memcached counters missing in action

[Brad Fitzpatrick]

What's a counter?

memcached has no such object.

I assume the Java client gives you such an abstraction.  In any case,
they're not magic.  They die like the rest.

- Brad


On Fri, 24 Mar 2006, Charlie Spurr wrote:

> I'm using memcached counters to track budget balances and
> I'm seeing some of the counters mysteriously disappear
> from the cache sometime after a decr of the counter.
>
> Here's what I'm doing for each counter:
> a) At application startup on the primary app server, I
>     load the current remaining balance for each budget
>     from a MySQL database into a memcached counter using
>     the Java MemCachedClient's storeCounter(String key,
>     long value) method.
>
> b) As billable events occur asynchronously, I call the client's
>     decr(String key, long amount) method to decrement the
>     remaining balance in the cache.
>
> c) In a synchronization thread (one per app server, ten total),
>     I call the MemCachedClient's getCounter(String key) method
>     to retrieve the cached budget balance and sync it back to
>     the database.
>
> This seems to run fine for a while until getCounter or decr calls
> start to hit "MemCached.MemCachedClient - counter not found at key:"
> errors. When this occurs, MemCachedClient's keyExists(String key)
> calls return true but getCounter or decr calls fail with this error.
>
> My questions are:
> 1) Do counters expire like Object data expire or are they expected
>     to remain in the cache until they are deleted or flushed?
>
> 2) If counters expire, how do I set their expiration time? There is no
>     version of MemCachedClient's storeCounter that takes a expire Date
>     parameter. Should I be using MemCachedClient's  set(String key,
>     Object value, Date expiry) instead of (or in combination with)
>     storeCounter?
>
> 3) Shouldn't MemCachedClient's keyExists(String key) return false
>     when calls to getCounter or decr calls fail with "counter not
>     found at key:" errors?
>
> Charlie Spurr
> Kayak.com
>
>