CHANGELOG: update changelogs for backport of PR #10646

CHANGELOG-3.1.md

@@ -14,6 +14,10 @@ The [minimum recommended etcd versions to run in **production**](https://groups.
 
 - [Strip out insecure endpoints from DNS SRV records when using discovery](https://github.com/etcd-io/etcd/pull/10443) with etcdctl v2
 
+### Metrics, Monitoring
+
+- Fix bug where [db_compaction_total_duration_milliseconds metric incorrectly measured duration as 0](https://github.com/etcd-io/etcd/pull/10646).
+
 <hr>
 
 ## [v3.1.20](https://github.com/etcd-io/etcd/releases/tag/v3.1.20) (2018-10-10)

CHANGELOG-3.2.md

@@ -15,6 +15,10 @@ The [minimum recommended etcd versions to run in **production**](https://groups.
 
 - [Strip out insecure endpoints from DNS SRV records when using discovery](https://github.com/etcd-io/etcd/pull/10443) with etcdctl v2
 
+### Metrics, Monitoring
+
+- Fix bug where [db_compaction_total_duration_milliseconds metric incorrectly measured duration as 0](https://github.com/etcd-io/etcd/pull/10646).
+
 <hr>
 
 

CHANGELOG-3.3.md

@@ -21,6 +21,9 @@ See [code changes](https://github.com/etcd-io/etcd/compare/v3.3.11...v3.3.12) an
 
 - Compile with [*Go 1.10.8*](https://golang.org/doc/devel/release.html#go1.10).
 
+### Metrics, Monitoring
+
+- Fix bug where [db_compaction_total_duration_milliseconds metric incorrectly measured duration as 0](https://github.com/etcd-io/etcd/pull/10646).
 
 <hr>