[HDFS-13511] Provide specialized exception when block length cannot be obtained

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 3.2.0, 3.1.1, 2.9.3, 2.10.1
• Hadoop Flags: Reviewed
• Assignee: Gabor Bota
• Reporter: Ted Yu
• Created: 27/Apr/18 15:38
• Updated: 12/Dec/19 11:25
• Resolved: 06/Jun/18 04:25

Description

In downstream project, I saw the following code:

        FSDataInputStream inputStream = hdfs.open(new Path(path));
...
        if (options.getRecoverFailedOpen() && dfs != null && e.getMessage().toLowerCase()
            .startsWith("cannot obtain block length for")) {

The above tightly depends on the following in DFSInputStream#readBlockLength

    throw new IOException("Cannot obtain block length for " + locatedblock);

The check based on string matching is brittle in production deployment.

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

Issue Links

• is related to: HDFS-11711 DN should not delete the block On "Too many open files" Exception