Guanghao Zhang created HBASE-15885:
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             Summary: Compute StoreFile HDFS Blocks Distribution when need it
                 Key: HBASE-15885
                 URL: https://issues.apache.org/jira/browse/HBASE-15885
             Project: HBase
          Issue Type: Improvement
          Components: HFile
    Affects Versions: 2.0.0
            Reporter: Guanghao Zhang


Now when open a StoreFileReader, it always need to compute HDFS blocks 
distribution. But when balance a region, it will increase the region not 
serving time. Because it need first close region on rs A, then open it on rs B. 
When close region, it first preFlush, then flush the new update to a new store 
file. The new store file will first be flushed to tmp directory, then move it 
to column family directory. These need open StoreFileReader twice which means 
it need compute HDFS blocks distribution twice. When open region on rs B, it 
need open StoreFileReader and compute HDFS blocks distribution too. So when 
balance a region, it need compute HDFS blocks distribution three times for per 
new store file. This will increase the region not serving time and we don't 
need compute HDFS blocks distribution when close a region.

The related three methods in HStore.
1. validateStoreFile(...)
2. commitFile(...)
3. openStoreFiles(...)



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