MDEV-19783: Add more assertions

btr_page_get_split_rec_to_left(): Assert that in the leftmost leaf page,
the metadata record exists if and only if index->is_instant().

page_validate(): Correct the wording of a message.

rec_init_offsets(): Assert that whenever a record is in "instant ALTER"
format, index->is_instant() must hold.

storage/innobase/btr/btr0btr.cc

@@ -2062,6 +2062,14 @@ rec_t* btr_page_get_split_rec_to_left(const btr_cur_t* cursor)
 		return NULL;
 	}
 
+	/* The metadata record must be present in the leftmost leaf page
+	of the clustered index, if and only if index->is_instant(). */
+	ut_ad(!page_is_leaf(page) || page_has_prev(page)
+	      || cursor->index->is_instant()
+	      == rec_is_metadata(page_rec_get_next_const(
+					 page_get_infimum_rec(page)),
+				 cursor->index));
+
 	const rec_t* infimum = page_get_infimum_rec(page);
 
 	/* If the convergence is in the middle of a page, include also
@@ -2783,7 +2791,7 @@ btr_page_split_and_insert(
 	ulint		n_iterations = 0;
 	ulint		n_uniq;
 
-	if (dict_index_is_spatial(cursor->index)) {
+	if (cursor->index->is_spatial()) {
 		/* Split rtree page and update parent */
 		return(rtr_page_split_and_insert(flags, cursor, offsets, heap,
 						 tuple, n_ext, mtr));

storage/innobase/page/page0page.cc

@@ -839,7 +839,8 @@ page_copy_rec_list_start(
 	const bool is_leaf = page_rec_is_leaf(rec);
 
 	/* Copy records from the original page to the new page */
-	if (dict_index_is_spatial(index)) {
+	if (index->is_spatial()) {
+		ut_ad(!index->is_instant());
 		ulint		max_to_move = page_get_n_recs(
 						buf_block_get_frame(block));
 		heap = mem_heap_create(256);
@@ -2535,7 +2536,7 @@ bool page_validate(const page_t* page, const dict_index_t* index)
 			     & REC_INFO_MIN_REC_FLAG)) {
 				if (page_has_prev(page)) {
 					ib::error() << "REC_INFO_MIN_REC_FLAG "
-						"is set in on non-left page";
+						"is set on non-left page";
 					ret = false;
 				} else if (!page_is_leaf(page)) {
 					/* leftmost node pointer page */

storage/innobase/rem/rem0rec.cc

@@ -600,6 +600,7 @@ rec_init_offsets(
 			break;
 		case REC_STATUS_COLUMNS_ADDED:
 			ut_ad(leaf);
+			ut_ad(index->is_instant());
 			rec_init_offsets_comp_ordinary(rec, index, offsets,
 						       index->n_core_fields,
 						       NULL,
@@ -741,6 +742,8 @@ rec_init_offsets(
 		}
 
 		if (i < rec_offs_n_fields(offsets)) {
+			ut_ad(index->is_instant());
+
 			offs = (rec_offs_base(offsets)[i] & REC_OFFS_MASK)
 				| REC_OFFS_DEFAULT;