Less Invasive MultiGet_MultiSlice Implementation (#8)

* new iface

* Thrift

* More Thrift

* Cassandra server changes

* update tests

* no withOutAnderr

* CR - depend on abstraction

* Tighten the contract of MGMS

* Ban different-types and update tests

* fail sooner on invalid query (#12)

* fail sooner on invalid query

* iterate entry set instead of key set with lookups

build.xml

@@ -399,6 +399,7 @@
           <dependency groupId="org.jboss.byteman" artifactId="byteman" version="${byteman.version}" scope="test"/>
           <dependency groupId="org.jboss.byteman" artifactId="byteman-submit" version="${byteman.version}" scope="test"/>
           <dependency groupId="org.jboss.byteman" artifactId="byteman-bmunit" version="${byteman.version}" scope="test"/>
+          <dependency groupId="org.assertj" artifactId="assertj-core" version="3.12.0" scope="test"/>
 
 
           <dependency groupId="org.openjdk.jmh" artifactId="jmh-core" version="1.1.1"/>
@@ -479,6 +480,7 @@
                 artifactId="cassandra-parent"
                 version="${version}"/>
         <dependency groupId="junit" artifactId="junit"/>
+        <dependency groupId="org.assertj" artifactId="assertj-core"/>
         <dependency groupId="org.apache.rat" artifactId="apache-rat"/>
         <dependency groupId="org.apache.hadoop" artifactId="hadoop-core"/>
       	<dependency groupId="org.apache.hadoop" artifactId="hadoop-minicluster"/>
@@ -503,6 +505,7 @@
                 artifactId="cassandra-parent"
                 version="${version}"/>
         <dependency groupId="junit" artifactId="junit"/>
+        <dependency groupId="org.assertj" artifactId="assertj-core"/>
         <dependency groupId="org.apache.pig" artifactId="pig">
           <exclusion groupId="xmlenc" artifactId="xmlenc"/>
           <exclusion groupId="tomcat" artifactId="jasper-runtime"/>

interface/cassandra.thrift

@@ -55,7 +55,7 @@ namespace rb CassandraThrift
 # An effort should be made not to break forward-client-compatibility either
 # (e.g. one should avoid removing obsolete fields from the IDL), but no
 # guarantees in this respect are made by the Cassandra project.
-const string VERSION = "20.1.0-pt1"
+const string VERSION = "20.1.0-pt2"
 
 
 #
@@ -600,6 +600,15 @@ struct MultiSliceRequest {
     6: optional ConsistencyLevel consistency_level=ConsistencyLevel.ONE
 }
 
+/**
+ * A pair of a row (key) and selection of columns, used in calls to multiget_multislice() specifying which rows should
+ * be queried and which columns within said rows.
+ */
+struct KeyPredicate {
+    1: optional binary key,
+    2: optional SlicePredicate predicate,
+}
+
 service Cassandra {
   # auth methods
   void login(1: required AuthenticationRequest auth_request) throws (1:AuthenticationException authnx, 2:AuthorizationException authzx),
@@ -649,11 +658,21 @@ service Cassandra {
 
   /**
     Performs multiple get_slice commands in parallel for the given column_parent. Differently from multiget_slice,
-    users may specify a distinct <code>SlicePredicate</code> for each key in the <code>request</code>.
+    users may specify more than one <code>KeyPredicate</code> for each distinct key in the <code>request</code>.
+
+    Each list of <code>ColumnOrSuperColumn</code> present in the list associated with a specific key in the result
+    map corresponds to the result of a get_slice for one of the <code>KeyPredicate</code>s provided that matches
+    that key.
+
+    If there is more than one <code>KeyPredicate</code> associated with a specific key, we require that the types
+    of associated <code>SlicePredicate</code>s are of the same type (where type is defined as named columns,
+    slice range or reversed slice range).
+
+    We also do not make guarantees on the ordering of the lists for each key.
   */
-  map<binary,list<ColumnOrSuperColumn>> multiget_multislice(1:required map<binary, SlicePredicate> request,
-                                                            2:required ColumnParent column_parent,
-                                                            3:required ConsistencyLevel consistency_level=ConsistencyLevel.ONE)
+  map<binary,list<list<ColumnOrSuperColumn>>> multiget_multislice(1:required list<KeyPredicate> request,
+                                                                  2:required ColumnParent column_parent,
+                                                                  3:required ConsistencyLevel consistency_level=ConsistencyLevel.ONE)
                                         throws (1:InvalidRequestException ire, 2:UnavailableException ue, 3:TimedOutException te),
 
   /**