pg_visibility: Add pg_truncate_visibility_map function.

This requires some core changes as well so that we can properly
WAL-log the truncation.  Specifically, it changes the format of the
XLOG_SMGR_TRUNCATE WAL record, so bump XLOG_PAGE_MAGIC.

Patch by me, reviewed but not fully endorsed by Andres Freund.

4 files changed, 22 insertions, 7 deletions

diff --git a/src/backend/access/rmgrdesc/smgrdesc.c b/src/backend/access/rmgrdesc/smgrdesc.c
index 0c6e5832a1c..242d79a1366 100644
--- a/src/backend/access/rmgrdesc/smgrdesc.c
+++ b/src/backend/access/rmgrdesc/smgrdesc.c
@@ -37,7 +37,8 @@ smgr_desc(StringInfo buf, XLogReaderState *record)
 		xl_smgr_truncate *xlrec = (xl_smgr_truncate *) rec;
 		char	   *path = relpathperm(xlrec->rnode, MAIN_FORKNUM);
 
-		appendStringInfo(buf, "%s to %u blocks", path, xlrec->blkno);
+		appendStringInfo(buf, "%s to %u blocks flags %d", path,
+						 xlrec->blkno, xlrec->flags);
 		pfree(path);
 	}
 }
diff --git a/src/backend/catalog/storage.c b/src/backend/catalog/storage.c
index 67f19063264..0d8311c4038 100644
--- a/src/backend/catalog/storage.c
+++ b/src/backend/catalog/storage.c
@@ -268,6 +268,7 @@ RelationTruncate(Relation rel, BlockNumber nblocks)
 
 		xlrec.blkno = nblocks;
 		xlrec.rnode = rel->rd_node;
+		xlrec.flags = SMGR_TRUNCATE_ALL;
 
 		XLogBeginInsert();
 		XLogRegisterData((char *) &xlrec, sizeof(xlrec));
@@ -522,17 +523,22 @@ smgr_redo(XLogReaderState *record)
 		 */
 		XLogFlush(lsn);
 
-		smgrtruncate(reln, MAIN_FORKNUM, xlrec->blkno);
+		if ((xlrec->flags & SMGR_TRUNCATE_HEAP) != 0)
+		{
+			smgrtruncate(reln, MAIN_FORKNUM, xlrec->blkno);
 
-		/* Also tell xlogutils.c about it */
-		XLogTruncateRelation(xlrec->rnode, MAIN_FORKNUM, xlrec->blkno);
+			/* Also tell xlogutils.c about it */
+			XLogTruncateRelation(xlrec->rnode, MAIN_FORKNUM, xlrec->blkno);
+		}
 
 		/* Truncate FSM and VM too */
 		rel = CreateFakeRelcacheEntry(xlrec->rnode);
 
-		if (smgrexists(reln, FSM_FORKNUM))
+		if ((xlrec->flags & SMGR_TRUNCATE_FSM) != 0 &&
+			smgrexists(reln, FSM_FORKNUM))
 			FreeSpaceMapTruncateRel(rel, xlrec->blkno);
-		if (smgrexists(reln, VISIBILITYMAP_FORKNUM))
+		if ((xlrec->flags & SMGR_TRUNCATE_VM) != 0 &&
+			smgrexists(reln, VISIBILITYMAP_FORKNUM))
 			visibilitymap_truncate(rel, xlrec->blkno);
 
 		FreeFakeRelcacheEntry(rel);
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index af2944c1b35..2627519ba08 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -31,7 +31,7 @@
 /*
  * Each page of XLOG file has a header like this:
  */
-#define XLOG_PAGE_MAGIC 0xD091	/* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD092	/* can be used as WAL version indicator */
 
 typedef struct XLogPageHeaderData
 {
diff --git a/src/include/catalog/storage_xlog.h b/src/include/catalog/storage_xlog.h
index 7207e8be727..500e663b5fb 100644
--- a/src/include/catalog/storage_xlog.h
+++ b/src/include/catalog/storage_xlog.h
@@ -36,10 +36,18 @@ typedef struct xl_smgr_create
 	ForkNumber	forkNum;
 } xl_smgr_create;
 
+/* flags for xl_smgr_truncate */
+#define SMGR_TRUNCATE_HEAP		0x0001
+#define SMGR_TRUNCATE_VM		0x0002
+#define SMGR_TRUNCATE_FSM		0x0004
+#define SMGR_TRUNCATE_ALL		\
+	(SMGR_TRUNCATE_HEAP|SMGR_TRUNCATE_VM|SMGR_TRUNCATE_FSM)
+
 typedef struct xl_smgr_truncate
 {
 	BlockNumber blkno;
 	RelFileNode rnode;
+	int			flags;
 } xl_smgr_truncate;
 
 extern void log_smgrcreate(RelFileNode *rnode, ForkNumber forkNum);