Use outerplan start as hash node start

Makefile

@@ -19,7 +19,7 @@ OBJS = \
 	src/pg_tracing_span.o
 
 REGRESSCHECKS = setup utility select extended insert trigger sample \
-				planstate planstate_bitmap \
+				planstate planstate_bitmap planstate_hash \
 				parallel subxact full_buffer \
 				nested wal cleanup
 REGRESSCHECKS_OPTS = --no-locale --encoding=UTF8 --temp-config pg_tracing.conf

expected/planstate_hash.out

@@ -0,0 +1,60 @@
+/*dddbs='postgres.db',traceparent='00-00000000000000000000000000000001-0000000000000001-01'*/ select count(*) from pg_tracing_test r join pg_tracing_test s using (a);
+ count 
+-------
+ 10000
+(1 row)
+
+SELECT span_operation, deparse_info, parameters, lvl from peek_ordered_spans where trace_id='00000000000000000000000000000001';
+                              span_operation                              |    deparse_info    | parameters | lvl 
+--------------------------------------------------------------------------+--------------------+------------+-----
+ select count(*) from pg_tracing_test r join pg_tracing_test s using (a); |                    |            |   1
+ Planner                                                                  |                    |            |   2
+ ExecutorRun                                                              |                    |            |   2
+ Aggregate                                                                |                    |            |   3
+ Hash Join                                                                | Hash Cond: (a = a) |            |   4
+ SeqScan on pg_tracing_test r                                             |                    |            |   5
+ Hash                                                                     |                    |            |   5
+ SeqScan on pg_tracing_test s                                             |                    |            |   6
+(8 rows)
+
+-- +-----------------------------------------+
+-- | A: HashJoin                             |
+-- ++-----------------+----------------------+
+--  | B: SeqScan      |
+--  +-----------------+
+--    +--------------------+
+--    | C: Hash            |
+--    +--------------------+
+--    | D: SeqScan   |
+--    +--------------+
+SELECT span_id AS span_a_id,
+        get_epoch(span_start) as span_a_start,
+        get_epoch(span_end) as span_a_end
+		from pg_tracing_peek_spans
+        where trace_id='00000000000000000000000000000001' AND span_operation='Hash Join' \gset
+SELECT span_id AS span_b_id,
+        get_epoch(span_start) as span_b_start,
+        get_epoch(span_end) as span_b_end
+		from pg_tracing_peek_spans
+        where parent_id =:'span_a_id' and span_operation='SeqScan on pg_tracing_test r' \gset
+SELECT span_id AS span_c_id,
+        get_epoch(span_start) as span_c_start,
+        get_epoch(span_end) as span_c_end
+		from pg_tracing_peek_spans
+        where parent_id =:'span_a_id' and span_operation='Hash' \gset
+SELECT span_id AS span_d_id,
+        get_epoch(span_start) as span_d_start,
+        get_epoch(span_end) as span_d_end
+		from pg_tracing_peek_spans
+        where parent_id =:'span_c_id' and span_operation='SeqScan on pg_tracing_test s' \gset
+SELECT :span_a_end >= :span_c_end as root_ends_last,
+       :span_c_start >= :span_b_start as hash_start_after_seqscan,
+       :span_c_start = :span_d_start as hash_start_same_as_child_seqscan,
+       :span_d_end <= :span_c_end as nested_seq_scan_end_before_parent;
+ root_ends_last | hash_start_after_seqscan | hash_start_same_as_child_seqscan | nested_seq_scan_end_before_parent 
+----------------+--------------------------+----------------------------------+-----------------------------------
+ t              | t                        | t                                | t
+(1 row)
+
+-- Clean created spans
+CALL clean_spans();

sql/planstate_hash.sql

@@ -0,0 +1,42 @@
+/*dddbs='postgres.db',traceparent='00-00000000000000000000000000000001-0000000000000001-01'*/ select count(*) from pg_tracing_test r join pg_tracing_test s using (a);
+SELECT span_operation, deparse_info, parameters, lvl from peek_ordered_spans where trace_id='00000000000000000000000000000001';
+
+-- +-----------------------------------------+
+-- | A: HashJoin                             |
+-- ++-----------------+----------------------+
+--  | B: SeqScan      |
+--  +-----------------+
+--    +--------------------+
+--    | C: Hash            |
+--    +--------------------+
+--    | D: SeqScan   |
+--    +--------------+
+
+SELECT span_id AS span_a_id,
+        get_epoch(span_start) as span_a_start,
+        get_epoch(span_end) as span_a_end
+		from pg_tracing_peek_spans
+        where trace_id='00000000000000000000000000000001' AND span_operation='Hash Join' \gset
+SELECT span_id AS span_b_id,
+        get_epoch(span_start) as span_b_start,
+        get_epoch(span_end) as span_b_end
+		from pg_tracing_peek_spans
+        where parent_id =:'span_a_id' and span_operation='SeqScan on pg_tracing_test r' \gset
+SELECT span_id AS span_c_id,
+        get_epoch(span_start) as span_c_start,
+        get_epoch(span_end) as span_c_end
+		from pg_tracing_peek_spans
+        where parent_id =:'span_a_id' and span_operation='Hash' \gset
+SELECT span_id AS span_d_id,
+        get_epoch(span_start) as span_d_start,
+        get_epoch(span_end) as span_d_end
+		from pg_tracing_peek_spans
+        where parent_id =:'span_c_id' and span_operation='SeqScan on pg_tracing_test s' \gset
+
+SELECT :span_a_end >= :span_c_end as root_ends_last,
+       :span_c_start >= :span_b_start as hash_start_after_seqscan,
+       :span_c_start = :span_d_start as hash_start_same_as_child_seqscan,
+       :span_d_end <= :span_c_end as nested_seq_scan_end_before_parent;
+
+-- Clean created spans
+CALL clean_spans();

src/pg_tracing_planstate.c

@@ -68,7 +68,8 @@ drop_traced_planstate(int exec_nested_level)
 }
 
 /*
- * If spans from planstate is requested, we override planstate's ExecProcNode's pointer with this function. It will track the time of the first node call needed to place the planstate span.
+ * If spans from planstate is requested, we override planstate's ExecProcNode's pointer with this function.
+ * It will track the time of the first node call needed to place the planstate span.
  */
 static TupleTableSlot *
 ExecProcNodeFirstPgTracing(PlanState *node)
@@ -388,17 +389,20 @@ generate_span_from_planstate(PlanState *planstate, planstateTraceContext * plans
 	switch (nodeTag(planstate->plan))
 	{
 		case T_BitmapIndexScan:
-		case T_Hash:
 		case T_BitmapAnd:
 		case T_BitmapOr:
 
 			/*
 			 * Those nodes won't go through ExecProcNode so we won't have
-			 * their start. Fallback to the parent start. TODO: Use the child
-			 * start as a fallback instead
+			 * their start. Fallback to the parent start.
 			 */
 			span_start = fallback_start;
 			break;
+		case T_Hash:
+			/* For hash node, use the child's start */
+			traced_planstate = get_traced_planstate(outerPlanState(planstate));
+			span_start = traced_planstate->node_start;
+			break;
 		default:
 			traced_planstate = get_traced_planstate(planstate);
 			/* TODO: better fallback if planstate is not found */