Remove dedicated B-tree root-split record types.

Since commit 40dae7ec53, which changed the way b-tree page splitting
works, there has been no difference in the handling of root, and non-root
split WAL records. We don't need to distinguish them anymore

If you're worried about the loss of debugging information, note that
usually a root split record will normally be followed by a WAL record to
create the new root page. The root page will also have the BTP_ROOT flag
set on the page itself, and there is a pointer to it from the metapage.

Author: Aleksander Alekseev
Discussion: https://www.postgresql.org/message-id/20170406122116.GA11081@e733.localdomain

src/backend/access/nbtree/nbtinsert.c

@@ -980,7 +980,6 @@ _bt_split(Relation rel, Buffer buf, Buffer cbuf, OffsetNumber firstright,
 				rightoff;
 	OffsetNumber maxoff;
 	OffsetNumber i;
-	bool		isroot;
 	bool		isleaf;
 
 	/* Acquire a new page to split into */
@@ -1019,7 +1018,6 @@ _bt_split(Relation rel, Buffer buf, Buffer cbuf, OffsetNumber firstright,
 	lopaque = (BTPageOpaque) PageGetSpecialPointer(leftpage);
 	ropaque = (BTPageOpaque) PageGetSpecialPointer(rightpage);
 
-	isroot = P_ISROOT(oopaque);
 	isleaf = P_ISLEAF(oopaque);
 
 	/* if we're splitting this page, it won't be the root when we're done */
@@ -1330,11 +1328,7 @@ _bt_split(Relation rel, Buffer buf, Buffer cbuf, OffsetNumber firstright,
 							(char *) rightpage + ((PageHeader) rightpage)->pd_upper,
 							((PageHeader) rightpage)->pd_special - ((PageHeader) rightpage)->pd_upper);
 
-		if (isroot)
-			xlinfo = newitemonleft ? XLOG_BTREE_SPLIT_L_ROOT : XLOG_BTREE_SPLIT_R_ROOT;
-		else
-			xlinfo = newitemonleft ? XLOG_BTREE_SPLIT_L : XLOG_BTREE_SPLIT_R;
-
+		xlinfo = newitemonleft ? XLOG_BTREE_SPLIT_L : XLOG_BTREE_SPLIT_R;
 		recptr = XLogInsert(RM_BTREE_ID, xlinfo);
 
 		PageSetLSN(origpage, recptr);

src/backend/access/nbtree/nbtxlog.c

@@ -193,7 +193,7 @@ btree_xlog_insert(bool isleaf, bool ismeta, XLogReaderState *record)
 }
 
 static void
-btree_xlog_split(bool onleft, bool isroot, XLogReaderState *record)
+btree_xlog_split(bool onleft, XLogReaderState *record)
 {
 	XLogRecPtr	lsn = record->EndRecPtr;
 	xl_btree_split *xlrec = (xl_btree_split *) XLogRecGetData(record);
@@ -996,16 +996,10 @@ btree_redo(XLogReaderState *record)
 			btree_xlog_insert(false, true, record);
 			break;
 		case XLOG_BTREE_SPLIT_L:
-			btree_xlog_split(true, false, record);
+			btree_xlog_split(true, record);
 			break;
 		case XLOG_BTREE_SPLIT_R:
-			btree_xlog_split(false, false, record);
-			break;
-		case XLOG_BTREE_SPLIT_L_ROOT:
-			btree_xlog_split(true, true, record);
-			break;
-		case XLOG_BTREE_SPLIT_R_ROOT:
-			btree_xlog_split(false, true, record);
+			btree_xlog_split(false, record);
 			break;
 		case XLOG_BTREE_VACUUM:
 			btree_xlog_vacuum(record);

src/backend/access/rmgrdesc/nbtdesc.c

@@ -35,8 +35,6 @@ btree_desc(StringInfo buf, XLogReaderState *record)
 			}
 		case XLOG_BTREE_SPLIT_L:
 		case XLOG_BTREE_SPLIT_R:
-		case XLOG_BTREE_SPLIT_L_ROOT:
-		case XLOG_BTREE_SPLIT_R_ROOT:
 			{
 				xl_btree_split *xlrec = (xl_btree_split *) rec;
 
@@ -121,12 +119,6 @@ btree_identify(uint8 info)
 		case XLOG_BTREE_SPLIT_R:
 			id = "SPLIT_R";
 			break;
-		case XLOG_BTREE_SPLIT_L_ROOT:
-			id = "SPLIT_L_ROOT";
-			break;
-		case XLOG_BTREE_SPLIT_R_ROOT:
-			id = "SPLIT_R_ROOT";
-			break;
 		case XLOG_BTREE_VACUUM:
 			id = "VACUUM";
 			break;

src/include/access/nbtxlog.h

@@ -28,8 +28,7 @@
 #define XLOG_BTREE_INSERT_META	0x20	/* same, plus update metapage */
 #define XLOG_BTREE_SPLIT_L		0x30	/* add index tuple with split */
 #define XLOG_BTREE_SPLIT_R		0x40	/* as above, new item on right */
-#define XLOG_BTREE_SPLIT_L_ROOT 0x50	/* add tuple with split of root */
-#define XLOG_BTREE_SPLIT_R_ROOT 0x60	/* as above, new item on right */
+/* 0x50 and 0x60 are unused */
 #define XLOG_BTREE_DELETE		0x70	/* delete leaf index tuples for a page */
 #define XLOG_BTREE_UNLINK_PAGE	0x80	/* delete a half-dead page */
 #define XLOG_BTREE_UNLINK_PAGE_META 0x90	/* same, and update metapage */