steveloughran opened a new pull request, #5859:
URL: https://github.com/apache/hadoop/pull/5859
This change has all of PR #5689 *except* for changing the default value of
marker retention from keep to delete.
1. leaves the default value of fs.s3a.directory.marker.retention at "delete"
2. no longer prints a message when an S3A FS instances is instantiated with
any option other than delete.
3. Updates the directory marker documentation
Switching to marker retention improves performance on any S3 bucket as there
are no needless marker DELETE requests -leading to a reduction in write IOPS
and and any delays waiting for the DELETE call to finish.
There are *very* significant improvements on versioned buckets, where
tombstone markers slow down LIST operations: the more tombstones there are, the
worse query planning gets.
Having versioning enabled on production stores is the foundation of any data
protection strategy, so this has tangible benefits in production.
Marker deletion is *not* compatible with older hadoop releases; specifically
- Hadoop branch 2 < 2.10.2
- Any release of Hadoop 3.0.x and Hadoop 3.1.x
- Hadoop 3.2.0 and 3.2.1
- Hadoop 3.3.0 Incompatible releases have no problems reading data in stores
where markers are retained, but can get confused when deleting or renaming
directories.
Contributed by Steve Loughran
Change-Id: Ic9a05357a4b1b1ff6dfecf8b0f30e1eeedb2fe75
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