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https://issues.apache.org/jira/browse/HDFS-14349?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16794201#comment-16794201
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star commented on HDFS-14349:
-----------------------------
The autoroll operation is executed in ANN service, not triggered by SNN.
So it will not degrade NN performance with more SNN.
Related code FSNamesystem:
{code:java}
//Active Service
void startActiveServices() throws IOException {
...
nnEditLogRoller = new Daemon(new NameNodeEditLogRoller(
editLogRollerThreshold, editLogRollerInterval));
nnEditLogRoller.start();
...
}
//Auto roll log
long numEdits = getCorrectTransactionsSinceLastLogRoll();
if (numEdits > rollThreshold) {
FSNamesystem.LOG.info("NameNode rolling its own edit log because"
+ " number of edits in open segment exceeds threshold of "
+ rollThreshold);
rollEditLog();
}
{code}
> Edit log may be rolled more frequently than necessary with multiple Standby
> nodes
> ---------------------------------------------------------------------------------
>
> Key: HDFS-14349
> URL: https://issues.apache.org/jira/browse/HDFS-14349
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: ha, hdfs, qjm
> Reporter: Erik Krogen
> Assignee: Ekanth Sethuramalingam
> Priority: Major
>
> When HDFS-14317 was fixed, we tackled the problem that in a cluster with
> in-progress edit log tailing enabled, a Standby NameNode may _never_ roll the
> edit logs, which can eventually cause data loss.
> Unfortunately, in the process, it was made so that if there are multiple
> Standby NameNodes, they will all roll the edit logs at their specified
> frequency, so the edit log will be rolled X times more frequently than they
> should be (where X is the number of Standby NNs). This is not as bad as the
> original bug since rolling frequently does not affect correctness or data
> availability, but may degrade performance by creating more edit log segments
> than necessary.
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