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https://issues.apache.org/jira/browse/HADOOP-1942?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12532313
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Raghu Angadi commented on HADOOP-1942:
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FSEditLog.java :
- in logSync() : mytxid should be set to min(id.txid, txid) otherwise, when
id.txtd is MAX_VALUE, thread could stay in logSync() for longer time (i.e. it
will always sync). This can happen when completeFile() returns false, which is
quite often.
-- Another option is not to reset id.txid but provide logSyncTillNow(), which
calls logSync() with id.txid set to current txid, if such a call is required.
- synchronized (editstream) is not required inside logEdit(). Looks like it
existed before but can be removed.
- there are two calls to System.currentTimeMillis() in side editLog().
editLog() is an in memory operation. I don't think we need to measure that.
editLog() is just like any other processing now.
I haven't looked at the Stats etc yet.
> 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
>
>
> 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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