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https://issues.apache.org/jira/browse/HADOOP-18378?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17611111#comment-17611111
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ASF GitHub Bot commented on HADOOP-18378:
-----------------------------------------
passaro opened a new pull request, #4955:
URL: https://github.com/apache/hadoop/pull/4955
### Description of PR
[HADOOP-18378](https://issues.apache.org/jira/browse/HADOOP-18378). Make
S3APrefetchingInputStream.seek() completely lazy. Calls to seek() will not
affect the current buffer nor interfere with prefetching, until read() is
called. This change allows various usage patterns to benefit from prefetching,
e.g. when calling readFully(position, buffer) in a loop for contiguous
positions, the intermediate internal calls to seek() will be noops and
prefetching will have the same performance as in a sequential read.
### How was this patch tested?
Tested with `mvn clean verify` on a bucket in `eu-west-2`.
### For code changes:
- [x] Does the title or this PR starts with the corresponding JIRA issue id
(e.g. 'HADOOP-17799. Your PR title ...')?
- [x] 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?
> Implement readFully(long position, byte[] buffer, int offset, int length)
> -------------------------------------------------------------------------
>
> Key: HADOOP-18378
> URL: https://issues.apache.org/jira/browse/HADOOP-18378
> Project: Hadoop Common
> Issue Type: Sub-task
> Components: fs/s3
> Affects Versions: 3.4.0
> Reporter: Ahmar Suhail
> Assignee: Alessandro Passaro
> Priority: Minor
>
> Implement readFully(long position, byte[] buffer, int offset, int length) in
> PrefetchingInputStream, as it currently uses FSInputStream's
> [readFully|https://github.com/apache/hadoop/blob/trunk/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/FSInputStream.java#L136]
> which calls read(long position, byte[] buffer, int offset, int length).
> This read then seeks to the position (which is ok), but then seeks back to
> the original starting position at the end (so always seeking back to 0). this
> is pretty bad for the prefetching implementation as it means lots of caching
> to disk and getting blocks from disk.
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