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https://issues.apache.org/jira/browse/HDFS-13609?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17277250#comment-17277250
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Erik Krogen commented on HDFS-13609:
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Hi [~xuzq_zander], thanks for taking a look.
{quote}
when onlyDurableTxns is false, maxAllowedTxns = responseCounts.get(0)
{quote}
Correct me if I'm wrong but I think you have this backwards. If
{{onlyDurableTxns}} is false, then {{maxAllowedTxns = highestTxnCount}} which
is {{responseCounts.get(2)}}
It is when {{onlyDurableTxns}} is true that you get {{responseCounts.get(0)}}.
In this case, we really do need to take the lowest of the returned values.
Since we only got 3 responses, we can't make any assumptions about the other 2
JNs, so just assume they have 0 txns. We only want to take txns that have
landed on a quorum of JNs (thus becoming durable). Thus since we only got 3
responses, we have to take the lowest txn that any of those responses are aware
of. For example if we got back {{(5, 10, 20)}}, then only txns 1-5 are
available on all 3 JNs we got responses from, so those are the only
transactions we know are durable. Of course more _might_ be durable if they
were persisted on the two JNs we didn't get responses from, but we don't know
that.
Let me know if that clears things up.
> [Edit Tail Fast Path Pt 3] NameNode-side changes to support tailing edits via
> RPC
> ---------------------------------------------------------------------------------
>
> Key: HDFS-13609
> URL: https://issues.apache.org/jira/browse/HDFS-13609
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: ha, namenode
> Reporter: Erik Krogen
> Assignee: Erik Krogen
> Priority: Major
> Fix For: HDFS-12943, 3.3.0
>
> Attachments: HDFS-13609-HDFS-12943.000.patch,
> HDFS-13609-HDFS-12943.001.patch, HDFS-13609-HDFS-12943.002.patch,
> HDFS-13609-HDFS-12943.003.patch, HDFS-13609-HDFS-12943.004.patch
>
>
> See HDFS-13150 for the full design.
> This JIRA is targetted at the NameNode-side changes to enable tailing
> in-progress edits via the RPC mechanism added in HDFS-13608. Most changes are
> in the QuorumJournalManager.
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