Merge pull request #188626 from TheovanKraay/cassandra-mi-materialized-views

cassandra mi materialized views doc

Author: v-shils

articles/managed-instance-apache-cassandra/TOC.yml

@@ -51,6 +51,8 @@
       href: network-rules.md
     - name: Visualize metrics in Prometheus with Grafana
       href: visualize-prometheus-grafana.md
+    - name: Enable materialized views
+      href: materialized-views.md      
 - name: Reference
   items:
     - name: REST API

articles/managed-instance-apache-cassandra/materialized-views.md

@@ -0,0 +1,61 @@
+---
+title: Materialized views in Azure Managed Instance for Apache Cassandra
+description: Learn how to enable materialized views in Azure Managed Instance for Apache Cassandra.
+author: TheovanKraay
+ms.author: thvankra
+ms.service: managed-instance-apache-cassandra
+ms.topic: how-to
+ms.date: 02/15/2022
+---
+
+# Materialized views in Azure Managed Instance for Apache Cassandra
+
+Azure Managed Instance for Apache Cassandra provides automated deployment and scaling operations for managed open-source Apache Cassandra data centers. This article discusses how to enable materialized views. 
+
+## Materialized view support
+Materialized views are disabled by default, but users can enable them on their cluster. However, we discourage users of Azure Managed Instance for Apache Cassandra from using materialized views. They are experimental (see
+[Materialized Views marked experimental-Apache Mail Archives](https://lists.apache.org/thread/o5bk8xyxyl6k3sjf7kkblqw52gm5s9mp) and the [proposal to do so](https://www.mail-archive.com/[email protected]/msg11516.html)). In particular:
+
+- The implementation of materialized views is distributed system design that
+  hasn’t been extensively modeled and simulated. There have been no formal
+  proofs about its properties.
+- There is no way to determine if a materialized view is out of sync with its
+  base table.
+- There is no upper bound on how long it takes for a materialized view to be
+  synced when there is a change to its base table.
+- If there is an error and a materialized view goes out of sync, the only way to
+  repair it is to drop the materialized view and recreate it. 
+
+Microsoft cannot offer any SLA or support on issues with materialized views.
+
+## Alternatives to materialized views
+Like most NoSQL stores, Apache Cassandra is not designed to have a normalized data model. If you need to update data in more than one place, your program should send all the necessary statements as part of a [BATCH](https://cassandra.apache.org/doc/trunk/cassandra/cql/dml.html#batch_statement). This has two advantages over materialized views:
+
+- BATCH guarantees that all statements in the batch are committed or none.
+- All the statements have the same quorum and commit semantics.
+
+If your workload truly needs a normalized data model, consider a scalable relational store like Azure's [Hyperscale PostgreSQL](/azure/postgresql/hyperscale/).
+
+## How to enable materialized views
+You need to set `enable_materialized_views: true` in the `rawUserConfig` field of your Cassandra data center. To do so, use the following Azure CLI command to update each data center in your cluster:
+
+```azurecli-interactive
+FRAGMENT="enable_materialized_views: true"
+ENCODED_FRAGMENT=$(echo "$FRAGMENT" | base64 -w 0)
+# or
+# ENCODED_FRAGMENT="ZW5hYmxlX21hdGVyaWFsaXplZF92aWV3czogdHJ1ZQo="
+resourceGroupName='MyResourceGroup'
+clusterName='cassandra-hybrid-cluster'
+dataCenterName='dc1'
+az managed-cassandra datacenter update \
+    --resource-group $resourceGroupName \
+	--cluster-name $clusterName \
+	--data-center-name $dataCenterName \
+	--base64-encoded-cassandra-yaml-fragment "$ENCODED_FRAGMENT"
+```
+
+## Next steps
+
+* [Create a managed instance cluster from the Azure portal](create-cluster-portal.md)
+* [Deploy a Managed Apache Spark Cluster with Azure Databricks](deploy-cluster-databricks.md)
+* [Manage Azure Managed Instance for Apache Cassandra resources using Azure CLI](manage-resources-cli.md)