ibuf_entry_build(): Write prefix_len to the insert buffer instead of type->len

when prefix_len is specified.  Otherwise, btr_page_reorganize() during
insert buffer merge would fail on ROW_FORMAT=COMPACT tables.  (Bug #21638)

ibuf/ibuf0ibuf.c

@@ -1365,8 +1365,8 @@ ibuf_entry_build(
 				index tree; NOTE that the original entry
 				must be kept because we copy pointers to its
 				fields */
+	dict_index_t*	index,	/* in: non-clustered index */
 	dtuple_t*	entry,	/* in: entry for a non-clustered index */
-	ibool		comp,	/* in: flag: TRUE=compact record format */
 	ulint		space,	/* in: space id */
 	ulint		page_no,/* in: index page number where entry should
 				be inserted */
@@ -1430,13 +1430,12 @@ ibuf_entry_build(
 
 	dfield_set_data(field, buf, 4);
 
-	ut_ad(comp == 0 || comp == 1);
 	/* Store the type info in buf2, and add the fields from entry to
 	tuple */
 	buf2 = mem_heap_alloc(heap, n_fields
 			      * DATA_NEW_ORDER_NULL_TYPE_BUF_SIZE
-			      + comp);
-	if (comp) {
+			      + dict_table_is_comp(index->table));
+	if (dict_table_is_comp(index->table)) {
 		*buf2++ = 0; /* write the compact format indicator */
 	}
 	for (i = 0; i < n_fields; i++) {
@@ -1449,20 +1448,21 @@ ibuf_entry_build(
 
 		dtype_new_store_for_order_and_null_size
 			(buf2 + i * DATA_NEW_ORDER_NULL_TYPE_BUF_SIZE,
-			 dfield_get_type(entry_field));
+			 dfield_get_type(entry_field),
+			 dict_index_get_nth_field(index, i)->prefix_len);
 	}
 
 	/* Store the type info in buf2 to field 3 of tuple */
 
 	field = dtuple_get_nth_field(tuple, 3);
 
-	if (comp) {
+	if (dict_table_is_comp(index->table)) {
 		buf2--;
 	}
 
 	dfield_set_data(field, buf2, n_fields
 			* DATA_NEW_ORDER_NULL_TYPE_BUF_SIZE
-			+ comp);
+			+ dict_table_is_comp(index->table));
 	/* Set all the types in the new tuple binary */
 
 	dtuple_set_types_binary(tuple, n_fields + 4);
@@ -2605,8 +2605,7 @@ ibuf_insert_low(
 	the first fields and the type information for other fields, and which
 	will be inserted to the insert buffer. */
 
-	ibuf_entry = ibuf_entry_build(entry, dict_table_is_comp(index->table),
-				      space, page_no, heap);
+	ibuf_entry = ibuf_entry_build(index, entry, space, page_no, heap);
 
 	/* Open a cursor to the insert buffer tree to calculate if we can add
 	the new entry to it without exceeding the free space limit for the

include/data0type.h

@@ -376,7 +376,9 @@ dtype_new_store_for_order_and_null_size(
 	byte*		buf,	/* in: buffer for
 				DATA_NEW_ORDER_NULL_TYPE_BUF_SIZE
 				bytes where we store the info */
-	dtype_t*	type);	/* in: type struct */
+	dtype_t*	type,	/* in: type struct */
+	ulint		prefix_len);/* in: prefix length to
+				replace type->len, or 0 */
 /**************************************************************************
 Reads to a type the stored information which determines its alphabetical
 ordering and the storage size of an SQL NULL value. This is the 4.1.x storage

include/data0type.ic

@@ -244,11 +244,14 @@ dtype_new_store_for_order_and_null_size(
 	byte*		buf,	/* in: buffer for
 				DATA_NEW_ORDER_NULL_TYPE_BUF_SIZE
 				bytes where we store the info */
-	dtype_t*	type)	/* in: type struct */
+	dtype_t*	type,	/* in: type struct */
+	ulint		prefix_len)/* in: prefix length to
+				replace type->len, or 0 */
 {
 #if 6 != DATA_NEW_ORDER_NULL_TYPE_BUF_SIZE
 #error "6 != DATA_NEW_ORDER_NULL_TYPE_BUF_SIZE"
 #endif
+	ulint	len;
 
 	buf[0] = (byte)(type->mtype & 0xFFUL);
 
@@ -263,7 +266,9 @@ dtype_new_store_for_order_and_null_size(
 
 	buf[1] = (byte)(type->prtype & 0xFFUL);
 
-	mach_write_to_2(buf + 2, type->len & 0xFFFFUL);
+	len = prefix_len ? prefix_len : type->len;
+
+	mach_write_to_2(buf + 2, len & 0xFFFFUL);
 
 	ut_ad(dtype_get_charset_coll(type->prtype) < 256);
 	mach_write_to_2(buf + 4, dtype_get_charset_coll(type->prtype));