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From "Vikas Vishwakarma (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-19236) Tune client backoff trigger logic and backoff time in ExponentialClientBackoffPolicy
Date Fri, 10 Nov 2017 06:48:00 GMT
Vikas Vishwakarma created HBASE-19236:
-----------------------------------------

             Summary: Tune client backoff trigger logic and backoff time in ExponentialClientBackoffPolicy
                 Key: HBASE-19236
                 URL: https://issues.apache.org/jira/browse/HBASE-19236
             Project: HBase
          Issue Type: Improvement
            Reporter: Vikas Vishwakarma


We were evaluating the ExponentialClientBackoffPolicy (HBASE-12986) for implementing basic
service protection, usage quota allocation for few heavy loading clients, especially M/R job
based HBase clients. However it was observed that ExponentialClientBackoffPolicy slows down
the client dramatically even when there is not much load on the HBase cluster. 
For a simple multithreaded write throughput client without enabling ExponentialClientBackoffPolicy
was able to complete in less than 5 mins running on a 40 node cluster (~100G data). 
The same client took ~10 hours to complete with ExponentialClientBackoffPolicy enabled with
default settings DEFAULT_MAX_BACKOFF of 5 mins
Even after reducing the DEFAULT_MAX_BACKOFF of 1 min, the client took ~2 hours to complete
Current ExponentialClientBackoffPolicy decides the backoff time based on 3 factors 
    // Factor in memstore load
    double percent = regionStats.getMemstoreLoadPercent() / 100.0;

    // Factor in heap occupancy
    float heapOccupancy = regionStats.getHeapOccupancyPercent() / 100.0f;

    // Factor in compaction pressure, 1.0 means heavy compaction pressure
    float compactionPressure = regionStats.getCompactionPressure() / 100.0f;

However according to our test observations it looks like the client backoff is getting triggered
even when there is hardly any load on the cluster. We need to evaluate the existing logic
or probably implement a different policy more customized and suitable to our needs. 

One of the ideas is to base it directly on compactionQueueLength instead of heap occupancy
etc. Consider a case where there is high throughput write load and the compaction is still
able keep up with the rate of memstore flushes and compact all the files being flushed at
the same rate. In this case memstore can be full and heap occupancy can be high but still
it is not necessary indicator that the service is falling behind on processing the client
load and there is a need to backoff the client as we are just utilizing the full write throughput
of the system which is good. However if the compactionQueue starts building up and is continuously
above a threshold and increasing then that is a reliable indicator that the system is not
able to keep up with the input load and  is slowly falling behind. 



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