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From "Raghu Angadi (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-1942) Increase the concurrency of transaction logging to edits log
Date Wed, 10 Oct 2007 05:01:50 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1942?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12533596
] 

Raghu Angadi commented on HADOOP-1942:
--------------------------------------


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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