[jira] [Resolved] (HDFS-17920) TestDiskError.testShutdown can run into infinite loop

["Attila Doroszlai (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HDFS-17920?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Attila Doroszlai resolved HDFS-17920.
-------------------------------------
    Fix Version/s: 3.6.0
       Resolution: Fixed

> 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
>            Assignee: András Bokor
>            Priority: Critical
>              Labels: pull-request-available
>             Fix For: 3.6.0
>
>
> 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 issue does not indicate that) because, allowing a test to loop indefinitely and exhaust host storage poses a severe operational risk. It triggers OS-level instability, corrupts local application caches/databases, and acts as a *CI/CD Blocker* by causing hard disk failures on shared build agents, ultimately disrupting the entire engineering pipeline.
>  



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