implement `USE <keyspace>' statement

Patch by eevans

git-svn-id: https://svn.apache.org/repos/asf/cassandra/trunk@1029362 13f79535-47bb-0310-9956-ffa450edef68

doc/cql/CQL.textile

@@ -4,6 +4,15 @@ h2. Table of Contents
 
 {toc}
 
+h2. USE
+
+__Synopsis:__
+
+bc. 
+USE <KEYSPACE>;
+
+A @USE@ statement consists of the @USE@ keyword, followed by a valid keyspace name.  Its purpose is to assign the per-connection, current working keyspace.  All subsequent keyspace-specific actions will be performed in the context of the supplied value.
+
 h2. SELECT
 
 __Synopsis:__

src/java/org/apache/cassandra/avro/CassandraServer.java

@@ -1208,7 +1208,7 @@ public class CassandraServer implements Cassandra {
         
         try
         {
-            return QueryProcessor.process(queryString, state().getKeyspace());
+            return QueryProcessor.process(queryString, state());
         }
         catch (RecognitionException e)
         {

src/java/org/apache/cassandra/cql/Cql.g

@@ -16,6 +16,12 @@ options {
 query returns [CQLStatement stmnt]
     : selectStatement { $stmnt = new CQLStatement(StatementType.SELECT, $selectStatement.expr); }
     | updateStatement { $stmnt = new CQLStatement(StatementType.UPDATE, $updateStatement.expr); }
+    | useStatement    { $stmnt = new CQLStatement(StatementType.USE, $useStatement.keyspace); }
+    ;
+
+// USE <KEYSPACE>;
+useStatement returns [String keyspace]
+    : K_USE IDENT { $keyspace = $IDENT.text; } ';'
     ;
 
 /**
@@ -127,6 +133,7 @@ K_LEVEL:       ( Z E R O
                | D C Q U O R U M S Y N C
                )
                ;
+K_USE:         U S E;
 
 // Case-insensitive alpha characters
 fragment A: ('a'|'A');

src/java/org/apache/cassandra/cql/QueryProcessor.java

@@ -54,6 +54,7 @@ import org.apache.cassandra.db.filter.QueryPath;
 import org.apache.cassandra.dht.AbstractBounds;
 import org.apache.cassandra.dht.Bounds;
 import org.apache.cassandra.dht.IPartitioner;
+import org.apache.cassandra.service.ClientState;
 import org.apache.cassandra.service.StorageProxy;
 import org.apache.cassandra.service.StorageService;
 import org.apache.cassandra.thrift.ConsistencyLevel;
@@ -105,13 +106,14 @@ public class QueryProcessor
         return columnFamilyKeyMap;
     }
 
-    public static CqlResult process(String queryString, String keyspace)
+    public static CqlResult process(String queryString, ClientState clientState)
     throws RecognitionException, UnavailableException, InvalidRequestException, TimedOutException
     {
         logger.debug("CQL QUERY: {}", queryString);
         
         CqlParser parser = getParser(queryString);
         CQLStatement statement = parser.query();
+        String keyspace = clientState.getKeyspace();
         
         CqlResult avroResult = new CqlResult();
         
@@ -283,6 +285,12 @@ public class QueryProcessor
                     throw new TimedOutException();
                 }
                     
+                return avroResult;
+                
+            case USE:
+                clientState.setKeyspace((String)statement.statement);
+                avroResult.type = CqlResultType.VOID;
+                
                 return avroResult;
         }
         

src/java/org/apache/cassandra/cql/StatementType.java

@@ -23,5 +23,5 @@ package org.apache.cassandra.cql;
 
 public enum StatementType
 {
-    SELECT, UPDATE;
+    SELECT, UPDATE, USE;
 }