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https://issues.apache.org/jira/browse/HDFS-17920?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18081432#comment-18081432
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ASF GitHub Bot commented on HDFS-17920:
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boky01 opened a new pull request, #8502:
URL: https://github.com/apache/hadoop/pull/8502
### Description of PR
The test TestDiskError.testShutdown can enter an infinite loop if
dn.isDatanodeUp() fails to evaluate to true. Because there is no explicit
timeout configured for this loop, it runs indefinitely. Inside the loop, the
file creation, replication, and deletion operations execute incredibly fast. If
the loop runs uninterrupted, it generates a massive volume of log entries in a
short period. Consequently, if the exit condition is never met, the test will
continuously write to the logs until the host storage runs completely out of
space, which is ultimately what crashes the test execution.
> TestDiskError.testShutdown can run into infinite loop
> -----------------------------------------------------
>
> Key: HDFS-17920
> URL: https://issues.apache.org/jira/browse/HDFS-17920
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: datanode
> Reporter: András Bokor
> Priority: Critical
>
> The test case tests if DN shuts down when there is a disk failure (that is
> simulated by the test).
> We found that when this feature does not work for whatever reason
> TestDiskError.testShutdown takes a long time and did not finish, also it
> consumes all the storage space. The log file is somewhere around 11 GB, but
> it can be increased by increasing the container size.
> Since the log file is huge and capable of running indefinitely, it is
> suspicious that there might be an infinite loop somewhere in the test.
> I checked what loops exist [in the test
> file;|https://github.com/apache/hadoop/blob/734dd8a67cd6df56b59ff75aa43de57834a0d248/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestDiskError.java#L121]
> there aren't many, and with one exception, they all run only a few
> iterations:
> {code:java}
> DataNode dn = cluster.getDataNodes().get(dnIndex);
> for (int i=0; dn.isDatanodeUp(); i++) {
> Path fileName = new Path("/test.txt"+i);
> DFSTestUtil.createFile(fs, fileName, 1024, (short)2, 1L);
> DFSTestUtil.waitReplication(fs, fileName, (short)2);
> fs.delete(fileName, true);
> } {code}
> Here, we keep creating and deleting new files until the DataNode (DN) dies. I
> don't know how long the replication takes, but based on the file size and the
> replication factor of 2, it should happen quickly. This is a suspicious
> section because if the test doesn't finish quickly (meaning the "bad" DN
> doesn't shut itself down), it’s conceivable that a vast number of file
> operations are generating a massive amount of logs.I ran a grep on the log
> file to see how many iterations are executed, and I found a line like this:
>
> {code:java}
> BLOCK* allocate blk_1073970157_229333, replicas=127.0.0.1:34219,
> 127.0.0.1:39923 for /test.txt114166{code}
>
> This indicates that this single unit test case generates over a hundred
> thousand file operations on its own. Based on the log I examined, which
> covers a half-hour window, the loop is running about 60 times per second; I'm
> not even sure if this makes sense.
> Introducing some kind of interval plus a timeout would likely help, as the
> test currently works in a way where if the feature under test fails, you
> don't get an assertion error—you get an infinite loop.
> *Please note that* {*}we are not addressing the root cause of the possible
> shutdown failure{*}; instead, we are targeting the resulting infinite loop
> and the unnecessarily large log file.
> Also, I have set the priority to Critical (even though a unit test failure
> does not indicate that) because, this issue can block CI process.
>
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