The reason sharding works to reduce contention is that the each shard is in a separate entity group. Within the transaction, one GeneralCounterShard entity is either retrieved or written. Each shard forms its own entity group, which is what you want so there's no contention on writes.
On Jul 13, 4:36 pm, Nathan Gray <[email protected]> wrote: > I'm confused. I thought that you could only get/put entities from one > entity group in a transaction, but the example code for sharded > counters doesn't put its shards into a common entity group: > > def increment(name): > """Increment the value for a given sharded counter. > > Parameters: > name - The name of the counter > """ > config = GeneralCounterShardConfig.get_or_insert(name, name=name) > def txn(): > index = random.randint(0, config.num_shards - 1) > shard_name = name + str(index) > counter = GeneralCounterShard.get_by_key_name(shard_name) > if counter is None: > counter = GeneralCounterShard(key_name=shard_name, name=name) > counter.count += 1 > counter.put() > db.run_in_transaction(txn) > memcache.incr(name) > > Note that the GeneralCounterShard(...) constructor call doesn't set > the entity's parent. > > What's up with that? > > Thanks, > -n8 > > --http://n8gray.org --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Google App Engine" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en -~----------~----~----~----~------~----~------~--~---
