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https://issues.apache.org/jira/browse/HDFS-17593?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18090650#comment-18090650
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ASF GitHub Bot commented on HDFS-17593:
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boroknagyz opened a new pull request, #8561:
URL: https://github.com/apache/hadoop/pull/8561
Adds support for opening HDFS files with pre-fetched block locations,
eliminating redundant NameNode RPCs when callers already have cached block
metadata.
Changes:
- DFSClient.open() overload accepting LocatedBlocks
- DistributedFileSystem.openFileWithOptions() override that extracts
LocatedBlocks from HdfsLocatedFileStatus passed via withFileStatus()
- DistributedFileSystem.cloneDataInputStream() to create independent file
handles reusing block locations from an existing stream
- libhdfs hdfsCloneFile() C API for cloning file handles via JNI
- Integration tests verifying no NameNode RPC on clone/open with status
Contains content generated by Claude Opus 4.6
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### Description of PR
Adds support for opening HDFS files with pre-fetched block locations,
eliminating redundant NameNode RPCs when callers already have cached block
metadata.
### How was this patch tested?
Unit tests.
### For code changes:
- [x] Does the title or this PR starts with the corresponding JIRA issue id
(e.g. 'HADOOP-17799. Your PR title ...')?
- [ ] Object storage: have the integration tests been executed and the
endpoint declared according to the connector-specific documentation?
- [ ] If adding new dependencies to the code, are these dependencies
licensed in a way that is compatible for inclusion under [ASF
2.0](http://www.apache.org/legal/resolved.html#category-a)?
- [ ] If applicable, have you updated the `LICENSE`, `LICENSE-binary`,
`NOTICE-binary` files?
### AI Tooling
If an AI tool was used:
- [x] The PR includes the phrase "Contains content generated by <tool>"
where <tool> is the name of the AI tool used.
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> Allow setting block locations when opening streams
> --------------------------------------------------
>
> Key: HDFS-17593
> URL: https://issues.apache.org/jira/browse/HDFS-17593
> Project: Hadoop HDFS
> Issue Type: Improvement
> Reporter: Csaba Ringhofer
> Priority: Major
>
> The HDFS client seems to always get block locations from the namenode when
> opening a file:
> https://github.com/apache/hadoop/blob/4525c7e35ea22d7a6350b8af10eb8d2ff68376e7/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSClient.java#L1099
> This leads to unnecessary RPCs in Apache Impala when doing reads, as the
> block locations are cached globally and the executors already have a good
> guess about the block locations when opening a stream. Unless the cached
> block locations are stale ideally no RPC should be made to the namenode.
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