DRILL-7160: e.q.max_rows QUERY-level option shown even if not set

The fix is to force setting to zero IFF autoLimit was intended to be set originally but is inapplicable; such as 'SHOW DATABASES'. If autolimit was not intended to be applied, setting the value to zero is not required.
WebUI is also patched to not show the zero value set in such scenarios.

Author: Kunal Khatua

exec/java-exec/src/main/java/org/apache/drill/exec/planner/sql/DrillSqlWorker.java

@@ -216,27 +216,31 @@ private static PhysicalPlan getQueryPlan(QueryContext context, String sql, Point
     return handler.getPlan(sqlNode);
   }
 
-  private static boolean isAutoLimitShouldBeApplied(QueryContext context, SqlNode sqlNode) {
-    return (context.getOptions().getOption(ExecConstants.QUERY_MAX_ROWS).num_val.intValue() > 0) && sqlNode.getKind().belongsTo(SqlKind.QUERY)
-        && (sqlNode.getKind() != SqlKind.ORDER_BY || isAutoLimitLessThanOrderByFetch((SqlOrderBy) sqlNode, context));
+  private static boolean isAutoLimitShouldBeApplied(SqlNode sqlNode, int queryMaxRows) {
+    return (queryMaxRows > 0) && sqlNode.getKind().belongsTo(SqlKind.QUERY)
+        && (sqlNode.getKind() != SqlKind.ORDER_BY || isAutoLimitLessThanOrderByFetch((SqlOrderBy) sqlNode, queryMaxRows));
   }
 
   private static SqlNode checkAndApplyAutoLimit(SqlConverter parser, QueryContext context, String sql) {
     SqlNode sqlNode = parser.parse(sql);
-    if (isAutoLimitShouldBeApplied(context, sqlNode)) {
-      sqlNode = wrapWithAutoLimit(sqlNode, context);
+    int queryMaxRows = context.getOptions().getOption(ExecConstants.QUERY_MAX_ROWS).num_val.intValue();
+    if (isAutoLimitShouldBeApplied(sqlNode, queryMaxRows)) {
+      sqlNode = wrapWithAutoLimit(sqlNode, queryMaxRows);
     } else {
-      context.getOptions().setLocalOption(ExecConstants.QUERY_MAX_ROWS, 0);
+      //Force setting to zero IFF autoLimit was intended to be set originally but is inapplicable
+      if (queryMaxRows > 0) {
+        context.getOptions().setLocalOption(ExecConstants.QUERY_MAX_ROWS, 0);
+      }
     }
     return sqlNode;
   }
 
-  private static boolean isAutoLimitLessThanOrderByFetch(SqlOrderBy orderBy, QueryContext context) {
-    return orderBy.fetch == null || Integer.parseInt(orderBy.fetch.toString()) > context.getOptions().getOption(ExecConstants.QUERY_MAX_ROWS).num_val.intValue();
+  private static boolean isAutoLimitLessThanOrderByFetch(SqlOrderBy orderBy, int queryMaxRows) {
+    return orderBy.fetch == null || Integer.parseInt(orderBy.fetch.toString()) > queryMaxRows;
   }
 
-  private static SqlNode wrapWithAutoLimit(SqlNode sqlNode, QueryContext context) {
-    SqlNumericLiteral autoLimitLiteral = SqlLiteral.createExactNumeric(String.valueOf(context.getOptions().getOption(ExecConstants.QUERY_MAX_ROWS).num_val.intValue()), SqlParserPos.ZERO);
+  private static SqlNode wrapWithAutoLimit(SqlNode sqlNode, int queryMaxRows) {
+    SqlNumericLiteral autoLimitLiteral = SqlLiteral.createExactNumeric(String.valueOf(queryMaxRows), SqlParserPos.ZERO);
     if (sqlNode.getKind() == SqlKind.ORDER_BY) {
       SqlOrderBy orderBy = (SqlOrderBy) sqlNode;
       return new SqlOrderBy(orderBy.getParserPosition(), orderBy.query, orderBy.orderList, orderBy.offset, autoLimitLiteral);

exec/java-exec/src/main/java/org/apache/drill/exec/server/rest/QueryWrapper.java

@@ -22,6 +22,7 @@
 
 import org.apache.drill.common.exceptions.UserException;
 import org.apache.drill.common.exceptions.UserRemoteException;
+import org.apache.drill.exec.ExecConstants;
 import org.apache.drill.exec.proto.UserBitShared.QueryId;
 import org.apache.drill.exec.proto.UserBitShared.QueryResult.QueryState;
 import org.apache.drill.exec.proto.UserBitShared.QueryType;
@@ -77,7 +78,14 @@ public QueryResult run(final WorkManager workManager, final WebUserConnection we
         .setAutolimitRowcount(autoLimitRowCount)
         .build();
 
-    webUserConnection.setAutoLimitRowCount(autoLimitRowCount);
+    int defaultMaxRows = webUserConnection.getSession().getOptions().getOption(ExecConstants.QUERY_MAX_ROWS).num_val.intValue();
+    int maxRows;
+    if (autoLimitRowCount > 0 && defaultMaxRows > 0) {
+      maxRows = Math.min(autoLimitRowCount, defaultMaxRows);
+    } else {
+      maxRows = Math.max(autoLimitRowCount, defaultMaxRows);
+    }
+    webUserConnection.setAutoLimitRowCount(maxRows);
 
     // Submit user query to Drillbit work queue.
     final QueryId queryId = workManager.getUserWorker().submitWork(webUserConnection, runQuery);