Fix "force_parallel_mode = regress" to work with ANALYZE + VERBOSE.

force_parallel_mode = regress is supposed to force use of a Gather node without having any impact on EXPLAIN output. But it failed to accomplish that if both ANALYZE and VERBOSE are given, because that enables per-worker output data that you wouldn't see if the Gather hadn't been inserted. Improve the logic so that we suppress the per-worker data too. This allows putting the new test case added by commit 5935917 back into the originally intended form (cf. 776a2c8, 22864f6). We can also get rid of a kluge in subselect.sql, which previously had to clean up after force_parallel_mode's failure to do what it said on the tin. Discussion: https://postgr.es/m/[email protected]

Author: tglsfdc

src/backend/commands/explain.c

@@ -695,13 +695,19 @@ ExplainPrintPlan(ExplainState *es, QueryDesc *queryDesc)
 
 /*
 * Sometimes we mark a Gather node as "invisible", which means that it's
-* not displayed in EXPLAIN output. The purpose of this is to allow
+* not to be displayed in EXPLAIN output. The purpose of this is to allow
 * running regression tests with force_parallel_mode=regress to get the
 * same results as running the same tests with force_parallel_mode=off.
+* Such marking is currently only supported on a Gather at the top of the
+* plan. We skip that node, and we must also hide per-worker detail data
+* further down in the plan tree.
 */
 ps = queryDesc->planstate;
 if (IsA(ps, GatherState) &&((Gather *) ps->plan)->invisible)
+{
 ps = outerPlanState(ps);
+es->hide_workers = true;
+}
 ExplainNode(ps, NIL, NULL, NULL, es);
 
 /*
@@ -806,6 +812,10 @@ ExplainPrintJIT(ExplainState *es, int jit_flags,
 if (!ji || ji->created_functions == 0)
 return;
 
+/* don't print per-worker info if we're supposed to hide that */
+if (for_workers && es->hide_workers)
+return;
+
 /* calculate total time */
 INSTR_TIME_SET_ZERO(total_time);
 INSTR_TIME_ADD(total_time, ji->generation_counter);
@@ -1877,7 +1887,8 @@ ExplainNode(PlanState *planstate, List *ancestors,
 show_buffer_usage(es, &planstate->instrument->bufusage);
 
 /* Show worker detail */
-if (es->analyze && es->verbose && planstate->worker_instrument)
+if (es->analyze && es->verbose && !es->hide_workers &&
+planstate->worker_instrument)
 {
 WorkerInstrumentation *w = planstate->worker_instrument;
 bool opened_group = false;
@@ -2574,6 +2585,12 @@ show_sort_info(SortState *sortstate, ExplainState *es)
 }
 }
 
+/*
+* You might think we should just skip this stanza entirely when
+* es->hide_workers is true, but then we'd get no sort-method output at
+* all. We have to make it look like worker 0's data is top-level data.
+* Currently, we only bother with that for text-format output.
+*/
 if (sortstate->shared_info != NULL)
 {
 int n;
@@ -2596,9 +2613,11 @@ show_sort_info(SortState *sortstate, ExplainState *es)
 if (es->format == EXPLAIN_FORMAT_TEXT)
 {
 appendStringInfoSpaces(es->str, es->indent * 2);
+if (n > 0 || !es->hide_workers)
+appendStringInfo(es->str, "Worker %d: ", n);
 appendStringInfo(es->str,
-"Worker %d: Sort Method: %s %s: %ldkB\n",
-n, sortMethod, spaceType, spaceUsed);
+"Sort Method: %s %s: %ldkB\n",
+sortMethod, spaceType, spaceUsed);
 }
 else
 {

src/include/commands/explain.h

@@ -46,6 +46,7 @@ typedef struct ExplainState
 List *rtable_names;	/* alias names for RTEs */
 List *deparse_cxt;	/* context list for deparsing expressions */
 Bitmapset *printed_subplans;	/* ids of SubPlans we've printed */
+bool hide_workers;	/* set if we find an invisible Gather */
 } ExplainState;
 
 /* Hook for plugins to get control in ExplainOneQuery() */

src/test/regress/expected/partition_prune.out

@@ -3163,12 +3163,12 @@ execute mt_q1(35);
 deallocate mt_q1;
 prepare mt_q2 (int) as select * from ma_test where a >= $1 order by b limit 1;
 -- Ensure output list looks sane when the MergeAppend has no subplans.
-explain (verbose, costs off) execute mt_q2 (35);
-QUERY PLAN
---------------------------------
-Limit
+explain (analyze, verbose, costs off, summary off, timing off) execute mt_q2 (35);
+QUERY PLAN
+--------------------------------------------
+Limit (actual rows=0 loops=1)
 Output: ma_test.a, ma_test.b
--> Merge Append
+-> Merge Append (actual rows=0 loops=1)
 Sort Key: ma_test.b
 Subplans Removed: 3
 (5 rows)

src/test/regress/expected/subselect.out

@@ -1166,8 +1166,6 @@ begin
 select * from (select pk,c2 from sq_limit order by c1,pk) as x limit 3
 loop
 ln := regexp_replace(ln, 'Memory: \S*', 'Memory: xxx');
--- this case might occur if force_parallel_mode is on:
-ln := regexp_replace(ln, 'Worker 0: Sort Method', 'Sort Method');
 return next ln;
 end loop;
 end;

src/test/regress/sql/partition_prune.sql

@@ -841,7 +841,7 @@ deallocate mt_q1;
 prepare mt_q2 (int) as select * from ma_test where a >= $1 order by b limit 1;
 
 -- Ensure output list looks sane when the MergeAppend has no subplans.
-explain (verbose, costs off) execute mt_q2 (35);
+explain (analyze, verbose, costs off, summary off, timing off) execute mt_q2 (35);
 
 deallocate mt_q2;
 

src/test/regress/sql/subselect.sql

@@ -631,8 +631,6 @@ begin
 select * from (select pk,c2 from sq_limit order by c1,pk) as x limit 3
 loop
 ln := regexp_replace(ln, 'Memory: \S*', 'Memory: xxx');
--- this case might occur if force_parallel_mode is on:
-ln := regexp_replace(ln, 'Worker 0: Sort Method', 'Sort Method');
 return next ln;
 end loop;
 end;