Allow parallel custom and foreign scans.

This patch doesn't put the new infrastructure to use anywhere, and
indeed it's not clear how it could ever be used for something like
postgres_fdw which has to send an SQL query and wait for a reply,
but there might be FDWs or custom scan providers that are CPU-bound,
so let's give them a way to join club parallel.

KaiGai Kohei, reviewed by me.

1 files changed, 45 insertions, 0 deletions

diff --git a/src/backend/executor/nodeCustom.c b/src/backend/executor/nodeCustom.c
index 640289e2773..322abca282a 100644
--- a/src/backend/executor/nodeCustom.c
+++ b/src/backend/executor/nodeCustom.c
@@ -10,6 +10,7 @@
  */
 #include "postgres.h"
 
+#include "access/parallel.h"
 #include "executor/executor.h"
 #include "executor/nodeCustom.h"
 #include "nodes/execnodes.h"
@@ -159,3 +160,47 @@ ExecCustomRestrPos(CustomScanState *node)
 						node->methods->CustomName)));
 	node->methods->RestrPosCustomScan(node);
 }
+
+void
+ExecCustomScanEstimate(CustomScanState *node, ParallelContext *pcxt)
+{
+	const CustomExecMethods *methods = node->methods;
+
+	if (methods->EstimateDSMCustomScan)
+	{
+		node->pscan_len = methods->EstimateDSMCustomScan(node, pcxt);
+		shm_toc_estimate_chunk(&pcxt->estimator, node->pscan_len);
+		shm_toc_estimate_keys(&pcxt->estimator, 1);
+	}
+}
+
+void
+ExecCustomScanInitializeDSM(CustomScanState *node, ParallelContext *pcxt)
+{
+	const CustomExecMethods *methods = node->methods;
+
+	if (methods->InitializeDSMCustomScan)
+	{
+		int			plan_node_id = node->ss.ps.plan->plan_node_id;
+		void	   *coordinate;
+
+		coordinate = shm_toc_allocate(pcxt->toc, node->pscan_len);
+		methods->InitializeDSMCustomScan(node, pcxt, coordinate);
+		shm_toc_insert(pcxt->toc, plan_node_id, coordinate);
+	}
+}
+
+void
+ExecCustomScanInitializeWorker(CustomScanState *node, shm_toc *toc)
+{
+	const CustomExecMethods *methods = node->methods;
+
+	if (methods->InitializeWorkerCustomScan)
+	{
+		int			plan_node_id = node->ss.ps.plan->plan_node_id;
+		void	   *coordinate;
+
+		coordinate = shm_toc_lookup(toc, plan_node_id);
+		methods->InitializeWorkerCustomScan(node, toc, coordinate);
+	}
+}