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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HADOOP-1942) Increase the concurrency of transaction logging to edits log
Date Thu, 04 Oct 2007 06:15:50 GMT

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

dhruba borthakur updated HADOOP-1942:
-------------------------------------

    Attachment: transactionLogSync5.patch

Merged patch with latest trunk. I also removed resetting the ThreadLocal txid in logSync().
In future, if we need to implement logSyncTillNow() then we can implement that part of it.
I also think that the time measurement to write the transaction into memory (logEdit) might
be helpful. Espeically, if in future we decide to compare transaction log resident in ram
vs. nvram. The two calls to retrieve system time should not add much overhead. 

About removing the "synchronized (editStream)": this one makes sense, but let me ponder over
it for a day.

> 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
>
>
> 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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