.pool has some metrics on it:

>>> from sqlalchemy import create_engine

>>> e = create_engine("mysql://scott:tiger@localhost/test")

>>> e.pool.status()

'Pool size: 5  Connections in pool: 0 Current Overflow: -5 Current Checked out connections: 0'

>>> e.pool.checkedout()

0

>>> c1 = e.connect()

>>> e.pool.checkedout()

1

>>> e.pool.status()

'Pool size: 5  Connections in pool: 0 Current Overflow: -4 Current Checked out connections: 1'

>>> c2 = e.connect()

>>> e.pool.status()

'Pool size: 5  Connections in pool: 0 Current Overflow: -3 Current Checked out connections: 2'

>>> c1.close()

>>> e.pool.status()

'Pool size: 5  Connections in pool: 1 Current Overflow: -3 Current Checked out connections: 1'

>>> c2.close()

>>> e.pool.status()

'Pool size: 5  Connections in pool: 2 Current Overflow: -3 Current Checked out connections: 0'

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SQLAlchemy -

The Python SQL Toolkit and Object Relational Mapper

 

http://www.sqlalchemy.org/

 

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[Mike Bayer]

if you wanted to see the queue you could do this:

>>> [rec.connection for rec in e.pool._pool.queue]

[<_mysql.connection open to 'localhost' at 0x55ac3f6dfd20>, <_mysql.connection open to 'localhost' at 0x55ac3f6f52f0>]

but for more general tracking of connection pool connections you would use the event listeners and track them yourself:  https://docs.sqlalchemy.org/en/13/core/events.html#sqlalchemy.events.PoolEvents

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[Oğuzhan Kaya]

Thanks mate you are a life saver. I think you mean this about event listeners. 

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what is dbapi_conn connection_rec and connection_proxy. I couldnt get it.

def my_on_checkout(dbapi_conn, connection_rec, connection_proxy):

    "handle an on checkout event"

event.listen(Pool, 'checkout', my_on_checkout)

5 Mayıs 2020 Salı 19:52:09 UTC+3 tarihinde Mike Bayer yazdı:

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SQLAlchemy -

The Python SQL Toolkit and Object Relational Mapper

 

http://www.sqlalchemy.org/

 

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[Oğuzhan Kaya]

what is mean that checkedout checkedin connection and why When connection is closed connection in pool number increases?

5 Mayıs 2020 Salı 19:50:22 UTC+3 tarihinde Mike Bayer yazdı:

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[Mike Bayer]

the connection pool reuses connections, so when you "close" a connection, often it is recycled so that it is returned to its pooled store rather than being fully closed.

Some background on this is at https://docs.sqlalchemy.org/en/13/glossary.html#term-released

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