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https://issues.apache.org/jira/browse/HDFS-6782?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Junping Du updated HDFS-6782:
-----------------------------
Target Version/s: (was: 2.8.0)
> Improve FS editlog logSync
> --------------------------
>
> Key: HDFS-6782
> URL: https://issues.apache.org/jira/browse/HDFS-6782
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: namenode
> Affects Versions: 2.4.1
> Reporter: Yi Liu
> Assignee: Yi Liu
> Attachments: HDFS-6782.001.patch, HDFS-6782.002.patch
>
>
> In NN, it uses a double buffer (bufCurrent, bufReady) for log sync,
> bufCurrent it to buffer new coming edit ops and bufReady is for flushing.
> This's efficient. When flush is ongoing, and bufCurrent is full, NN goes to
> force log sync, and all new Ops are blocked (since force log sync is
> protected by FSNameSystem write lock). After the flush finished, the new Ops
> are still blocked, but actually at this time, bufCurrent is free and Ops can
> go ahead and write to the buffer. The following diagram shows the detail.
> This JIRA is for this improvement. Thanks [~umamaheswararao] for confirming
> this issue.
> {code}
> edit1(txid1) ------ write to bufCurrent -------- logSync --------- (swap
> buffer)flushing -------
> edit2(txid2) ------ write to bufCurrent -------- logSync --------- waiting
> -------
> edit3(txid3) ------ write to bufCurrent -------- logSync --------- waiting
> -------
> edit4(txid4) ------ write to bufCurrent -------- logSync --------- waiting
> -------
> edit5(txid5) ------ write to bufCurrent --full-- force sync --------- waiting
> -------
> edit6(txid6) ------ blocked
> ...
> editn(txidn) ------ blocked
> {code}
> After the flush, it becomes
> {code}
> edit1(txid1) ------ write to bufCurrent -------- logSync --------- finished
> --------
> edit2(txid2) ------ write to bufCurrent -------- logSync --------- flushing
> -------
> edit3(txid3) ------ write to bufCurrent -------- logSync --------- waiting
> -------
> edit4(txid4) ------ write to bufCurrent -------- logSync --------- waiting
> -------
> edit5(txid5) ------ write to bufCurrent --full-- force sync --------- waiting
> -------
> edit6(txid6) ------ blocked
> ...
> editn(txidn) ------ blocked
> {code}
> After edit1 finished, bufCurrent is free, and the thread which flushes txid2
> will also flushes txid3-5, so we should return from the force sync of edit5
> and FSNamesystem write lock will be freed (Don't worry that edit5 Op will
> return, since there will be a normal logSync after the force logSync and
> there will wait for sync finished). This is the idea of this JIRA.
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