groupBy v2: Better error message when resources are exhausted. (#4046)

* groupBy v2: Better error message when resources are exhausted.

Fixes #4043.

* Fix tests.

processing/src/main/java/io/druid/query/groupby/GroupByQueryHelper.java

@@ -256,4 +256,18 @@ public class GroupByQueryHelper
     // Don't include post-aggregators since we don't know what types they are.
     return types.build();
   }
+
+  /**
+   * Throw a {@link ResourceLimitExceededException}. Only used by groupBy v2 when accumulation resources
+   * are exceeded, triggered by false return from {@link io.druid.query.groupby.epinephelinae.Grouper#aggregate(Object)}.
+   *
+   * @return nothing will ever be returned; this return type is for your convenience, similar to
+   * Throwables.propagate in Guava.
+   */
+  public static ResourceLimitExceededException throwAccumulationResourceLimitExceededException()
+  {
+    throw new ResourceLimitExceededException(
+        "Not enough resources to execute this query. Try increasing druid.query.groupBy.maxOnDiskStorage, "
+        + "druid.query.groupBy.maxMergingDictionarySize, or druid.processing.buffer.sizeBytes.");
+  }
 }

processing/src/main/java/io/druid/query/groupby/epinephelinae/GroupByMergingQueryRunnerV2.java

@@ -52,10 +52,10 @@ import io.druid.query.QueryContextKeys;
 import io.druid.query.QueryInterruptedException;
 import io.druid.query.QueryRunner;
 import io.druid.query.QueryWatcher;
-import io.druid.query.ResourceLimitExceededException;
 import io.druid.query.aggregation.AggregatorFactory;
 import io.druid.query.groupby.GroupByQuery;
 import io.druid.query.groupby.GroupByQueryConfig;
+import io.druid.query.groupby.GroupByQueryHelper;
 import io.druid.query.groupby.epinephelinae.RowBasedGrouperHelper.RowBasedKey;
 
 import java.io.Closeable;
@@ -313,7 +313,7 @@ public class GroupByMergingQueryRunnerV2 implements QueryRunner<Row>
       for (Boolean result : results) {
         if (!result) {
           future.cancel(true);
-          throw new ResourceLimitExceededException("Grouping resources exhausted");
+          throw GroupByQueryHelper.throwAccumulationResourceLimitExceededException();
         }
       }
     }

processing/src/main/java/io/druid/query/groupby/epinephelinae/GroupByRowProcessor.java

@@ -33,12 +33,12 @@ import io.druid.java.util.common.guava.CloseQuietly;
 import io.druid.java.util.common.guava.FilteredSequence;
 import io.druid.java.util.common.guava.Sequence;
 import io.druid.query.Query;
-import io.druid.query.ResourceLimitExceededException;
 import io.druid.query.aggregation.AggregatorFactory;
 import io.druid.query.filter.Filter;
 import io.druid.query.filter.ValueMatcher;
 import io.druid.query.groupby.GroupByQuery;
 import io.druid.query.groupby.GroupByQueryConfig;
+import io.druid.query.groupby.GroupByQueryHelper;
 import io.druid.query.groupby.RowBasedColumnSelectorFactory;
 import io.druid.query.groupby.epinephelinae.RowBasedGrouperHelper.RowBasedKey;
 import io.druid.query.groupby.resource.GroupByQueryResource;
@@ -168,7 +168,7 @@ public class GroupByRowProcessor
                   accumulator
               );
               if (retVal != grouper) {
-                throw new ResourceLimitExceededException("Grouping resources exhausted");
+                throw GroupByQueryHelper.throwAccumulationResourceLimitExceededException();
               }
 
               return RowBasedGrouperHelper.makeGrouperIterator(

processing/src/test/java/io/druid/query/groupby/GroupByQueryRunnerTest.java

@@ -1263,7 +1263,7 @@ public class GroupByQueryRunnerTest
     List<Row> expectedResults = null;
     if (config.getDefaultStrategy().equals(GroupByStrategySelector.STRATEGY_V2)) {
       expectedException.expect(ResourceLimitExceededException.class);
-      expectedException.expectMessage("Grouping resources exhausted");
+      expectedException.expectMessage("Not enough resources to execute this query");
     } else {
       expectedResults = Arrays.asList(
           GroupByQueryRunnerTestHelper.createExpectedRow("2011-04-01", "alias", "automotive", "rows", 1L, "idx", 135L),
@@ -1336,7 +1336,7 @@ public class GroupByQueryRunnerTest
       GroupByQueryRunnerTestHelper.runQuery(factory, runner, query);
     } else {
       expectedException.expect(ResourceLimitExceededException.class);
-      expectedException.expectMessage("Grouping resources exhausted");
+      expectedException.expectMessage("Not enough resources to execute this query");
       GroupByQueryRunnerTestHelper.runQuery(factory, runner, query);
     }
   }