Advanced Session Pool Topics¶
Custom Session Pool Implementations¶
You can supply your own pool implementation, which must satisfy the
contract laid out in
AbstractSessionPool:
from google.cloud.spanner import AbstractSessionPool
class MyCustomPool(AbstractSessionPool):
def __init__(self, custom_param):
super(MyCustomPool, self).__init__()
self.custom_param = custom_param
def bind(self, database):
...
def get(self, read_only=False):
...
def put(self, session, discard_if_full=True):
...
pool = MyCustomPool(custom_param=42)
database = instance.database(DATABASE_NAME, pool=pool)
Lowering latency for read / query operations¶
Some applications may need to minimize latency for read operations, including
particularly the overhead of making an API request to create or refresh a
session. PingingPool is designed for such
applications, which need to configure a background thread to do the work of
keeping the sessions fresh.
Create an instance of PingingPool:
from google.cloud.spanner import Client, PingingPool
client = Client()
instance = client.instance(INSTANCE_NAME)
pool = PingingPool(size=10, default_timeout=5, ping_interval=300)
database = instance.database(DATABASE_NAME, pool=pool)
Set up a background thread to ping the pool’s session, keeping them from becoming stale:
import threading
def background_loop():
while True:
# (Optional) Perform other background tasks here
pool.ping()
background = threading.Thread(target=background_loop, name='ping-pool')
background.daemon = True
background.start()
Lowering latency for mixed read-write operations¶
Some applications may need to minimize latency for read write operations,
including particularly the overhead of making an API request to create or
refresh a session or to begin a session’s transaction.
TransactionPingingPool is designed for
such applications, which need to configure a background thread to do the work
of keeping the sessions fresh and starting their transactions after use.
Create an instance of
TransactionPingingPool:
from google.cloud.spanner import Client, TransactionPingingPool
client = Client()
instance = client.instance(INSTANCE_NAME)
pool = TransactionPingingPool(size=10, default_timeout=5, ping_interval=300)
database = instance.database(DATABASE_NAME, pool=pool)
Set up a background thread to ping the pool’s session, keeping them from becoming stale, and ensuring that each session has a new transaction started before it is used:
import threading
def background_loop():
while True:
# (Optional) Perform other background tasks here
pool.ping()
pool.begin_pending_transactions()
background = threading.Thread(target=background_loop, name='ping-pool')
background.daemon = True
background.start()
