Merge pull request #79723 from rachel-msft/edits614

Update concepts-read-replicas.md

Author: PRMerger16

articles/postgresql/concepts-read-replicas.md

@@ -5,7 +5,7 @@ author: rachel-msft
 ms.author: raagyema
 ms.service: postgresql
 ms.topic: conceptual
-ms.date: 06/05/2019
+ms.date: 06/14/2019
 ---
 
 # Read replicas in Azure Database for PostgreSQL - Single Server
@@ -118,6 +118,9 @@ PostgreSQL requires the value of the `max_connections` parameter on the read rep
 
 If you try to update the server values, but don't adhere to the limits, you receive an error.
 
+### max_prepared_transactions
+[PostgreSQL requires](https://www.postgresql.org/docs/10/hot-standby.html) the value of the `max_prepared_transactions` parameter on the read replica to be greater than or equal to the master value; otherwise, the replica won't start. If you want to change `max_prepared_transactions` on the master, first change it on the replicas.
+
 ### Stopped replicas
 If you stop replication between a master server and a read replica, the replica restarts to apply the change. The stopped replica becomes a standalone server that accepts both reads and writes. The standalone server can't be made into a replica again.