Hello,

I have implemented a variation of the sharded counter form Google IO speech (http://sites.google.com/site/io/building-scalable-web- applications-with-google-app-engine)

My variation is that instead of haveing a fixed number my number of shards increases if contention on the counter increases.

But I am not quite sure if I have done it right: Please have a look:

def inc(self): try: def txn(): c = self._get_one() # get sharded counter by random c.count += 1 # increase counter c.put() # write counter try: db.run_in_transaction(txn) except db.TransactionFailedError(): # if this transaction fails... logging.debug('Counter %s: inc failed.' % self.name) self.num_shards += 5 # increase number of shards self.put() except: pass

You see, when the transaction fails due to high contention I modify the number of shards. But I am not sure, if I should place this

self.num_shards += 5 # increase number of shards self.put()

inside a transaction or not...? I mean if contention is high a lot threads are going to try to increase the number of shards. Is it correct to ignore the case when this code fails (the outer try/except block) or should it be placed inside a transaction (which would leed to retries of this code)?

Regards, Constantin