Resetable counter

[krukru]

I couldn't find a way to reset the counter values to zero (since they persist in Redis/APC) so I added a reset method.

[bracki]

What's your use case for resetting counters?

[krukru]

For example, we keep track of the number of successful/failed http requests since the last server restart. I guess that this could be handled with a workaround (labels), but it seemed just practical to reset the counters on a server crash and start counting again from 0.

[bracki]

Ah, so you want to reset metrics in Redis, correct? Because with APC they would automatically be resetted.

[krukru]

Right, APC would be reset since it is not persistent. But Redis (and a theoretical File Storage adapter) would require this to be reset.

[bracki]

OK, but wouldn't it make sense than to add this to every possible metric?

[krukru]

Well, you are right on that account :)
If you think this is a good PR I can update it to include other metrics as well (not just Counter)

[jitendra-1217]

But how does it matter to prometheus, it anyway handles counter resets doing some normalisation, right?
I am just curious how do you end up using this data.