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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] Created: (HADOOP-1942) Increase the concurrency of transaction logging to edits log
Date Tue, 25 Sep 2007 06:04:50 GMT
Increase the concurrency of transaction logging to edits log
------------------------------------------------------------

                 Key: HADOOP-1942
                 URL: https://issues.apache.org/jira/browse/HADOOP-1942
             Project: Hadoop
          Issue Type: Improvement
          Components: dfs
            Reporter: dhruba borthakur
            Assignee: dhruba borthakur
             Fix For: 0.15.0


For some typical workloads, the throughput of the namenode is bottlenecked by the rate of
transactions that are being logged into tghe edits log. In the current code, a batching scheme
implies that all transactions do not have to incur a sync of the edits log to disk. However,
the existing batch-ing scheme can be improved.

One option is to keep two buffers associated with edits file. Threads write to the primary
buffer while holding the FSNamesystem lock. Then the thread release the FSNamesystem lock,
acquires a new lock called the syncLock, swaps buffers, and flushes the old buffer to the
persistent store. Since the buffers are swapped, new transactions continue to get logged into
the new buffer. (Of course, the new transactions cannot complete before this new buffer is
sync-ed).

This approach does a better job of batching syncs to disk, thus improving performance.



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