Cassandra multiprocessing can't pickle _thread.lock objects
Daiyue Weng
daiyueweng at gmail.com
Tue Jun 21 10:10:33 EDT 2016
I tried to use Cassandra and multiprocessing to insert rows (dummy data)
concurrently based on the examples in
http://www.datastax.com/dev/blog/datastax-python-driver-multiprocessing-example-for-improved-bulk-data-throughput
This is my code
class QueryManager(object):
concurrency = 100 # chosen to match the default in execute_concurrent_with_args
def __init__(self, session, process_count=None):
self.pool = Pool(processes=process_count, initializer=self._setup,
initargs=(session,))
@classmethoddef _setup(cls, session):
cls.session = session
cls.prepared = cls.session.prepare("""
INSERT INTO test_table (key1, key2, key3, key4, key5) VALUES (?, ?, ?, ?, ?)
""")
def close_pool(self):
self.pool.close()
self.pool.join()
def get_results(self, params):
results = self.pool.map(_multiprocess_write,
(params[n:n+self.concurrency] for n in range(0, len(params),
self.concurrency)))
return list(itertools.chain(*results))
@classmethoddef _results_from_concurrent(cls, params):
return [results[1] for results in
execute_concurrent_with_args(cls.session, cls.prepared, params)]
def _multiprocess_write(params):
return QueryManager._results_from_concurrent(params)
if __name__ == '__main__':
processes = 2
# connect cluster
cluster = Cluster(contact_points=['127.0.0.1'], port=9042)
session = cluster.connect()
# database name is a concatenation of client_id and system_id
keyspace_name = 'unit_test_0'
# drop keyspace if it already exists in a cluster
try:
session.execute("DROP KEYSPACE IF EXISTS " + keyspace_name)
except:
pass
create_keyspace_query = "CREATE KEYSPACE " + keyspace_name \
+ " WITH replication = {'class':
'SimpleStrategy', 'replication_factor': '1'};"
session.execute(create_keyspace_query)
# use a session's keyspace
session.set_keyspace(keyspace_name)
# drop table if it already exists in the keyspace
try:
session.execute("DROP TABLE IF EXISTS " + "test_table")
except:
pass
# create a table for invoices in the keyspace
create_test_table = "CREATE TABLE test_table("
keys = "key1 text,\n" \
"key2 text,\n" \
"key3 text,\n" \
"key4 text,\n" \
"key5 text,\n"
create_invoice_table_query += keys
create_invoice_table_query += "PRIMARY KEY (key1))"
session.execute(create_test_table)
qm = QueryManager(session, processes)
params = list()
for row in range(100000):
key = 'test' + str(row)
params.append([key, 'test', 'test', 'test', 'test'])
start = time.time()
rows = qm.get_results(params)
delta = time.time() - start
log.info(fm('Cassandra inserts 100k dummy rows for ', delta, ' secs'))
when I executed the code, I got the following error
TypeError: can't pickle _thread.lock objects
which pointed at
self.pool = Pool(processes=process_count, initializer=self._setup,
initargs=(session,))
I am wondering how to resolve the issue.
cheers
More information about the Python-list
mailing list