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https://issues.apache.org/jira/browse/HDFS-13511?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16496181#comment-16496181
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Xiao Chen commented on HDFS-13511:
----------------------------------
Thanks [[email protected]] for creating the jira, and [~gabor.bota] for
working on this.
Some comments:
- For downstream to use this, [compat
guideline|http://hadoop.apache.org/docs/r3.0.0/hadoop-project-dist/hadoop-common/Compatibility.html]
requires it to be public. Suggest to use Public + Unstable for the initial
version
- {{LocatedBlock}} is Private, let's not expose that via this exception. We
can just construct a string message on the fly, and do not cache the
LocatedBlock object. This way, we also don't have to worry about whether the
{{LocatedBlock}} is mutable or not. See {{ReplicaNotFoundException}} for
example.
> 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
> Assignee: Gabor Bota
> Priority: Major
> Attachments: HDFS-13511.001.patch
>
>
> 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 [[email protected]], 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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