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From "Liyin Tang (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-7266) [89-fb] Using pread for non-compaction read request
Date Tue, 04 Dec 2012 00:25:58 GMT
Liyin Tang created HBASE-7266:
---------------------------------

             Summary: [89-fb] Using pread for non-compaction read request
                 Key: HBASE-7266
                 URL: https://issues.apache.org/jira/browse/HBASE-7266
             Project: HBase
          Issue Type: Improvement
            Reporter: Liyin Tang


There are 2 kinds of read operations in HBase: pread and seek+read.
Pread, positional read, is stateless and create a new connection between the DFSClient and
DataNode for each operation. While seek+read is to seek to a specific postion and prefetch
blocks from data nodes. The benefit of seek+read is that it will cache the prefetch result
but the downside is it is stateful and needs to synchronized.

So far, both compaction and scan are using pread, which caused some resource contention. So
using the pread for the scan request can avoid the resource contention. In addition, the region
server is able to do the prefetch for the scan request (HBASE-6874) so that it won't be necessary
to let the DFSClient to prefetch the data any more.

I will run through the scan benchmark (with no block cache) with verify the performance.

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