HA MT failover (#1234)

Author: as51340

pages/clustering/high-availability.mdx

@@ -446,9 +446,9 @@ about other REPLICAs to which it will replicate data. Once that request succeeds
 
 When failover is happening, some REPLICAs can also be down. From the list of alive REPLICAs, a new MAIN is chosen. First, the leader coordinator contacts each alive REPLICA
 to get info about each database's last commit timestamp. In the case of enabled multi-tenancy, from each instance coordinator will get info on all databases and their last commit
-timestamp. Currently, the coordinator chooses an instance to become a new MAIN by comparing the latest commit timestamp only of the default database for every instance. 
-If multiple instances have the same latest commit timestamp, the instance that was registered earlier will be chosen as a new MAIN. 
-
+timestamp. Currently, the coordinator chooses an instance to become a new MAIN by comparing the latest commit timestamps of all databases. The instance which is newest on most 
+databases is considered the best candidate for the new MAIN. If there are multiple instances which have the same number of newest databases, we sum timestamps of all databases
+and consider instance with a larger sum as the better candidate.
 
 ### Old MAIN rejoining to the cluster
 
@@ -874,4 +874,4 @@ that and automatically promote the first alive REPLICA to become the new MAIN. T
 
 </Steps>
 
-<CommunityLinks/>
+<CommunityLinks/>