From 91d4193053ae2fc8e1707213d8d5fe78a9b2d2f8 Mon Sep 17 00:00:00 2001
From: Hsuan-Yi Chu <hsuanyi@usc.edu>
Date: Thu, 12 Nov 2015 15:01:10 -0800
Subject: [PATCH] DRILL-4083: ScanPrel's CPU cost should not be zero even if
 column count is zero

---
 .../apache/drill/exec/hive/TestHiveStorage.java   | 15 +++++++++++++++
 .../drill/exec/planner/physical/ScanPrel.java     |  5 +++--
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/contrib/storage-hive/core/src/test/java/org/apache/drill/exec/hive/TestHiveStorage.java b/contrib/storage-hive/core/src/test/java/org/apache/drill/exec/hive/TestHiveStorage.java
index 1112e8c0b4c..9d784fe11dc 100644
--- a/contrib/storage-hive/core/src/test/java/org/apache/drill/exec/hive/TestHiveStorage.java
+++ b/contrib/storage-hive/core/src/test/java/org/apache/drill/exec/hive/TestHiveStorage.java
@@ -36,6 +36,21 @@ public static void setupOptions() throws Exception {
     test(String.format("alter session set `%s` = true", PlannerSettings.ENABLE_DECIMAL_DATA_TYPE_KEY));
   }
 
+
+  @Test // DRILL-4083
+  public void testNativeScanWhenNoColumnIsRead() throws Exception {
+    try {
+      test(String.format("alter session set `%s` = true", ExecConstants.HIVE_OPTIMIZE_SCAN_WITH_NATIVE_READERS));
+
+      String query = "SELECT count(*) FROM hive.readtest_parquet";
+      testPhysicalPlan(query, "hive-drill-native-parquet-scan");
+    } finally {
+      test(String.format("alter session set `%s` = %s",
+          ExecConstants.HIVE_OPTIMIZE_SCAN_WITH_NATIVE_READERS,
+              ExecConstants.HIVE_OPTIMIZE_SCAN_WITH_NATIVE_READERS_VALIDATOR.getDefault().bool_val ? "true" : "false"));
+    }
+  }
+
   @Test
   public void hiveReadWithDb() throws Exception {
     test("select * from hive.kv");
diff --git a/exec/java-exec/src/main/java/org/apache/drill/exec/planner/physical/ScanPrel.java b/exec/java-exec/src/main/java/org/apache/drill/exec/planner/physical/ScanPrel.java
index f69ee4c009f..b100d903f05 100644
--- a/exec/java-exec/src/main/java/org/apache/drill/exec/planner/physical/ScanPrel.java
+++ b/exec/java-exec/src/main/java/org/apache/drill/exec/planner/physical/ScanPrel.java
@@ -118,8 +118,9 @@ public RelOptCost computeSelfCost(final RelOptPlanner planner) {
     // double rowCount = RelMetadataQuery.getRowCount(this);
     double rowCount = stats.getRecordCount();
 
-
-    double cpuCost = rowCount * columnCount; // for now, assume cpu cost is proportional to row count.
+    // As DRILL-4083 points out, when columnCount == 0, cpuCost becomes zero,
+    // which makes the costs of HiveScan and HiveDrillNativeParquetScan the same
+    double cpuCost = rowCount * Math.max(columnCount, 1); // For now, assume cpu cost is proportional to row count.
 
     // If a positive value for CPU cost is given multiply the default CPU cost by given CPU cost.
     if (stats.getCpuCost() > 0) {