Kannan Muthukkaruppan created HBASE-7011:
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             Summary: log rolling and cache flushing should be able to proceed 
in parallel
                 Key: HBASE-7011
                 URL: https://issues.apache.org/jira/browse/HBASE-7011
             Project: HBase
          Issue Type: Improvement
            Reporter: Kannan Muthukkaruppan


Today, during a memstore flush (snapshot of memstore + flushing to disk), log 
rolling cannot happen. This seems like a bad design, and an unnecessary 
restriction. 

Possible reasons cited for this in code are:
(i) maintenance of the lastSeqWritten map.
(ii) writing a "completed-cache-flush" marker into the same log before the roll.

It seems that we can implement a new design for (i) to avoid holding the lock 
for the entire duration of the flush. And the motivation for (ii) is not even 
clear. We should reason this out, and make sure we can relax the restriction. 
[See related discussion in HBASE-6980.]


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