Jeffrey Zhong created HBASE-11314:
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             Summary: Remove MultiVersionConsistencyControl#writeQueue
                 Key: HBASE-11314
                 URL: https://issues.apache.org/jira/browse/HBASE-11314
             Project: HBase
          Issue Type: Improvement
            Reporter: Jeffrey Zhong
             Fix For: 0.99.0


This is a follow up improvement of HBase-8763. After we combined MVCC & 
LogSeqId, the memstore read point advances in the logSeqId increasing order. 
The MultiVersionConsistencyControl#writeQueue can be possibly removed.

In order to remove writeQueue, we need to return the disruptor sequence of the 
last WALEdit with durability >= SYNC_WAL inside disruptor consumer code before 
assigning log sequence Id. If current WALEdit has durability >= SYNC_WAL, we 
return the disruptor sequence of current WALEdit.

During syncOrDefer, we always waits for the sequence of the last WALEdit has 
durability >= SYNC_WAL.

The tricky part is how to return the disruptor sequence of the last WALEdit 
with durability >= SYNC_WAL cleanly from disruptor consumer. 

We could put those info in HLogKey because we always create a new HLogKey 
object for each change otherwise we have to create a new object for this 
purpose.




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