Hello!

I need to create a global atomic counter (64-bit) in my AppEngine/J
app. Like

long count = MyCounter.increment()

that will 100% guarantee that count will never ever be the same for
two different requests, and that I will be able to increment it
several million times/day initially, and much more if/when traffic
increases. I do not really care if it skips a number or two
occasionally: I can live with it returning a value larger than the
actual number of calls, but I do need absolute uniqueness and
reasonably linear growth (i.e. is two consecutive calls from a client
should result in ascending counter values).

Is this possible to do with Google AppEngine? Sharded counters can
ensure consistent counting, but not unique counts; memcache counters
can ensure unique increments, but they are perishable and thus
difficult (impossible?) to properly synchronize with persistent
storage. Using one entity to read-update in a transaction will not
scale...

Thanks,
MG

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