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()