CHANGELOG.md in statsd-instrument-3.9.0 vs CHANGELOG.md in statsd-instrument-3.9.1

@@ -4,19 +4,25 @@
 creating a pull request, please add an entry to the "unreleased changes"
 section below.
 
 ## Unreleased changes
 
+## Version 3.9.1
+
+- [#378](https://github.com/Shopify/statsd-instrument/pull/378) - Respect sampling rate when aggregation is enabled, just for timing metrics.
+  Not respecting sampling rate, incurs in a performance penalty, as we will send more metrics than expected.
+  Moreover, it overloads the StatsD server, which has to send out and process more metrics than expected.
+
 ## Version 3.9.0
 
 - Introduced an experimental aggregation feature to improve the efficiency of metrics reporting by aggregating 
 multiple metric events into a single sample. This reduces the number of network requests and can significantly 
 decrease the overhead associated with high-frequency metric reporting. To enable metric aggregation, set the 
 `STATSD_ENABLE_AGGREGATION` environment variable to true. More information on this feature is available in the README.
 - Added support for sending StatsD via Unix domain sockets. This feature is enabled by
 setting the `STATSD_SOCKET` environment variable to the path of the Unix domain socket.
   - :warning: **Possible breaking change**: We removed/renamed some classes and now Sinks are generic, so the classes `UDPSink` and `UDPBatchedSink` are now called
-`StatsD::Instrument::Sink` and `StatsD::Instrument::Sink` respectively.
+`StatsD::Instrument::Sink` and `StatsD::Instrument::BatchedSink` respectively.
 If you used those internal classes, you will need to update your code to use the new classes.
 
 ## Version 3.8.0
 
 - UDP batching will now track statistics about its own batching performance, and