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https://issues.apache.org/jira/browse/HADOOP-1942?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12531172
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Raghu Angadi commented on HADOOP-1942:
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Looks like this patch has the same locking issue as before. But it would be
nice to gather stats with this implementation and compare with new stats once
we fix it.
> 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
>
>
> 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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