milleruntime commented on a change in pull request #261:
URL: https://github.com/apache/accumulo-website/pull/261#discussion_r567904923
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File path: _posts/release/2020-01-19-accumulo-2.1.0.md
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@@ -7,12 +7,50 @@ draft: true
## Notable Changes
+### Compaction Changes
+
+Significant changes were made to how Accumulo compacts files in this release.
See
+{% dlink administration/compaction %} for details, below are some highlights.
+
+ * Multiple concurrent compactions per tablet on disjoint files is now
+ supported. Previously only a single compaction could run on a tablet. This
+ allows tablets that are running long compactions on large files to
+ concurrently compact new smaller files that arrive.
+ * Multiple compaction thread pools per tablet server are now supported.
+ Previously only a single thread pool existed within a tablet server for
+ compactions. With a single thread pool, if all threads are working on long
+ compactions it can starve quick compactions. Now compactions with little
+ data can be processed by dedicated thread pools.
+ * Accumulo's default algorithm for selecting files to compact was modified to
+ select the smallest set of files that meet the compaction ratio criteria
+ instead of the largest set. This change makes tablets more aggressive about
+ reducing their number files while still doing logarithmic compaction work.
+ This change also enables efficiently compacting new small files that arrive
+ during a long running compaction.
+ * Having dedicated compaction threads pools for tables is now supported
+ through configuration. The default configuration for Accumulo sets up
+ dedicated thread pools for compacting the Accumulo metadata table.
+ * Merging minor compactions were dropped. These were added to Accumulo to
+ address the problem of new files arriving while a long running compaction
+ was running. Merging minor compactions could cause O(N^2) compaction work.
+ The new compaction changes in this release can satisfy this use case while
+ doing a logarithmic amount of work.
+
+Accumulo has a pluggable user interface called CompactionStrategy, it was
+deprecated in this release and replaced with new interfaces in the public API.
+The javadocs for CompactionStrategy have more detailed information about its
+deprecation. CompactionStrategy transitively referenced many Accumulo types
+that are not public API. Therefore it is extremely difficult to know if
+compactions strategies written for one release of Accumulo will work with a
+later release. The new interfaces that replace CompactionStrategy only use
+public API types making it easier to write code that works across releases.
Review comment:
The last paragraph could be shorter. It could just say:
```suggestion
"The CompactionStrategy interface was deprecated in favor of new interfaces
in the public
API. The javadocs for CompactionStrategy have more detailed information
about its deprecation.
```
If the javadoc already includes the deprecation justification, just include
a link to the javadoc.
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