Alexis Midon created KAFKA-1597:
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Summary: New metrics: ResponseQueueSize and BeingSentResponses
Key: KAFKA-1597
URL: https://issues.apache.org/jira/browse/KAFKA-1597
Project: Kafka
Issue Type: New Feature
Components: core
Reporter: Alexis Midon
Priority: Minor
Attachments: KAFKA-1594_BeingSentResponses.patch,
KAFKA-1594_ResponseQueueSize.patch
This patch adds two metrics:
h3. ResponseQueueSize
As of 0.8.1, the sizes of the response queues are [reported as different
metrics|https://github.com/apache/kafka/blob/0.8.1/core/src/main/scala/kafka/network/RequestChannel.scala#L127-L134]
- one per processor thread. This is not very ideal for different reasons:
* charts have to sum the different metrics
* the metrics collection system might not support 'wild card queries' like
{{sum:kafka.network.RequestChannel.Processor_*_ResponseQueueSize}} in which
case monitoring now depends on the number of configured network threads
* monitoring the response by thread is not very valuable. However the global
number of responses is useful.
* proposal*
So this patch exposes the total number of queued responses as a metric
{{ResponseQueueSize}}
*implementation*
In {{RequestChannel}}, create a Gauge that adds up the size of the response
queues.
h3. BeingSentResponses
As of 0.8.1, the processor threads will poll responses from the queues and
attach them to the SelectionKey as fast as possible. The consequence of that is
that the response queues are not a good indicator of the number of "in-flight"
responses. The {{ServerSocketChannel}} acting as another queue of response to
be sent.
The current metrics don't reflect the size of this "buffer", which is an issue.
*proposal*
This patch adds a gauge that keeps track of the number of responses being
handled by the {{ServerSocketChannel}}.
That new metric is named "BeingSentResponses" (who said naming was hard?)
*implementation*
To calculate that metric, the patch adds up the number of SelectionKeys
interested in writing, across processor threads.
Another approach could be to keep all in-flight responses in a data structure
(let's say a map) shared by the processor threads. A response will be added to
that map when dequeued from the response queue, and removed when the write is
complete. The gauge will simply report the size of that map. I decided against
that second approach as it is more intrusive and requires some additional
bookkeeping to gather information already available through the
{{SelectionKey}}'s
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