[ https://issues.apache.org/jira/browse/CASSANDRA-6591?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14041400#comment-14041400 ]
Benedict commented on CASSANDRA-6591: ------------------------------------- Apologies for the delay on this. I think this ticket does slightly fit into a wider discussion, though here we're using a Meter instead of a Histogram/Timer (where codahale is much more broken by default). The Meters *are* still costlier to keep around and maintain than we might otherwise like: each meter maintains a LongAdder (which is in principle to avoid contention, but for our use case just means more cpu-cache misses), but more importantly maintains *four* LongAdders per meter, so each time we attempt to hit the cache we must update at least 8 LongAdders (since we update two meters here). I would prefer to see us moving to a scheme that uses only two AtomicLong for this data, but I'm not sure we need to hold up this ticket for that. However I would say we only need to maintain *either* hits *or* misses, since even for a rate property, misses = total - hits, so we can define our misses as a simple Gauge returning requests - hits > un-deprecate cache recentHitRate and expose in o.a.c.metrics > ------------------------------------------------------------ > > Key: CASSANDRA-6591 > URL: https://issues.apache.org/jira/browse/CASSANDRA-6591 > Project: Cassandra > Issue Type: Improvement > Components: Core > Reporter: Chris Burroughs > Assignee: Chris Burroughs > Priority: Minor > Attachments: j6591-1.2-v1.txt, j6591-1.2-v2.txt, j6591-1.2-v3.txt > > > recentHitRate metrics were not added as part of CASSANDRA-4009 because there > is not an obvious way to do it with the Metrics library. Instead hitRate was > added as an all time measurement since node restart. > This does allow changes in cache rate (aka production performance problems) > to be detected. Ideally there would be 1/5/15 moving averages for the hit > rate, but I'm not sure how to calculate that. Instead I propose updating > recentHitRate on a fixed interval and exposing that as a Gauge. -- This message was sent by Atlassian JIRA (v6.2#6252)