[jira] [Updated] (HDFS-15443) Setting dfs.datanode.max.transfer.threads to a very small value can cause strange failure.

["Stephen O'Donnell (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HDFS-15443?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Stephen O'Donnell updated HDFS-15443:
-------------------------------------
    Fix Version/s: 3.3.1

> Setting dfs.datanode.max.transfer.threads to a very small value can cause strange failure.
> ------------------------------------------------------------------------------------------
>
>                 Key: HDFS-15443
>                 URL: https://issues.apache.org/jira/browse/HDFS-15443
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: datanode
>            Reporter: AMC-team
>            Assignee: AMC-team
>            Priority: Major
>             Fix For: 3.3.1, 3.4.0
>
>         Attachments: HDFS-15443.000.patch, HDFS-15443.001.patch, HDFS-15443.002.patch, HDFS-15443.003.patch
>
>
> Configuration parameter dfs.datanode.max.transfer.threads is to specify the maximum number of threads to use for transferring data in and out of the DN. This is a vital param that need to tune carefully. 
> {code:java}
> // DataXceiverServer.java
> // Make sure the xceiver count is not exceeded
> intcurXceiverCount = datanode.getXceiverCount();
> if (curXceiverCount > maxXceiverCount) {
> thrownewIOException("Xceiver count " + curXceiverCount
> + " exceeds the limit of concurrent xceivers: "
> + maxXceiverCount);
> }
> {code}
> There are many issues that caused by not setting this param to an appropriate value. However, there is no any check code to restrict the parameter. Although having a hard-and-fast rule is difficult because we need to consider number of cores, main memory etc, *we can prevent users from setting this value to an absolute wrong value by accident.* (e.g. a negative value that totally break the availability of datanode.)
> *How to fix:*
> Add proper check code for the parameter.



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