Cache Stats for Varnish and Memcached
The hit rate and the numbers behind it
How well your cache works
A running Varnish or Memcached service has a Stats button. It opens a live snapshot of that cache: the hit rate first, then the numbers behind it.
Where: Services › System Services › the Varnish or Memcached card › Stats
01 · Cache hit rate
The big number is the share of requests answered from the cache: hits divided by hits plus misses. It reads N/A until the cache has had traffic.
All counters run since the service last started, and the dialog says how long ago that was. A restart sets them back to zero.
02 · Varnish
| Row | What it means |
|---|---|
| Client requests | Requests from visitors. |
| Cache hits | Requests answered from the cache, without asking your site. |
| of which grace hits | Slightly stale pages served at once while a fresh copy was fetched in the background. |
| Cache misses | Requests that had to be fetched from your site. |
| Backend requests | Requests sent to your site: misses plus pages that are never cached. |
| Backend failures | Failed fetches from your site. Should be 0. |
| Objects in cache | Pages and files stored right now. |
| Expired objects | Objects removed at the end of their lifetime. Normal. |
| LRU nuked objects | Objects thrown out early to make room. Often above 0 means the cache is too small. |
| Sessions dropped | Visitor connections dropped for lack of a worker. Should be 0. |
| Memory used | Cache memory in use, of the total. |
| Allocator failures | Failed memory allocations. Should be 0. |
| Worker threads | Threads ready to serve visitors. |
03 · Memcached
| Row | What it means |
|---|---|
| Get requests | Reads. |
| Set requests | Writes. |
| Get hits | Reads that found their key. |
| Get misses | Reads for keys not in the cache: never stored, expired or evicted. |
| Objects in cache | Items stored right now. |
| Objects ever stored | Items stored since start, replaced and expired ones included. |
| Memory used | Memory used by items, of the memory limit. |
| Evictions | Items thrown out early to make room. Often above 0 means the limit is too small. |
| Expired unfetched | Items that expired without ever being read. |
| Connections | Connections open now, and accepted since start. |
Every row has an info icon: hover it for the explanation. Refresh in the dialog takes a new snapshot.