Backport of (DOCSP-35060) Perf considerations for multi regions for OM and AppDB (#81) to v7.0 (#82)

Backport of (#81)

https://jira.mongodb.org/browse/DOCSP-35060


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Author: JuliaMongo

source/tutorial/configure-application-high-availability.txt

@@ -202,6 +202,47 @@ Your |onprem| instance stays in **Upgrade Mode** until all |onprem|
 hosts have been upgraded and restarted. You should not upgrade more
 than one |onprem| host at a time.
 
+.. _opsmgr-multi-regional-perf-considerations:
+
+Performance in Multi-Region Deployments
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The geographical distribution of the Application Database and |onprem|
+instances might impact the performance of the |application|.
+
+Multi-region Application Database Performance
++++++++++++++++++++++++++++++++++++++++++++++++
+
+If you plan to replicate the Application Database across multiple regions,
+consider that many of the |onprem| write workload operations use
+``w:2`` :manual:`write concern </reference/write-concern>`, which requires
+acknowledgement from the primary member and one secondary member of the
+replica set for each write operation.
+
+Therefore, having a secondary replica member of the Application Database in
+the **same** region as the primary member can lead to better read and write
+performance.
+
+For example, deploying three Application Database replica set members in
+three regions in a 1-1-1 fashion might result in worse performance
+compared with deploying three Application Database replica members in
+two regions in a 2-1 fashion, where one region hosts two Application Database
+replica set members and another region hosts the third replica set member.
+
+Performance of the |mms| UI
++++++++++++++++++++++++++++++++++++
+
+The |mms| UI is more performant if you connect to the |application| instance
+deployed it in the same region as the Application Database primary member
+of the Application Database replica set.
+
+In other words, you may achieve a better user experience connecting to
+the |application| instance hosted in the same region as the
+Application Database primary member of the replica set, rather than
+connecting to a closer |application| instance where the instance itself
+must connect to a primary Application Database replica set member hosted in
+a different, distant region with a high latency.
+
 Prerequisites
 -------------