Function ExplainOneQuery

src/backend/commands/explain.c:506–568

* ExplainOneQuery - * print out the execution plan for one Query * * "into" is NULL unless we are explaining the contents of a CreateTableAsStmt. */

 * "into" is NULL unless we are explaining the contents of a CreateTableAsStmt.
 */
static void
ExplainOneQuery(Query *query, int cursorOptions,
				IntoClause *into, ExplainState *es,
				const char *queryString, ParamListInfo params,
				QueryEnvironment *queryEnv)
{
#ifdef USE_ORCA
	if (es->dxl)
	{
		ExplainDXL(query, es, queryString, params);
		return;
	}
#endif

	/* planner will not cope with utility statements */
	if (query->commandType == CMD_UTILITY)
	{
		ExplainOneUtility(query->utilityStmt, into, es, queryString, params,
						  queryEnv);
		return;
	}

	/* if an advisor plugin is present, let it manage things */
	if (ExplainOneQuery_hook)
		(*ExplainOneQuery_hook) (query, cursorOptions, into, es,
								 queryString, params, queryEnv);
	else
	{
		PlannedStmt *plan;
		instr_time	planstart,
					planduration;
		BufferUsage bufusage_start,
					bufusage;

		if (es->buffers)
			bufusage_start = pgBufferUsage;
		INSTR_TIME_SET_CURRENT(planstart);

		/* plan the query */
		plan = pg_plan_query(query, queryString, cursorOptions, params);

		INSTR_TIME_SET_CURRENT(planduration);
		INSTR_TIME_SUBTRACT(planduration, planstart);

		/*
		 * GPDB_92_MERGE_FIXME: it really should be an optimizer's responsibility
		 * to correctly set the into-clause and into-policy of the PlannedStmt.
		 */
		if (into != NULL)
			plan->intoClause = copyObject(into);

		/* calc differences of buffer counters. */
		if (es->buffers)
		{
			memset(&bufusage, 0, sizeof(BufferUsage));
			BufferUsageAccumDiff(&bufusage, &pgBufferUsage, &bufusage_start);
		}