Move syncscan.c to src/backend/access/common.

Since the tableam.c code needs to make use of the syncscan.c routines
itself, and since other block-oriented AMs might also want to use it one
day, it didn't make sense for it to live under src/backend/access/heap.
Reviewed-by: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/CA%2BhUKGLCnG%3DNEAByg6bk%2BCT9JZD97Y%3DAxKhh27Su9FeGWOKvDg%40mail.gmail.com

src/backend/access/common/Makefile

@@ -24,6 +24,7 @@ OBJS = \
 	reloptions.o \
 	scankey.o \
 	session.o \
+	syncscan.o \
 	toast_internals.o \
 	tupconvert.o \
 	tupdesc.o

src/backend/access/heap/syncscan.c → src/backend/access/common/syncscan.c

 /*-------------------------------------------------------------------------
  *
  * syncscan.c
- *	  heap scan synchronization support
+ *	  scan synchronization support
  *
  * When multiple backends run a sequential scan on the same table, we try
  * to keep them synchronized to reduce the overall I/O needed.  The goal is
@@ -40,13 +40,13 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  src/backend/access/heap/syncscan.c
+ *	  src/backend/access/common/syncscan.c
  *
  *-------------------------------------------------------------------------
  */
 #include "postgres.h"
 
-#include "access/heapam.h"
+#include "access/syncscan.h"
 #include "miscadmin.h"
 #include "storage/lwlock.h"
 #include "storage/shmem.h"

src/backend/access/heap/Makefile

@@ -20,7 +20,6 @@ OBJS = \
 	hio.o \
 	pruneheap.o \
 	rewriteheap.o \
-	syncscan.o \
 	vacuumlazy.o \
 	visibilitymap.o
 

src/backend/access/heap/heapam.c

@@ -41,6 +41,7 @@
 #include "access/parallel.h"
 #include "access/relscan.h"
 #include "access/subtrans.h"
+#include "access/syncscan.h"
 #include "access/sysattr.h"
 #include "access/tableam.h"
 #include "access/transam.h"

src/backend/access/heap/heapam_handler.c

@@ -24,6 +24,7 @@
 #include "access/heaptoast.h"
 #include "access/multixact.h"
 #include "access/rewriteheap.h"
+#include "access/syncscan.h"
 #include "access/tableam.h"
 #include "access/tsmapi.h"
 #include "access/xact.h"

src/backend/access/table/tableam.c

@@ -21,7 +21,7 @@
 
 #include <math.h>
 
-#include "access/heapam.h"		/* for ss_* */
+#include "access/syncscan.h"
 #include "access/tableam.h"
 #include "access/xact.h"
 #include "optimizer/plancat.h"

src/backend/storage/ipc/ipci.c

@@ -20,6 +20,7 @@
 #include "access/multixact.h"
 #include "access/nbtree.h"
 #include "access/subtrans.h"
+#include "access/syncscan.h"
 #include "access/twophase.h"
 #include "commands/async.h"
 #include "miscadmin.h"

src/include/access/heapam.h

@@ -182,12 +182,6 @@ extern void heap_page_prune_execute(Buffer buffer,
 									OffsetNumber *nowunused, int nunused);
 extern void heap_get_root_tuples(Page page, OffsetNumber *root_offsets);
 
-/* in heap/syncscan.c */
-extern void ss_report_location(Relation rel, BlockNumber location);
-extern BlockNumber ss_get_location(Relation rel, BlockNumber relnblocks);
-extern void SyncScanShmemInit(void);
-extern Size SyncScanShmemSize(void);
-
 /* in heap/vacuumlazy.c */
 struct VacuumParams;
 extern void heap_vacuum_rel(Relation onerel,

src/include/access/syncscan.h

+/*-------------------------------------------------------------------------
+ *
+ * syncscan.h
+ *    POSTGRES synchronous scan support functions.
+ *
+ *
+ * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/access/syncscan.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef SYNCSCAN_H
+#define SYNCSCAN_H
+
+#include "storage/block.h"
+#include "utils/relcache.h"
+
+extern void ss_report_location(Relation rel, BlockNumber location);
+extern BlockNumber ss_get_location(Relation rel, BlockNumber relnblocks);
+extern void SyncScanShmemInit(void);
+extern Size SyncScanShmemSize(void);
+
+#endif