Add support for deletes in the memberlist backed KV store

CHANGELOG.md

@@ -236,6 +236,7 @@
 * [ENHANCEMENT] Cache: Add `.Advance()` methods to mock cache clients for easier testing of TTLs. #601
 * [ENHANCEMENT] Memberlist: Add concurrency to the transport's WriteTo method. #525
 * [ENHANCEMENT] Memberlist: Notifications can now be processed once per interval specified by `-memberlist.notify-interval` to reduce notify storms in large clusters. #592
+* [ENHANCEMENT] Memberlist: Implemented the `Delete` operation in the memberlist backed KV store. How frequently deleted entries are cleaned up is specified by the `-memberlist.obsolete-entries-timeout` flag. #612
 * [BUGFIX] spanlogger: Support multiple tenant IDs. #59
 * [BUGFIX] Memberlist: fixed corrupted packets when sending compound messages with more than 255 messages or messages bigger than 64KB. #85
 * [BUGFIX] Ring: `ring_member_ownership_percent` and `ring_tokens_owned` metrics are not updated on scale down. #109

kv/memberlist/kv.proto

@@ -19,4 +19,9 @@ message KeyValuePair {
 
     // ID of the codec used to write the value
     string codec = 3;
+
+    // Is this Key marked for deletion?
+    bool deleted = 4;
+    // When was the key last updated?
+    int64 update_time_millis = 5;
 }