When buffering an insert to a prefix index of a variable-length column,

do not incorrectly mark the column as fixed-length.  (Bug #28138)

ibuf_entry_build(): Instead of prefix_len, pass fixed_len to
dtype_new_store_for_order_and_null_size().  Add debug assertions.

btr_index_rec_validate(): Correct a comment about prefix indexes.

rec_get_converted_size_new(), rec_convert_dtuple_to_rec_new(): Add
debug assertions and comments.

dict_col_type_assert_equal(): New debug function.

btr/btr0btr.c

@@ -2606,8 +2606,11 @@ btr_index_rec_validate(
 
 		rec_get_nth_field(rec, offsets, i, &len);
 
-		/* Note that prefix indexes are not fixed size even when
-		their type is CHAR. */
+		/* Note that if fixed_size != 0, it equals the
+		length of a fixed-size column in the clustered index.
+		A prefix index of the column is of fixed, but different
+		length.  When fixed_size == 0, prefix_len is the maximum
+		length of the prefix index column. */
 
 		if ((dict_index_get_nth_field(index, i)->prefix_len == 0
 		     && len != UNIV_SQL_NULL && fixed_size

ibuf/ibuf0ibuf.c

@@ -1440,6 +1440,9 @@ ibuf_entry_build(
 		*buf2++ = 0; /* write the compact format indicator */
 	}
 	for (i = 0; i < n_fields; i++) {
+		ulint			fixed_len;
+		const dict_field_t*	ifield;
+
 		/* We add 4 below because we have the 4 extra fields at the
 		start of an ibuf record */
 
@@ -1447,10 +1450,30 @@ ibuf_entry_build(
 		entry_field = dtuple_get_nth_field(entry, i);
 		dfield_copy(field, entry_field);
 
+		ifield = dict_index_get_nth_field(index, i);
+		/* Prefix index columns of fixed-length columns are of
+		fixed length.  However, in the function call below,
+		dfield_get_type(entry_field) contains the fixed length
+		of the column in the clustered index.  Replace it with
+		the fixed length of the secondary index column. */
+		fixed_len = ifield->fixed_len;
+
+#ifdef UNIV_DEBUG
+		if (fixed_len) {
+			/* dict_index_add_col() should guarantee these */
+			ut_ad(fixed_len <= (ulint) entry_field->type.len);
+			if (ifield->prefix_len) {
+				ut_ad(ifield->prefix_len == fixed_len);
+			} else {
+				ut_ad(fixed_len
+				      == (ulint) entry_field->type.len);
+			}
+		}
+#endif /* UNIV_DEBUG */
+
 		dtype_new_store_for_order_and_null_size(
 			buf2 + i * DATA_NEW_ORDER_NULL_TYPE_BUF_SIZE,
-			dfield_get_type(entry_field),
-			dict_index_get_nth_field(index, i)->prefix_len);
+			dfield_get_type(entry_field), fixed_len);
 	}
 
 	/* Store the type info in buf2 to field 3 of tuple */

include/dict0dict.h

@@ -92,6 +92,17 @@ dict_col_copy_type_noninline(
 /*=========================*/
 	const dict_col_t*	col,	/* in: column */
 	dtype_t*		type);	/* out: data type */
+#ifdef UNIV_DEBUG
+/*************************************************************************
+Assert that a column and a data type match. */
+UNIV_INLINE
+ibool
+dict_col_type_assert_equal(
+/*=======================*/
+					/* out: TRUE */
+	const dict_col_t*	col,	/* in: column */
+	const dtype_t*		type);	/* in: data type */
+#endif /* UNIV_DEBUG */
 /***************************************************************************
 Returns the minimum size of the column. */
 UNIV_INLINE

include/dict0dict.ic

@@ -30,6 +30,30 @@ dict_col_copy_type(
 	type->mbmaxlen = col->mbmaxlen;
 }
 
+#ifdef UNIV_DEBUG
+/*************************************************************************
+Assert that a column and a data type match. */
+UNIV_INLINE
+ibool
+dict_col_type_assert_equal(
+/*=======================*/
+					/* out: TRUE */
+	const dict_col_t*	col,	/* in: column */
+	const dtype_t*		type)	/* in: data type */
+{
+	ut_ad(col);
+	ut_ad(type);
+
+	ut_ad(col->mtype == type->mtype);
+	ut_ad(col->prtype == type->prtype);
+	ut_ad(col->len == type->len);
+	ut_ad(col->mbminlen == type->mbminlen);
+	ut_ad(col->mbmaxlen == type->mbmaxlen);
+
+	return(TRUE);
+}
+#endif /* UNIV_DEBUG */
+
 /***************************************************************************
 Returns the minimum size of the column. */
 UNIV_INLINE

rem/rem0rec.c

@@ -460,7 +460,7 @@ rec_get_converted_size_new(
 	case REC_STATUS_INFIMUM:
 	case REC_STATUS_SUPREMUM:
 		/* infimum or supremum record, 8 bytes */
-		return(size + 8); /* no extra data needed */
+		return(8); /* no extra data needed */
 	default:
 		ut_a(0);
 		return(ULINT_UNDEFINED);
@@ -476,10 +476,13 @@ rec_get_converted_size_new(
 		len = dtuple_get_nth_field(dtuple, i)->len;
 		col = dict_field_get_col(field);
 
-		ut_ad(len != UNIV_SQL_NULL || !(col->prtype & DATA_NOT_NULL));
+		ut_ad(dict_col_type_assert_equal(
+			      col, dfield_get_type(dtuple_get_nth_field(
+							   dtuple, i))));
 
 		if (len == UNIV_SQL_NULL) {
 			/* No length is stored for NULL fields. */
+			ut_ad(!(col->prtype & DATA_NOT_NULL));
 			continue;
 		}
 
@@ -487,10 +490,17 @@ rec_get_converted_size_new(
 
 		if (field->fixed_len) {
 			ut_ad(len == field->fixed_len);
+			/* dict_index_add_col() should guarantee this */
+			ut_ad(!field->prefix_len
+			      || field->fixed_len == field->prefix_len);
 		} else if (len < 128
 			   || (col->len < 256 && col->mtype != DATA_BLOB)) {
 			size++;
 		} else {
+			/* For variable-length columns, we look up the
+			maximum length from the column itself.  If this
+			is a prefix index column shorter than 256 bytes,
+			this will waste one byte. */
 			size += 2;
 		}
 		size += len;
@@ -892,6 +902,11 @@ rec_convert_dtuple_to_rec_new(
 		len = dfield_get_len(field);
 		fixed_len = dict_index_get_nth_field(index, i)->fixed_len;
 
+		ut_ad(dict_col_type_assert_equal(
+			      dict_field_get_col(dict_index_get_nth_field(
+							 index, i)),
+			      dfield_get_type(field)));
+
 		if (!(dtype_get_prtype(type) & DATA_NOT_NULL)) {
 			if (len == UNIV_SQL_NULL)
 				continue;