Tianying Chang created HBASE-16027:
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             Summary: All Regions are flushed at about same time when 
MEMSTORE_PERIODIC_FLUSH is on, causing flush spike
                 Key: HBASE-16027
                 URL: https://issues.apache.org/jira/browse/HBASE-16027
             Project: HBase
          Issue Type: Bug
          Components: hbase, Performance
    Affects Versions: 1.2.1
            Reporter: Tianying Chang
            Assignee: Tianying Chang


In our production cluster, we observed that memstore flush spike every hour for 
all regions/RS. (we use the default memstore periodic flush time of 1 hour). 

This will happend when two conditions are met: 
1. the memstore does not have enough data to be flushed before 1 hour limit 
reached;
2. all regions are opened around the same time, (e.g. all RS are started at the 
same time when start a cluster). 

With above two conditions, all the regions will be flushed around the same time 
at: startTime+1hour-delay again and again.

We added a flush jittering time to randomize the flush time of each region, so 
that they don't get flushed at around the same time. We had this feature 
running in our 94.7 and 94.26 cluster. Recently, we upgrade to 1.2, found this 
issue still there in 1.2. So we are porting this into 1.2 branch. 



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