I recently learned about the Current cache hit ratio log message in dispatcher logs.
But I can't find any good documentation on it. So I have a few questions:
Over what timeframe is the ratio calculated? Is it from Apache startup?
Does the calculation ignore those paths that are configured to never cache in the dispatcher?
I ask because I have an existing access log query that calculates the difference between dispatcher requests and publish instance requests only on paths where I know there is caching. I ignore servlet paths that do no caching, and I also ignore all requests other than 200s. With that calculation I get a higher hit ratio than what the dispatcher claims.
How much should I trust the dispatcher log calculation?
The ratio is calculated as (100 * req_hits / req_total) with
req_hits = # files delivered from cache
req_total = the total number of requests handled by the dispatcher
from this point of view the cache-hit ratio is the same if requests are blocked on dispatcher (not httpd!) or forwarded to publish. So the number is nice, but it's hard to draw meaningful conclusions from it.