Caching despite low threshold

[gerases]

Hi,

I have the following caching configuration now:

cache:
   # Type of caching. Valid: "mem", "memcache", "null"
   type: "mem"
   # Cache limit in megabytes
   size_mb: 0
   # Default cache timeout value. Identical to DEFAULT_CACHE_DURATION in graphite-web.
   defaultTimeoutSec: 10

Despite that, the new metrics are not discovered until about 30 minutes later. Is there something I'm missing in the configuration? What's a good way to troubleshoot this?

Thanks!