Increment on invalid value

[minad]

Hi Evan,

from the last issue #109 I thought that you already looked at my code. Is it correct that memcached returns 0 if increment is applied on an invalid value?

I want to throw an exception in such a case, see:

https://github.com/minad/moneta/blob/master/lib/moneta/adapters/memcached/native.rb#L56

Thx!

Daniel

[evan]

I believe it destructively changes the value to the ASCII string "0", thus letting you increment it correctly in the future.

I'm not sure if throwing an error is correct as one could be incrementing and decrementing and arrive at 0 legitimately.

[minad]

Hi evan, I think you misunderstood the issue a bit. Memcached doesn't destructivily change the ascii string to 0. But it always returns 0 in such a case. I would say this is incorrect behaviour, memcached should throw an error since currently you can not distinguish valid 0 and invalid 0.

Dalli and redis for example throw an error.

[minad]

Another possibility would be to return nil or the ascii string, at least it shouldn't return 0. An exception would be the best imho. Reopen?

[minad]

Ok, I investigated this a bit and it seems to be a problem of the c memcached library. The library returns 0 in the case of an invalid increment.

server.set('counter', 'invalid')
server.get('counter') # => invalid
server.increment('counter')  # => 0
server.get('counter') # => invalid

[evan]

Oh, ok. Well, I will reopen. Can you submit a patch for the bundled C library?

[minad]

Hmm, better for the upstream library. But I am not in the source there. Will do if I have time, ok?

[evan]

We're already far diverged from the original upstream package, so you'll have to just do it here.

Sounds good.

[minad]

ok, why is that? That is bad.

[evan]

Upstream performance degraded unacceptably. There are a few tickets discussing the problem.