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https://issues.apache.org/jira/browse/HDFS-14305?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16777091#comment-16777091
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He Xiaoqiao commented on HDFS-14305:
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Thanks [~xkrogen]. I will update code style and add some comment later.
{quote}I think 10 bits for the mask seems a little high to me; I agree with
Chao that I can't think of a situation where you would need more than 32 or 64,
and fewer bits for the per-NN key space mean a higher chance of collision on a
NameNode restart.{quote}
Considering that there are total 32 bits of Integer and it is enough for
rolling serial no using 22 bits. another side, fewer bits for mask more
namenodes it could cover that avoid collision. So I choose 10 bits.
Of course, it is OK for me if choose number of mask bits between 3~10. Thanks
again.
> Serial number in BlockTokenSecretManager could overlap between different
> namenodes
> ----------------------------------------------------------------------------------
>
> Key: HDFS-14305
> URL: https://issues.apache.org/jira/browse/HDFS-14305
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: security
> Reporter: Chao Sun
> Assignee: Chao Sun
> Priority: Major
> Attachments: HDFS-14305.001.patch, HDFS-14305.002.patch,
> HDFS-14305.003.patch
>
>
> Currently, a {{BlockTokenSecretManager}} starts with a random integer as the
> initial serial number, and then use this formula to rotate it:
> {code:java}
> this.intRange = Integer.MAX_VALUE / numNNs;
> this.nnRangeStart = intRange * nnIndex;
> this.serialNo = (this.serialNo % intRange) + (nnRangeStart);
> {code}
> while {{numNNs}} is the total number of NameNodes in the cluster, and
> {{nnIndex}} is the index of the current NameNode specified in the
> configuration {{dfs.ha.namenodes.<nameservice>}}.
> However, with this approach, different NameNode could have overlapping ranges
> for serial number. For simplicity, let's assume {{Integer.MAX_VALUE}} is 100,
> and we have 2 NameNodes {{nn1}} and {{nn2}} in configuration. Then the ranges
> for these two are:
> {code}
> nn1 -> [-49, 49]
> nn2 -> [1, 99]
> {code}
> This is because the initial serial number could be any negative integer.
> Moreover, when the keys are updated, the serial number will again be updated
> with the formula:
> {code}
> this.serialNo = (this.serialNo % intRange) + (nnRangeStart);
> {code}
> which means the new serial number could be updated to a range that belongs to
> a different NameNode, thus increasing the chance of collision again.
> When the collision happens, DataNodes could overwrite an existing key which
> will cause clients to fail because of {{InvalidToken}} error.
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