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https://issues.apache.org/jira/browse/HADOOP-18246?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17630739#comment-17630739
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ASF GitHub Bot commented on HADOOP-18246:
-----------------------------------------
ahmarsuhail commented on code in PR #5120:
URL: https://github.com/apache/hadoop/pull/5120#discussion_r1017404868
##########
hadoop-tools/hadoop-aws/src/site/markdown/tools/hadoop-aws/prefetching.md:
##########
@@ -43,6 +43,12 @@ Multiple blocks may be read in parallel.
|`fs.s3a.prefetch.block.size` |Size of a block |`8M` |
|`fs.s3a.prefetch.block.count` |Number of blocks to prefetch |`8` |
+Although, default size of the block for prefetching the input stream is 8 MB,
+minimum size allowed to set is 1 byte for a block.
+User should set the block size with the understanding that smaller block sizes
increases the number of blocks.
+Thus, smaller block size affects the performance by increasing the overhead
for reading and prefetching
+each block.
Review Comment:
```suggestion
The default size of a block is 8MB, and the minimum allowed block size is 1
byte.
Decreasing block size will increase the number of blocks to be read for a
file.
A smaller block size may negatively impact performance as the number of
prefetches required will increase.
```
> Remove lower limit on s3a prefetching/caching block size
> --------------------------------------------------------
>
> Key: HADOOP-18246
> URL: https://issues.apache.org/jira/browse/HADOOP-18246
> Project: Hadoop Common
> Issue Type: Sub-task
> Affects Versions: 3.4.0
> Reporter: Daniel Carl Jones
> Assignee: Ankit Saurabh
> Priority: Minor
> Labels: pull-request-available
>
> The minimum allowed block size currently is {{PREFETCH_BLOCK_DEFAULT_SIZE}}
> (8MB).
> {code:java}
> this.prefetchBlockSize = intOption(
> conf, PREFETCH_BLOCK_SIZE_KEY,
> PREFETCH_BLOCK_DEFAULT_SIZE, PREFETCH_BLOCK_DEFAULT_SIZE);{code}
> [https://github.com/apache/hadoop/blob/3aa03e0eb95bbcb066144706e06509f0e0549196/hadoop-tools/hadoop-aws/src/main/java/org/apache/hadoop/fs/s3a/S3AFileSystem.java#L487-L488]
> Why is this the case and should we lower or remove it?
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