Rework EXPLAIN format for incremental sort

The explain format used by incremental sort was somewhat inconsistent
with other nodes, making it harder to parse and understand. This commit
addresses that by

 - adding an extra space to better separate groups of values

 - using colons instead of equal signs to separate key/value

 - properly capitalizing first letter of a key

 - using separate lines for full and pre-sorted groups

These changes were proposed by Justin Pryzby and mostly copy the final
explain format used to report WAL usage.

Author: Justin Pryzby
Reviewed-by: James Coleman
Discussion: https://postgr.es/m/20200419023625.GP26953@telsasoft.com

src/backend/commands/explain.c

@@ -2798,9 +2798,9 @@ show_incremental_sort_group_info(IncrementalSortGroupInfo *groupInfo,
 			const char *spaceTypeName;
 
 			spaceTypeName = tuplesort_space_type_name(SORT_SPACE_TYPE_MEMORY);
-			appendStringInfo(es->str, " %s: avg=%ldkB peak=%ldkB",
+			appendStringInfo(es->str, "  Average %s: %ldkB  Peak %s: %ldkB",
 							 spaceTypeName, avgSpace,
-							 groupInfo->maxMemorySpaceUsed);
+							 spaceTypeName, groupInfo->maxMemorySpaceUsed);
 		}
 
 		if (groupInfo->maxDiskSpaceUsed > 0)
@@ -2810,12 +2810,9 @@ show_incremental_sort_group_info(IncrementalSortGroupInfo *groupInfo,
 			const char *spaceTypeName;
 
 			spaceTypeName = tuplesort_space_type_name(SORT_SPACE_TYPE_DISK);
-			/* Add a semicolon separator only if memory stats were printed. */
-			if (groupInfo->maxMemorySpaceUsed > 0)
-				appendStringInfo(es->str, ";");
-			appendStringInfo(es->str, " %s: avg=%ldkB peak=%ldkB",
+			appendStringInfo(es->str, "  Average %s: %ldkB  Peak %s: %ldkB",
 							 spaceTypeName, avgSpace,
-							 groupInfo->maxDiskSpaceUsed);
+							 spaceTypeName, groupInfo->maxDiskSpaceUsed);
 		}
 	}
 	else
@@ -2899,8 +2896,8 @@ show_incremental_sort_info(IncrementalSortState *incrsortstate,
 		if (prefixsortGroupInfo->groupCount > 0)
 		{
 			if (es->format == EXPLAIN_FORMAT_TEXT)
-				appendStringInfo(es->str, " ");
-			show_incremental_sort_group_info(prefixsortGroupInfo, "Presorted", false, es);
+				appendStringInfo(es->str, "\n");
+			show_incremental_sort_group_info(prefixsortGroupInfo, "Pre-sorted", true, es);
 		}
 		if (es->format == EXPLAIN_FORMAT_TEXT)
 			appendStringInfo(es->str, "\n");
@@ -2942,8 +2939,8 @@ show_incremental_sort_info(IncrementalSortState *incrsortstate,
 			if (prefixsortGroupInfo->groupCount > 0)
 			{
 				if (es->format == EXPLAIN_FORMAT_TEXT)
-					appendStringInfo(es->str, " ");
-				show_incremental_sort_group_info(prefixsortGroupInfo, "Presorted", false, es);
+					appendStringInfo(es->str, "\n");
+				show_incremental_sort_group_info(prefixsortGroupInfo, "Pre-sorted", true, es);
 			}
 			if (es->format == EXPLAIN_FORMAT_TEXT)
 				appendStringInfo(es->str, "\n");

src/test/regress/expected/incremental_sort.out

@@ -106,7 +106,7 @@ declare
   space_key text;
 begin
   for node in select * from jsonb_array_elements(explain_analyze_inc_sort_nodes(query)) t loop
-    for group_key in select unnest(array['Full-sort Groups', 'Presorted Groups']::text[]) t loop
+    for group_key in select unnest(array['Full-sort Groups', 'Pre-sorted Groups']::text[]) t loop
       for space_key in select unnest(array['Sort Space Memory', 'Sort Space Disk']::text[]) t loop
         node := jsonb_set(node, array[group_key, space_key, 'Average Sort Space Used'], '"NN"', false);
         node := jsonb_set(node, array[group_key, space_key, 'Peak Sort Space Used'], '"NN"', false);
@@ -128,7 +128,7 @@ declare
   space_key text;
 begin
   for node in select * from jsonb_array_elements(explain_analyze_inc_sort_nodes(query)) t loop
-    for group_key in select unnest(array['Full-sort Groups', 'Presorted Groups']::text[]) t loop
+    for group_key in select unnest(array['Full-sort Groups', 'Pre-sorted Groups']::text[]) t loop
       group_stats := node->group_key;
       for space_key in select unnest(array['Sort Space Memory', 'Sort Space Disk']::text[]) t loop
         if (group_stats->space_key->'Peak Sort Space Used')::bigint < (group_stats->space_key->'Peak Sort Space Used')::bigint then
@@ -534,12 +534,12 @@ select * from (select * from t order by a) s order by a, b limit 55;
 -- Test EXPLAIN ANALYZE with only a fullsort group.
 select explain_analyze_without_memory('select * from (select * from t order by a) s order by a, b limit 55');
                                         explain_analyze_without_memory                                         
-------------------------------------------------------------------------------------------------
+---------------------------------------------------------------------------------------------------------------
  Limit (actual rows=55 loops=1)
    ->  Incremental Sort (actual rows=55 loops=1)
          Sort Key: t.a, t.b
          Presorted Key: t.a
-         Full-sort Groups: 2 Sort Methods: top-N heapsort, quicksort Memory: avg=NNkB peak=NNkB
+         Full-sort Groups: 2  Sort Methods: top-N heapsort, quicksort  Average Memory: NNkB  Peak Memory: NNkB
          ->  Sort (actual rows=101 loops=1)
                Sort Key: t.a
                Sort Method: quicksort  Memory: NNkB
@@ -709,17 +709,18 @@ rollback;
 -- Test EXPLAIN ANALYZE with both fullsort and presorted groups.
 select explain_analyze_without_memory('select * from (select * from t order by a) s order by a, b limit 70');
                                          explain_analyze_without_memory                                         
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------
+----------------------------------------------------------------------------------------------------------------
  Limit (actual rows=70 loops=1)
    ->  Incremental Sort (actual rows=70 loops=1)
          Sort Key: t.a, t.b
          Presorted Key: t.a
-         Full-sort Groups: 1 Sort Method: quicksort Memory: avg=NNkB peak=NNkB Presorted Groups: 5 Sort Methods: top-N heapsort, quicksort Memory: avg=NNkB peak=NNkB
+         Full-sort Groups: 1  Sort Method: quicksort  Average Memory: NNkB  Peak Memory: NNkB
+         Pre-sorted Groups: 5  Sort Methods: top-N heapsort, quicksort  Average Memory: NNkB  Peak Memory: NNkB
          ->  Sort (actual rows=1000 loops=1)
                Sort Key: t.a
                Sort Method: quicksort  Memory: NNkB
                ->  Seq Scan on t (actual rows=1000 loops=1)
-(9 rows)
+(10 rows)
 
 select jsonb_pretty(explain_analyze_inc_sort_nodes_without_memory('select * from (select * from t order by a) s order by a, b limit 70'));
                   jsonb_pretty                   
@@ -747,7 +748,7 @@ select jsonb_pretty(explain_analyze_inc_sort_nodes_without_memory('select * from
                  "Average Sort Space Used": "NN"+
              }                                  +
          },                                     +
-         "Presorted Groups": {                  +
+         "Pre-sorted Groups": {                 +
              "Group Count": 5,                  +
              "Sort Methods Used": [             +
                  "top-N heapsort",              +

src/test/regress/sql/incremental_sort.sql

@@ -82,7 +82,7 @@ declare
   space_key text;
 begin
   for node in select * from jsonb_array_elements(explain_analyze_inc_sort_nodes(query)) t loop
-    for group_key in select unnest(array['Full-sort Groups', 'Presorted Groups']::text[]) t loop
+    for group_key in select unnest(array['Full-sort Groups', 'Pre-sorted Groups']::text[]) t loop
       for space_key in select unnest(array['Sort Space Memory', 'Sort Space Disk']::text[]) t loop
         node := jsonb_set(node, array[group_key, space_key, 'Average Sort Space Used'], '"NN"', false);
         node := jsonb_set(node, array[group_key, space_key, 'Peak Sort Space Used'], '"NN"', false);
@@ -105,7 +105,7 @@ declare
   space_key text;
 begin
   for node in select * from jsonb_array_elements(explain_analyze_inc_sort_nodes(query)) t loop
-    for group_key in select unnest(array['Full-sort Groups', 'Presorted Groups']::text[]) t loop
+    for group_key in select unnest(array['Full-sort Groups', 'Pre-sorted Groups']::text[]) t loop
       group_stats := node->group_key;
       for space_key in select unnest(array['Sort Space Memory', 'Sort Space Disk']::text[]) t loop
         if (group_stats->space_key->'Peak Sort Space Used')::bigint < (group_stats->space_key->'Peak Sort Space Used')::bigint then