Question

For examples,

First instance maintains a count-variable (init value is 0), after it served 10 requests, count increased to 10.
Then there is no more request thus app engine shuts down the first instance.

After that, the second instance is created to serve incoming requests.

My question is the count-variable will be 10 or reseted to init value (0) ?

If it is reseted, is there anyway to avoid that ? (Beside using datastore manually )?

Thank you

Answer 1

I presume you’re talking about a global/module-level variable that is incremented by each request. The answer is that each instance runs in its own process, so not only will subsequent instances start at zero, but since you can have multiple instances running at the same time, each of them will have their own independent counters.

The proper way to do this is to use memcache to store the key, which will be a single value across all instances. You can do memcache.incr('counter') to increment the value atomically.

If persisting the data is important, you could look into storing sharded counters.