I am using the sqlalchemy package in python. I have an operation that takes some time to execute after I perform an autoload on an existing table. This causes the following error when I attempt to use the connection:
sqlalchemy.exc.OperationalError: (OperationalError) (2006, 'MySQL server has gone away')
I have a simple utility function that performs an insert many:
def insert_data(data_2_insert, table_name):
engine = create_engine('mysql://blah:blah123@localhost/dbname')
# Metadata is a Table catalog.
metadata = MetaData()
table = Table(table_name, metadata, autoload=True, autoload_with=engine)
for c in mytable.c:
print c
column_names = tuple(c.name for c in mytable.c)
final_data = [dict(zip(column_names, x)) for x in data_2_insert]
ins = mytable.insert()
conn = engine.connect()
conn.execute(ins, final_data)
conn.close()
It is the following line that times long time to execute since 'data_2_insert' has 677,161 rows.
final_data = [dict(zip(column_names, x)) for x in data_2_insert]
I came across this question which refers to a similar problem. However I am not sure how to implement the connection management suggested by the accepted answer because robots.jpg pointed this out in a comment:
Note for SQLAlchemy 0.7 - PoolListener is deprecated, but the same solution can be implemented using the new event system.
If someone can please show me a couple of pointers on how I could go about integrating the suggestions into the way I use sqlalchemy I would be very appreciative. Thank you.
I think you are looking for something like this:
from sqlalchemy import exc, event
from sqlalchemy.pool import Pool
@event.listens_for(Pool, "checkout")
def check_connection(dbapi_con, con_record, con_proxy):
'''Listener for Pool checkout events that pings every connection before using.
Implements pessimistic disconnect handling strategy. See also:
http://docs.sqlalchemy.org/en/rel_0_8/core/pooling.html#disconnect-handling-pessimistic'''
cursor = dbapi_con.cursor()
try:
cursor.execute("SELECT 1") # could also be dbapi_con.ping(),
# not sure what is better
except exc.OperationalError, ex:
if ex.args[0] in (2006, # MySQL server has gone away
2013, # Lost connection to MySQL server during query
2055): # Lost connection to MySQL server at '%s', system error: %d
# caught by pool, which will retry with a new connection
raise exc.DisconnectionError()
else:
raise
If you wish to trigger this strategy conditionally, you should avoid use of decorator here and instead register listener using listen()
function:
# somewhere during app initialization
if config.check_connection_on_checkout:
event.listen(Pool, "checkout", check_connection)
More info:
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With