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, 13 insertions, 1 deletions

diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index 07cd20ac504..064a0509c4d 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -1585,6 +1585,7 @@ typedef struct ForeignScanState
 {
 	ScanState	ss;				/* its first field is NodeTag */
 	List	   *fdw_recheck_quals;	/* original quals not in ss.ps.qual */
+	Size		pscan_len;		/* size of parallel coordination information */
 	/* use struct pointer to avoid including fdwapi.h here */
 	struct FdwRoutine *fdwroutine;
 	void	   *fdw_state;		/* foreign-data wrapper can keep state here */
@@ -1603,6 +1604,8 @@ typedef struct ForeignScanState
  * the BeginCustomScan method.
  * ----------------
  */
+struct ParallelContext;			/* avoid including parallel.h here */
+struct shm_toc;					/* avoid including shm_toc.h here */
 struct ExplainState;			/* avoid including explain.h here */
 struct CustomScanState;
 
@@ -1619,7 +1622,15 @@ typedef struct CustomExecMethods
 	void		(*ReScanCustomScan) (struct CustomScanState *node);
 	void		(*MarkPosCustomScan) (struct CustomScanState *node);
 	void		(*RestrPosCustomScan) (struct CustomScanState *node);
-
+	/* Optional: parallel execution support */
+	Size		(*EstimateDSMCustomScan) (struct CustomScanState *node,
+											   struct ParallelContext *pcxt);
+	void		(*InitializeDSMCustomScan) (struct CustomScanState *node,
+												struct ParallelContext *pcxt,
+														void *coordinate);
+	void		(*InitializeWorkerCustomScan) (struct CustomScanState *node,
+														 struct shm_toc *toc,
+														   void *coordinate);
 	/* Optional: print additional information in EXPLAIN */
 	void		(*ExplainCustomScan) (struct CustomScanState *node,
 												  List *ancestors,
@@ -1631,6 +1642,7 @@ typedef struct CustomScanState
 	ScanState	ss;
 	uint32		flags;			/* mask of CUSTOMPATH_* flags, see relation.h */
 	List	   *custom_ps;		/* list of child PlanState nodes, if any */
+	Size		pscan_len;		/* size of parallel coordination information */
 	const CustomExecMethods *methods;
 } CustomScanState;