[jira] [Created] (HDFS-13511) Provide specialized exception when block length cannot be obtained

["Ted Yu (JIRA)" <ji...@apache.org>]

Ted Yu created HDFS-13511:
-----------------------------

             Summary: Provide specialized exception when block length cannot be obtained
                 Key: HDFS-13511
                 URL: https://issues.apache.org/jira/browse/HDFS-13511
             Project: Hadoop HDFS
          Issue Type: Improvement
            Reporter: Ted Yu


In downstream project, I saw the following code:
{code}
        FSDataInputStream inputStream = hdfs.open(new Path(path));
...
        if (options.getRecoverFailedOpen() && dfs != null && e.getMessage().toLowerCase()
            .startsWith("cannot obtain block length for")) {
{code}
The above tightly depends on the following in DFSInputStream#readBlockLength
{code}
    throw new IOException("Cannot obtain block length for " + locatedblock);
{code}
The check based on string matching is brittle in production deployment.

After discussing with [~stevel@apache.org], better approach is to introduce specialized IOException, e.g. CannotObtainBlockLengthException so that downstream project doesn't have to rely on string matching.



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