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https://issues.apache.org/jira/browse/HDFS-14317?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16785002#comment-16785002
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Ekanth Sethuramalingam edited comment on HDFS-14317 at 3/5/19 11:04 PM:
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{quote}I am not very clear about 'With in-progress edit log tailing enabled,
tooLongSinceLastLoad() will almost never return true resulting in edit logs not
rolled '. Can you describe it deeply?
{quote}
{{lastLoadTimeMs}} is updated when edit logs are successfully tailed from
active. With in-progress edit log tailing, every time the standby tails the
edit logs (every 60 seconds by default), this timestamp would be updated.
{{logRollPeriodMs}} by default is 120 seconds which means that the time since
{{lastLoadTimeMs}}
will never be greater than 120 seconds in normal circumstances. Hence
{{tooLongSinceLastLoad()}} will never return true in such a case.
was (Author: ekanth):
{quote}I am not very clear about 'With in-progress edit log tailing enabled,
tooLongSinceLastLoad() will almost never return true resulting in edit logs not
rolled '. Can you describe it deeply?{quote}
{lastLoadTimeMs} is updated when edit logs are successfully tailed from active.
With in-progress edit log tailing, every time the standby tails the edit logs
(every 60 seconds by default), this timestamp would be updated.
{logRollPeriodMs} by default is 120 seconds which means that the time since
{lastLoadTimeMs} will never be greater than 120 seconds in normal
circumstances. Hence, {tooLongSinceLastLoad()} will never return true in such a
case.
> Standby does not trigger edit log rolling when in-progress edit log tailing
> is enabled
> --------------------------------------------------------------------------------------
>
> Key: HDFS-14317
> URL: https://issues.apache.org/jira/browse/HDFS-14317
> Project: Hadoop HDFS
> Issue Type: Bug
> Affects Versions: 2.9.0, 3.0.0
> Reporter: Ekanth Sethuramalingam
> Assignee: Ekanth Sethuramalingam
> Priority: Critical
> Attachments: HDFS-14317.001.patch, HDFS-14317.002.patch,
> HDFS-14317.003.patch, HDFS-14317.004.patch
>
>
> The standby uses the following method to check if it is time to trigger edit
> log rolling on active.
> {code}
> /**
> * @return true if the configured log roll period has elapsed.
> */
> private boolean tooLongSinceLastLoad() {
> return logRollPeriodMs >= 0 &&
> (monotonicNow() - lastLoadTimeMs) > logRollPeriodMs ;
> }
> {code}
> In doTailEdits(), lastLoadTimeMs is updated when standby is able to
> successfully tail any edits
> {code}
> if (editsLoaded > 0) {
> lastLoadTimeMs = monotonicNow();
> }
> {code}
> The default configuration for {{dfs.ha.log-roll.period}} is 120 seconds and
> {{dfs.ha.tail-edits.period}} is 60 seconds. With in-progress edit log tailing
> enabled, tooLongSinceLastLoad() will almost never return true resulting in
> edit logs not rolled for a long time until this configuration
> {{dfs.namenode.edit.log.autoroll.multiplier.threshold}} takes effect.
> [In our deployment, this resulted in in-progress edit logs getting deleted.
> The sequence of events is that standby was able to checkpoint twice while the
> in-progress edit log was growing on active. When the
> NNStorageRetentionManager decided to cleanup old checkpoints and edit logs,
> it cleaned up the in-progress edit log from active and QJM (as the txnid on
> in-progress edit log was older than the 2 most recent checkpoints) resulting
> in irrecoverably losing a few minutes worth of metadata].
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