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https://issues.apache.org/jira/browse/HADOOP-1942?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12533596
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Raghu Angadi commented on HADOOP-1942:
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With 40, the best case is 20 times than before I was hoping at least 10 times.
If it is actually 40, then increase in create/deletes is less than I would
expect. I think we should get some jstacks to see where the IPC threads are
most of the time with the current config. What do the stats printed on the log
say?
> 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
> Priority: Blocker
> Fix For: 0.15.0
>
> Attachments: transactionLogSync.patch, transactionLogSync2.patch,
> transactionLogSync3.patch, transactionLogSync4.patch,
> transactionLogSync5.patch, transactionLogSync6.patch,
> transactionLogSync8.patch, transactionLogSync9.patch
>
>
> 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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