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Memcached Example

This is a very simple example of how one might use scribl with memcached. The patch illustrates adding a counter to memcached that counts how often each key has an update operation performed on it. This is probably not super useful in real life (more likely you'd want to count key prefixes, or something else less unique than the full key name), but it illustrates the simplicity of adding scribl to an external codebase.

This example consists of two files:

  • memcached-set-counter.patch a patch against memcached.c
  • scribl-memcached_set-1240120191.log an example log generated from a memcached that was using the aforementioned patch.

The key thing to take away from this example is how minimal the patch against memcached really is. For only six additional lines of code we're able to count statistics about update operations in memcached. Additionally,

  • this is fully threadsafe; running memcached in threaded mode works fine
  • memcached commands are still O(1), since the scribl increment operation is O(1)
  • logging/serialization is happens in its own thread, which means that these operations don't block memcached (even if memcached itself is only running a single thread)