Cassandra stress user defined writes should populate sequentially

Patch by tjake; reviewed by Benedict for CASSANDRA-8524

CHANGES.txt

@@ -1,4 +1,5 @@
 2.1.3
+ * Stress - user defined writes should populate sequentally (CASSANDRA-8524)
  * Fix regression in SSTableRewriter causing some rows to become unreadable 
    during compaction (CASSANDRA-8429)
  * Run major compactions for repaired/unrepaired in parallel (CASSANDRA-8510)

tools/stress/src/org/apache/cassandra/stress/settings/SettingsCommandUser.java

@@ -65,6 +65,11 @@ public class SettingsCommandUser extends SettingsCommand
             throw new IllegalArgumentException("Must specify at least one command with a non-zero ratio");
     }
 
+    public boolean hasInsertOnly()
+    {
+        return ratios.size() == 1 && ratios.containsKey("insert");
+    }
+
     public OpDistributionFactory getFactory(final StressSettings settings)
     {
         final SeedManager seeds = new SeedManager(settings);

tools/stress/src/org/apache/cassandra/stress/settings/SettingsPopulation.java

@@ -134,6 +134,11 @@ public class SettingsPopulation implements Serializable
         String[] params = clArgs.remove("-pop");
         if (params == null)
         {
+            if (command instanceof SettingsCommandUser && ((SettingsCommandUser)command).hasInsertOnly())
+            {
+                return new SettingsPopulation(new SequentialOptions(defaultLimit));
+            }
+
             // return defaults:
             switch(command.type)
             {