Cameron Zemek created CASSANDRA-17175:
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Summary: More detailed latency metrics
Key: CASSANDRA-17175
URL: https://issues.apache.org/jira/browse/CASSANDRA-17175
Project: Cassandra
Issue Type: New Feature
Reporter: Cameron Zemek
Attachments: request_latency_metric.patch
There is a disconnect with latency clients experience and the latency reported
by Cassandra. For example read latency only measures the latency of the
StorageProxy::readRows call.
None of the time spent sitting in the Native Transport queue is measured.
Neither is any of the time for writing the response back to the channel.
Dispatcher processRequest keep track of when if first starts processing the
request but best I can tell this is only used in tracking for timeouts.
It would be useful for tracking down cause of high client latency if there was
more detailed cassandra metrics around it.
I have attached a patch that adds latency tracking higher in the call stack.
Starting timer from before its put into the Native Transport Request executor.
The patch gives 3 different metrics per Request type:
delay - measures time from when its submitted to NTR pool till it call
processRequest
process - time spent in the Dispatcher processRequest call
total - time from when first submitted to NTR pool until the response has been
flushed
This patch may not be cleanest or best way of doing this but hopefully gives an
idea of what I think would be useful addition that will help operators diagonse
latency issues.
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