Distributed EXPLAIN: Generate valid JSON output.

This modifies the EXPLAIN output functions to actually generate
valid JSON output when (FORMAT JSON) is being used.

Fixes #494.

src/backend/distributed/planner/multi_explain.c

@@ -196,6 +196,10 @@ MultiExplainOneQuery(Query *query, IntoClause *into, ExplainState *es,
 
 		es->indent += 1;
 	}
+	else if (es->format == EXPLAIN_FORMAT_JSON)
+	{
+		ExplainOpenGroup("Distributed Query", NULL, true, es);
+	}
 
 	routerExecutablePlan = RouterExecutablePlan(multiPlan, TaskExecutorType);
 
@@ -245,6 +249,13 @@ MultiExplainOneQuery(Query *query, IntoClause *into, ExplainState *es,
 			appendStringInfo(es->str, "Master Query\n");
 			es->indent += 1;
 		}
+		else if (es->format == EXPLAIN_FORMAT_JSON)
+		{
+			ExplainJSONLineEnding(es);
+			appendStringInfoSpaces(es->str, es->indent * 2);
+			appendStringInfo(es->str, "\"Master Query\":");
+			es->grouping_stack = lcons_int(0, es->grouping_stack);
+		}
 
 		ExplainMasterPlan(masterPlan, into, es, queryString, params, &planDuration);
 
@@ -253,6 +264,11 @@ MultiExplainOneQuery(Query *query, IntoClause *into, ExplainState *es,
 			es->indent -= 1;
 		}
 	}
+
+	if (es->format == EXPLAIN_FORMAT_JSON)
+	{
+		ExplainCloseGroup("Distributed Query", NULL, true, es);
+	}
 }
 
 
@@ -390,7 +406,7 @@ ExplainJob(Job *job, ExplainState *es)
 	List *taskList = job->taskList;
 	int taskCount = list_length(taskList);
 
-	ExplainOpenGroup("Job", NULL, true, es);
+	ExplainOpenGroup("Job", "Job", true, es);
 
 	ExplainPropertyInteger("Task Count", taskCount, es);
 
@@ -424,7 +440,7 @@ ExplainJob(Job *job, ExplainState *es)
 		ExplainCloseGroup("Tasks", "Tasks", false, es);
 	}
 
-	ExplainCloseGroup("Job", NULL, true, es);
+	ExplainCloseGroup("Job", "Job", true, es);
 
 	/* show explain output for depended jobs, if any */
 	foreach(dependedJobCell, dependedJobList)

src/test/regress/expected/multi_explain.out

@@ -28,8 +28,9 @@ EXPLAIN (COSTS FALSE, FORMAT JSON)
 	SELECT l_quantity, count(*) count_quantity FROM lineitem
 	GROUP BY l_quantity ORDER BY count_quantity, l_quantity;
 [
-  "Executor": "Real-Time",
   {
+    "Executor": "Real-Time",
+    "Job": {
       "Task Count": 6,
       "Tasks Shown": "One of 6",
       "Tasks": [
@@ -58,6 +59,7 @@ EXPLAIN (COSTS FALSE, FORMAT JSON)
         }
       ]
     },
+    "Master Query":
     {
       "Plan": {
         "Node Type": "Sort",
@@ -80,6 +82,7 @@ EXPLAIN (COSTS FALSE, FORMAT JSON)
         ]
       }
     }
+  }
 ]
 -- Test XML format
 EXPLAIN (COSTS FALSE, FORMAT XML)
@@ -150,7 +153,8 @@ EXPLAIN (COSTS FALSE, FORMAT YAML)
 	SELECT l_quantity, count(*) count_quantity FROM lineitem
 	GROUP BY l_quantity ORDER BY count_quantity, l_quantity;
 Executor: "Real-Time"
-- Task Count: 6
+Job: 
+  Task Count: 6
   Tasks Shown: "One of 6"
   Tasks: 
     - Node: "host=localhost port=57637 dbname=regression"