# Amazon EMR 7.4.0 - Hadoop release notes
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## Amazon EMR 7.4.0 - Hadoop changes
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| Type | Description | 
| --- | --- | 
| Upgrade | Hadoop version is upgraded to 3.4.0, refer to [OSS release notes](https://hadoop.apache.org/docs/r3.4.0/hadoop-project-dist/hadoop-common/release/3.4.0/RELEASENOTES.3.4.0.html). | 
| Bug Fix | Fix negative Pending and Allocated Yarn metrics for FairScheduler | 
| Bug Fix | [YARN-11702 ](https://issues.apache.org/jira/browse/YARN-11702): Fix Yarn over allocating containers | 
| Bug Fix | Improve race-condition handling when downscaling nodes  | 
| Improvement | [HADOOP-18679 ](https://issues.apache.org/jira/browse/HADOOP-18679): Add API for bulk/paged delete of files  | 
| Improvement | [HADOOP-19203](https://issues.apache.org/jira/browse/HADOOP-19203): WrappedIO BulkDelete API to raise IOEs as UncheckedIOExceptions | 
| Improvement | [HADOOP-19205](https://issues.apache.org/jira/browse/HADOOP-19205): S3A: initialization/close slower than with v1 SDK  | 
| Improvement | [HADOOP-19161](https://issues.apache.org/jira/browse/HADOOP-19205): S3A: option *fs.s3a.performance.flags* to take list of performance flags | 
| Improvement | [HADOOP-19072](https://issues.apache.org/jira/browse/HADOOP-19205): S3A: expand optimisations on stores with *fs.s3a.performance.flags* for mkdir | 

## Amazon EMR 7.4.0 - Hadoop features
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See the following list for new Hadoop features in Amazon EMR 7.4.0.
+ The default configuration values have been fine-tuned for optimal performance: 
  + **mapreduce.input.fileinputformat.list-status.num-threads=10** – This is up from 1.
  + **fs.s3a.block.size=64M** – This is up from 32M.
  + **fs.s3a.multipart.size=128M** – This is up from 64M.
+ Out-of-the-box performance enhancing optimizations for accelerating MapReduce jobs with the S3A filesystem.