Emit nbtree vacuum cycle id in nbtree xlog through FPIs

This fixes the PostgreSQL side of neondatabase/neon#9929.

src/backend/access/nbtree/nbtinsert.c

@@ -1978,7 +1978,18 @@ _bt_split(Relation rel, BTScanInsert itup_key, Buffer buf, Buffer cbuf,
 		XLogBeginInsert();
 		XLogRegisterData((char *) &xlrec, SizeOfBtreeSplit);
 
-		XLogRegisterBuffer(0, buf, REGBUF_STANDARD);
+		/*
+		 * NEON: If we split during a btree vacuum cycle, and the new right
+		 * sibling is located before the original page in the relation, then
+		 * we have to include the cycle ID in the WAL record. The easiest
+		 * method to do that is to force an image, which happens to be
+		 * relatively cheap, as the data already contained in the record is
+		 * enough to populate the new right page.
+		 */
+		if (origpagenumber < rightpagenumber || lopaque->btpo_cycleid == 0)
+			XLogRegisterBuffer(0, buf, REGBUF_STANDARD);
+		else
+			XLogRegisterBuffer(0, buf, REGBUF_FORCE_IMAGE | REGBUF_STANDARD);
 		XLogRegisterBuffer(1, rbuf, REGBUF_WILL_INIT);
 		/* Log original right sibling, since we've changed its prev-pointer */
 		if (!isrightmost)