Add flag to disable materialized views, and warnings on creation

Patch by Blake Eggleston; Reviewed by Aleksey Yeschenko for CASSANDRA-13959

CHANGES.txt

@@ -1,10 +1,10 @@
 3.0.16
+ * Add flag to disable materialized views, and warnings on creation (CASSANDRA-13959)
  * Don't let user drop or generally break tables in system_distributed (CASSANDRA-13813)
  * Provide a JMX call to sync schema with local storage (CASSANDRA-13954)
  * Mishandling of cells for removed/dropped columns when reading legacy files (CASSANDRA-13939)
  * Deserialise sstable metadata in nodetool verify (CASSANDRA-13922)
 
-
 3.0.15
  * Improve TRUNCATE performance (CASSANDRA-13909)
  * Implement short read protection on partition boundaries (CASSANDRA-13595)

NEWS.txt

@@ -21,6 +21,14 @@ Upgrading
    - Nothing specific to this release, but please see previous upgrading sections,
      especially if you are upgrading from 2.2.
 
+Materialized Views
+-------------------
+   - Following a discussion regarding concerns about the design and safety of Materialized Views, the C* development
+     community no longer recommends them for production use, and considers them experimental. Warnings messages will
+     now be logged when they are created. (See https://www.mail-archive.com/dev@cassandra.apache.org/msg11511.html)
+   - An 'enable_materialized_views' flag has been added to cassandra.yaml to allow operators to prevent creation of
+     views
+
 3.0.15
 =====
 

conf/cassandra.yaml

@@ -952,6 +952,10 @@ enable_user_defined_functions: false
 # This option has no effect, if enable_user_defined_functions is false.
 enable_scripted_user_defined_functions: false
 
+# Enables materialized view creation on this node.
+# Materialized views are considered experimental and are not recommended for production use.
+enable_materialized_views: true
+
 # The default Windows kernel timer and scheduling resolution is 15.6ms for power conservation.
 # Lowering this value on Windows can provide much tighter latency and better throughput, however
 # some virtualized environments may see a negative performance impact from changing this setting

src/java/org/apache/cassandra/config/Config.java

@@ -308,6 +308,9 @@ public class Config
 
     public boolean enable_user_defined_functions = false;
     public boolean enable_scripted_user_defined_functions = false;
+
+    public boolean enable_materialized_views = true;
+
     /**
      * Optionally disable asynchronous UDF execution.
      * Disabling asynchronous UDF execution also implicitly disables the security-manager!

src/java/org/apache/cassandra/config/DatabaseDescriptor.java

@@ -2043,6 +2043,11 @@ public class DatabaseDescriptor
         conf.user_defined_function_warn_timeout = userDefinedFunctionWarnTimeout;
     }
 
+    public static boolean enableMaterializedViews()
+    {
+        return conf.enable_materialized_views;
+    }
+
     public static long getUserDefinedFunctionFailTimeout()
     {
         return conf.user_defined_function_fail_timeout;

src/java/org/apache/cassandra/cql3/statements/CreateViewStatement.java

@@ -23,9 +23,13 @@ import java.util.stream.Collectors;
 
 import com.google.common.collect.Iterables;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 import org.apache.cassandra.auth.Permission;
 import org.apache.cassandra.config.CFMetaData;
 import org.apache.cassandra.config.ColumnDefinition;
+import org.apache.cassandra.config.DatabaseDescriptor;
 import org.apache.cassandra.config.Schema;
 import org.apache.cassandra.config.ViewDefinition;
 import org.apache.cassandra.cql3.*;
@@ -49,6 +53,8 @@ import org.apache.cassandra.transport.Event;
 
 public class CreateViewStatement extends SchemaAlteringStatement
 {
+    private static final Logger logger = LoggerFactory.getLogger(CreateViewStatement.class);
+
     private final CFName baseName;
     private final List<RawSelector> selectClause;
     private final WhereClause whereClause;
@@ -114,6 +120,11 @@ public class CreateViewStatement extends SchemaAlteringStatement
 
     public Event.SchemaChange announceMigration(QueryState queryState, boolean isLocalOnly) throws RequestValidationException
     {
+        if (!DatabaseDescriptor.enableMaterializedViews())
+        {
+            throw new InvalidRequestException("Materialized views are disabled. Enable in cassandra.yaml to use.");
+        }
+
         // We need to make sure that:
         //  - primary key includes all columns in base table's primary key
         //  - make sure that the select statement does not have anything other than columns
@@ -303,8 +314,13 @@ public class CreateViewStatement extends SchemaAlteringStatement
                                                        whereClauseText,
                                                        viewCfm);
 
+        logger.warn("Creating materialized view {} for {}.{}. " +
+                    "Materialized views are experimental and are not recommended for production use.",
+                    definition.viewName, cfm.ksName, cfm.cfName);
+
         try
         {
+            ClientWarn.instance.warn("Materialized views are experimental and are not recommended for production use.");
             MigrationManager.announceNewView(definition, isLocalOnly);
             return new Event.SchemaChange(Event.SchemaChange.Change.CREATED, Event.SchemaChange.Target.TABLE, keyspace(), columnFamily());
         }