Rework EXPLAIN for planner's buffer usage.

Commit ce77abe6 allowed EXPLAIN (BUFFERS) to report the information
on buffer usage during planning phase. However three issues were
reported regarding this feature.

(1) Previously, EXPLAIN option BUFFERS required ANALYZE. So the query
    had to be actually executed by specifying ANALYZE even when we
    want to see only the planner's buffer usage. This was inconvenient
    especially when the query was write one like DELETE.

(2) EXPLAIN included the planner's buffer usage in summary
    information. So SUMMARY option had to be enabled to report that.
    Also this format was confusing.

(3) The output structure for planning information was not consistent
    between TEXT format and the others. For example, "Planning" tag
    was output in JSON format, but not in TEXT format.

For (1), this commit allows us to perform EXPLAIN (BUFFERS) without
ANALYZE to report the planner's buffer usage.

For (2), this commit changed EXPLAIN output so that the planner's
buffer usage is reported before summary information.

For (3), this commit made the output structure for planning
information more consistent between the formats.

Back-patch to v13 where the planner's buffer usage was allowed to
be reported in EXPLAIN.

Reported-by: Pierre Giraud, David Rowley
Author: Fujii Masao
Reviewed-by: David Rowley, Julien Rouhaud, Pierre Giraud
Discussion: https://postgr.es/m/07b226e6-fa49-687f-b110-b7c37572f69e@dalibo.com

doc/src/sgml/ref/explain.sgml

@@ -187,8 +187,7 @@ ROLLBACK;
       query processing.
       The number of blocks shown for an
       upper-level node includes those used by all its child nodes.  In text
-      format, only non-zero values are printed.  This parameter may only be
-      used when <literal>ANALYZE</literal> is also enabled.  It defaults to
+      format, only non-zero values are printed.  It defaults to
       <literal>FALSE</literal>.
      </para>
     </listitem>

src/backend/commands/explain.c

@@ -116,7 +116,8 @@ static void show_instrumentation_count(const char *qlabel, int which,
 static void show_foreignscan_info(ForeignScanState *fsstate, ExplainState *es);
 static void show_eval_params(Bitmapset *bms_params, ExplainState *es);
 static const char *explain_get_index_name(Oid indexId);
-static void show_buffer_usage(ExplainState *es, const BufferUsage *usage);
+static void show_buffer_usage(ExplainState *es, const BufferUsage *usage,
+							  bool planning);
 static void show_wal_usage(ExplainState *es, const WalUsage *usage);
 static void ExplainIndexScanDetails(Oid indexid, ScanDirection indexorderdir,
 									ExplainState *es);
@@ -221,11 +222,6 @@ ExplainQuery(ParseState *pstate, ExplainStmt *stmt,
 					 parser_errposition(pstate, opt->location)));
 	}
 
-	if (es->buffers && !es->analyze)
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-				 errmsg("EXPLAIN option BUFFERS requires ANALYZE")));
-
 	if (es->wal && !es->analyze)
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
@@ -586,8 +582,13 @@ ExplainOnePlan(PlannedStmt *plannedstmt, IntoClause *into, ExplainState *es,
 	/* Create textual dump of plan tree */
 	ExplainPrintPlan(es, queryDesc);
 
-	if (es->summary && (planduration || bufusage))
+	/* Show buffer usage in planning */
+	if (bufusage)
+	{
 		ExplainOpenGroup("Planning", "Planning", true, es);
+		show_buffer_usage(es, bufusage, true);
+		ExplainCloseGroup("Planning", "Planning", true, es);
+	}
 
 	if (es->summary && planduration)
 	{
@@ -596,19 +597,6 @@ ExplainOnePlan(PlannedStmt *plannedstmt, IntoClause *into, ExplainState *es,
 		ExplainPropertyFloat("Planning Time", "ms", 1000.0 * plantime, 3, es);
 	}
 
-	/* Show buffer usage */
-	if (es->summary && bufusage)
-	{
-		if (es->format == EXPLAIN_FORMAT_TEXT)
-			es->indent++;
-		show_buffer_usage(es, bufusage);
-		if (es->format == EXPLAIN_FORMAT_TEXT)
-			es->indent--;
-	}
-
-	if (es->summary && (planduration || bufusage))
-		ExplainCloseGroup("Planning", "Planning", true, es);
-
 	/* Print info about runtime of triggers */
 	if (es->analyze)
 		ExplainPrintTriggers(es, queryDesc);
@@ -1996,7 +1984,7 @@ ExplainNode(PlanState *planstate, List *ancestors,
 
 	/* Show buffer/WAL usage */
 	if (es->buffers && planstate->instrument)
-		show_buffer_usage(es, &planstate->instrument->bufusage);
+		show_buffer_usage(es, &planstate->instrument->bufusage, false);
 	if (es->wal && planstate->instrument)
 		show_wal_usage(es, &planstate->instrument->walusage);
 
@@ -2015,7 +2003,7 @@ ExplainNode(PlanState *planstate, List *ancestors,
 
 			ExplainOpenWorker(n, es);
 			if (es->buffers)
-				show_buffer_usage(es, &instrument->bufusage);
+				show_buffer_usage(es, &instrument->bufusage, false);
 			if (es->wal)
 				show_wal_usage(es, &instrument->walusage);
 			ExplainCloseWorker(n, es);
@@ -3301,7 +3289,7 @@ explain_get_index_name(Oid indexId)
  * Show buffer usage details.
  */
 static void
-show_buffer_usage(ExplainState *es, const BufferUsage *usage)
+show_buffer_usage(ExplainState *es, const BufferUsage *usage, bool planning)
 {
 	if (es->format == EXPLAIN_FORMAT_TEXT)
 	{
@@ -3317,6 +3305,15 @@ show_buffer_usage(ExplainState *es, const BufferUsage *usage)
 								usage->temp_blks_written > 0);
 		bool		has_timing = (!INSTR_TIME_IS_ZERO(usage->blk_read_time) ||
 								  !INSTR_TIME_IS_ZERO(usage->blk_write_time));
+		bool		show_planning = (planning && (has_shared ||
+												  has_local || has_temp || has_timing));
+
+		if (show_planning)
+		{
+			ExplainIndentText(es);
+			appendStringInfoString(es->str, "Planning:\n");
+			es->indent++;
+		}
 
 		/* Show only positive counter values. */
 		if (has_shared || has_local || has_temp)
@@ -3386,6 +3383,9 @@ show_buffer_usage(ExplainState *es, const BufferUsage *usage)
 								 INSTR_TIME_GET_MILLISEC(usage->blk_write_time));
 			appendStringInfoChar(es->str, '\n');
 		}
+
+		if (show_planning)
+			es->indent--;
 	}
 	else
 	{

src/test/regress/expected/explain.out

@@ -106,7 +106,6 @@ select explain_filter('explain (analyze, buffers, format json) select * from int
        "Temp Written Blocks": N    +
      },                            +
      "Planning": {                 +
-       "Planning Time": N.N,       +
        "Shared Hit Blocks": N,     +
        "Shared Read Blocks": N,    +
        "Shared Dirtied Blocks": N, +
@@ -118,6 +117,7 @@ select explain_filter('explain (analyze, buffers, format json) select * from int
        "Temp Read Blocks": N,      +
        "Temp Written Blocks": N    +
      },                            +
+     "Planning Time": N.N,         +
      "Triggers": [                 +
      ],                            +
      "Execution Time": N.N         +
@@ -155,7 +155,6 @@ select explain_filter('explain (analyze, buffers, format xml) select * from int8
        <Temp-Written-Blocks>N</Temp-Written-Blocks>    +
      </Plan>                                           +
      <Planning>                                        +
-       <Planning-Time>N.N</Planning-Time>              +
        <Shared-Hit-Blocks>N</Shared-Hit-Blocks>        +
        <Shared-Read-Blocks>N</Shared-Read-Blocks>      +
        <Shared-Dirtied-Blocks>N</Shared-Dirtied-Blocks>+
@@ -167,6 +166,7 @@ select explain_filter('explain (analyze, buffers, format xml) select * from int8
        <Temp-Read-Blocks>N</Temp-Read-Blocks>          +
        <Temp-Written-Blocks>N</Temp-Written-Blocks>    +
      </Planning>                                       +
+     <Planning-Time>N.N</Planning-Time>                +
      <Triggers>                                        +
      </Triggers>                                       +
      <Execution-Time>N.N</Execution-Time>              +
@@ -201,7 +201,6 @@ select explain_filter('explain (analyze, buffers, format yaml) select * from int
      Temp Read Blocks: N      +
      Temp Written Blocks: N   +
    Planning:                  +
-     Planning Time: N.N       +
      Shared Hit Blocks: N     +
      Shared Read Blocks: N    +
      Shared Dirtied Blocks: N +
@@ -212,10 +211,58 @@ select explain_filter('explain (analyze, buffers, format yaml) select * from int
      Local Written Blocks: N  +
      Temp Read Blocks: N      +
      Temp Written Blocks: N   +
+   Planning Time: N.N         +
    Triggers:                  +
    Execution Time: N.N
 (1 row)
 
+select explain_filter('explain (buffers, format text) select * from int8_tbl i8');
+                     explain_filter                      
+---------------------------------------------------------
+ Seq Scan on int8_tbl i8  (cost=N.N..N.N rows=N width=N)
+(1 row)
+
+select explain_filter('explain (buffers, format json) select * from int8_tbl i8');
+           explain_filter           
+------------------------------------
+ [                                 +
+   {                               +
+     "Plan": {                     +
+       "Node Type": "Seq Scan",    +
+       "Parallel Aware": false,    +
+       "Relation Name": "int8_tbl",+
+       "Alias": "i8",              +
+       "Startup Cost": N.N,        +
+       "Total Cost": N.N,          +
+       "Plan Rows": N,             +
+       "Plan Width": N,            +
+       "Shared Hit Blocks": N,     +
+       "Shared Read Blocks": N,    +
+       "Shared Dirtied Blocks": N, +
+       "Shared Written Blocks": N, +
+       "Local Hit Blocks": N,      +
+       "Local Read Blocks": N,     +
+       "Local Dirtied Blocks": N,  +
+       "Local Written Blocks": N,  +
+       "Temp Read Blocks": N,      +
+       "Temp Written Blocks": N    +
+     },                            +
+     "Planning": {                 +
+       "Shared Hit Blocks": N,     +
+       "Shared Read Blocks": N,    +
+       "Shared Dirtied Blocks": N, +
+       "Shared Written Blocks": N, +
+       "Local Hit Blocks": N,      +
+       "Local Read Blocks": N,     +
+       "Local Dirtied Blocks": N,  +
+       "Local Written Blocks": N,  +
+       "Temp Read Blocks": N,      +
+       "Temp Written Blocks": N    +
+     }                             +
+   }                               +
+ ]
+(1 row)
+
 -- SETTINGS option
 -- We have to ignore other settings that might be imposed by the environment,
 -- so printing the whole Settings field unfortunately won't do.
@@ -402,7 +449,6 @@ select jsonb_pretty(
              "Shared Written Blocks": 0                     +
          },                                                 +
          "Planning": {                                      +
-             "Planning Time": 0.0,                          +
              "Local Hit Blocks": 0,                         +
              "Temp Read Blocks": 0,                         +
              "Local Read Blocks": 0,                        +
@@ -416,6 +462,7 @@ select jsonb_pretty(
          },                                                 +
          "Triggers": [                                      +
          ],                                                 +
+         "Planning Time": 0.0,                              +
          "Execution Time": 0.0                              +
      }                                                      +
  ]

src/test/regress/sql/explain.sql

@@ -57,6 +57,8 @@ select explain_filter('explain (analyze, buffers, format text) select * from int
 select explain_filter('explain (analyze, buffers, format json) select * from int8_tbl i8');
 select explain_filter('explain (analyze, buffers, format xml) select * from int8_tbl i8');
 select explain_filter('explain (analyze, buffers, format yaml) select * from int8_tbl i8');
+select explain_filter('explain (buffers, format text) select * from int8_tbl i8');
+select explain_filter('explain (buffers, format json) select * from int8_tbl i8');
 
 -- SETTINGS option
 -- We have to ignore other settings that might be imposed by the environment,