Add cluster limitations

3.5/http/transaction-stream-transaction.md

@@ -66,3 +66,13 @@ until the entire transaction times out.
 List currently ongoing Transactions
 -----------------------------------
 {% docublock get_api_transactions %}
+
+Cluster Limitations
+---------------------
+
+A maximum lifetime and transaction size for stream transactions is enforced
+on the coordinator to ensure that transactions cannot block the cluster from
+operating properly:
+
+- Maximum lifetime of 60 seconds
+- Maximum size of 128 MB