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From "Mukund Madhugiri (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-1942) Increase the concurrency of transaction logging to edits log
Date Tue, 09 Oct 2007 22:52:53 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1942?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12533538
] 

Mukund Madhugiri commented on HADOOP-1942:
------------------------------------------

I ran NNBench on a 500 node cluster and here is the comparison data

trunk:
CreateWrite: 924 TPS
OpenRead: 58892 TPS
Delete: 766 TPS

trunk + patch:
CreateWrite: 2520 TPS
OpenRead: 54831 TPS
Delete: 1993 TPS

> 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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