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https://issues.apache.org/jira/browse/HDFS-15421?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17142713#comment-17142713
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Akira Ajisaka commented on HDFS-15421:
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Thank you [~kihwal] for the detailed report. I read your report and the
discussion in HDFS-14941.
In append operation, ANN first log {{OP_SET_GENSTAMP_V2}} and then log
{{OP_APPEND}}. After HDFS-14941, SNN rolls {{OP_SET_GENSTAMP_V2}} log and set
impending genstamp without updating the global genstamp. Next SNN rolls
{{OP_APPEND}} log but the global genstamp is not updated. That's why genstamp
is never updated and IBR always comes from the future. I think we need to
update genstamp when rolling {{OP_APPEND}}. In {{OP_TRUNCATE}}, it is the same.
> IBR leak causes standby NN to be stuck in safe mode
> ---------------------------------------------------
>
> Key: HDFS-15421
> URL: https://issues.apache.org/jira/browse/HDFS-15421
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: namenode
> Reporter: Kihwal Lee
> Priority: Blocker
>
> After HDFS-14941, update of the global gen stamp is delayed in certain
> situations. This makes the last set of incremental block reports from append
> "from future", which causes it to be simply re-queued to the pending DN
> message queue, rather than processed to complete the block. The last set of
> IBRs will leak and never cleaned until it transitions to active. The size of
> {{pendingDNMessages}} constantly grows until then.
> If a leak happens while in a startup safe mode, the namenode will never be
> able to come out of safe mode on its own.
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