Revert "Fix accumulation of parallel worker instrumentation."

This reverts commit 2c09a5c12a66087218c7f8cba269cd3de51b9b82.  Per
further discussion, that doesn't seem to be the best possible fix.

Discussion: http://postgr.es/m/CAA4eK1LW2aFKzY3=vwvc=t-juzPPVWP2uT1bpx_MeyEqnM+p8g@mail.gmail.com

src/backend/executor/execParallel.c

@@ -819,19 +819,6 @@ ExecParallelReinitialize(PlanState *planstate,
 	/* Old workers must already be shut down */
 	Assert(pei->finished);
 
-	/* Clear the instrumentation space from the last round. */
-	if (pei->instrumentation)
-	{
-		Instrumentation *instrument;
-		SharedExecutorInstrumentation *sh_instr;
-		int			i;
-
-		sh_instr = pei->instrumentation;
-		instrument = GetInstrumentationArray(sh_instr);
-		for (i = 0; i < sh_instr->num_workers * sh_instr->num_plan_nodes; ++i)
-			InstrInit(&instrument[i], pei->planstate->state->es_instrument);
-	}
-
 	/* Force parameters we're going to pass to workers to be evaluated. */
 	ExecEvalParamExecParams(sendParams, estate);
 
@@ -953,33 +940,21 @@ ExecParallelRetrieveInstrumentation(PlanState *planstate,
 	for (n = 0; n < instrumentation->num_workers; ++n)
 		InstrAggNode(planstate->instrument, &instrument[n]);
 
-	if (!planstate->worker_instrument)
-	{
 	/*
-		 * Allocate space for the per-worker detail.
+	 * Also store the per-worker detail.
 	 *
-		 * Worker instrumentation should be allocated in the same context as
+	 * Worker instrumentation should be allocated in the same context as the
-		 * the regular instrumentation information, which is the per-query
+	 * regular instrumentation information, which is the per-query context.
-		 * context. Switch into per-query memory context.
+	 * Switch into per-query memory context.
 	 */
 	oldcontext = MemoryContextSwitchTo(planstate->state->es_query_cxt);
-		ibytes =
+	ibytes = mul_size(instrumentation->num_workers, sizeof(Instrumentation));
-			mul_size(instrumentation->num_workers, sizeof(Instrumentation));
 	planstate->worker_instrument =
 		palloc(ibytes + offsetof(WorkerInstrumentation, instrument));
 	MemoryContextSwitchTo(oldcontext);
 
-		for (n = 0; n < instrumentation->num_workers; ++n)
-			InstrInit(&planstate->worker_instrument->instrument[n],
-					  planstate->state->es_instrument);
-	}
-
 	planstate->worker_instrument->num_workers = instrumentation->num_workers;
-
+	memcpy(&planstate->worker_instrument->instrument, instrument, ibytes);
-	/* Accumulate the per-worker detail. */
-	for (n = 0; n < instrumentation->num_workers; ++n)
-		InstrAggNode(&planstate->worker_instrument->instrument[n],
-					 &instrument[n]);
 
 	/* Perform any node-type-specific work that needs to be done. */
 	switch (nodeTag(planstate))

src/test/regress/expected/select_parallel.out

@@ -465,28 +465,7 @@ select count(*) from bmscantest where a>1;
  99999
 (1 row)
 
--- test accumulation of stats for parallel node
 reset enable_seqscan;
-alter table tenk2 set (parallel_workers = 0);
-explain (analyze, timing off, summary off, costs off)
-	select count(*) from tenk1, tenk2 where tenk1.hundred > 1
-        and tenk2.thousand=0;
-                                QUERY PLAN                                
---------------------------------------------------------------------------
- Aggregate (actual rows=1 loops=1)
-   ->  Nested Loop (actual rows=98000 loops=1)
-         ->  Seq Scan on tenk2 (actual rows=10 loops=1)
-               Filter: (thousand = 0)
-               Rows Removed by Filter: 9990
-         ->  Gather (actual rows=9800 loops=10)
-               Workers Planned: 4
-               Workers Launched: 4
-               ->  Parallel Seq Scan on tenk1 (actual rows=1960 loops=50)
-                     Filter: (hundred > 1)
-                     Rows Removed by Filter: 40
-(11 rows)
-
-alter table tenk2 reset (parallel_workers);
 reset enable_indexscan;
 reset enable_hashjoin;
 reset enable_mergejoin;

src/test/regress/sql/select_parallel.sql

@@ -179,14 +179,7 @@ insert into bmscantest select r, 'fooooooooooooooooooooooooooooooooooooooooooooo
 create index i_bmtest ON bmscantest(a);
 select count(*) from bmscantest where a>1;
 
--- test accumulation of stats for parallel node
 reset enable_seqscan;
-alter table tenk2 set (parallel_workers = 0);
-explain (analyze, timing off, summary off, costs off)
-	select count(*) from tenk1, tenk2 where tenk1.hundred > 1
-        and tenk2.thousand=0;
-alter table tenk2 reset (parallel_workers);
-
 reset enable_indexscan;
 reset enable_hashjoin;
 reset enable_mergejoin;