storage/innodb_plugin: Relax too strict assertions about prefix

indexed BLOBs for ROW_FORMAT=DYNAMIC and ROW_FORMAT_COMPRESSED tables
(Bug #52746). In these tables, the locally stored prefix of a BLOB can
be as small as 20 bytes (BTR_EXTERN_FIELD_REF_SIZE). ROW_FORMAT=REDUNDANT
and ROW_FORMAT=COMPACT store a prefix of 768 bytes (REC_MAX_INDEX_COL_LEN).

trx_undo_rec_get_col_val(): Relax the ut_ad() assertion and add a
reference to dtuple_convert_big_rec().

trx_undo_rec_get_partial_row(): Relax the ut_a() assertion that
prompted Bug #52746.

storage/innodb_plugin/ChangeLog

+2010-04-15	The InnoDB Team
+
+	* trx/trx0rec.c:
+	Fix Bug#52746 InnoDB purge thread crashed with table containing
+	prefix indexed blobs
+
 2010-03-31	The InnoDB Team
 
 	* mysql-test/innodb_bug51920.test, mysql-test/innodb_bug51920.result,

storage/innodb_plugin/trx/trx0rec.c

@@ -350,8 +350,13 @@ trx_undo_rec_get_col_val(
 
 		ut_ad(*orig_len >= BTR_EXTERN_FIELD_REF_SIZE);
 		ut_ad(*len > *orig_len);
-		ut_ad(*len >= REC_MAX_INDEX_COL_LEN
+		/* @see dtuple_convert_big_rec() */
+		ut_ad(*len >= BTR_EXTERN_FIELD_REF_SIZE * 2);
+		/* we do not have access to index->table here
+		ut_ad(dict_table_get_format(index->table) >= DICT_TF_FORMAT_ZIP
+		      || *len >= REC_MAX_INDEX_COL_LEN
 		      + BTR_EXTERN_FIELD_REF_SIZE);
+		*/
 
 		*len += UNIV_EXTERN_STORAGE_FIELD;
 		break;
@@ -1075,13 +1080,17 @@ trx_undo_rec_get_partial_row(
 			/* If the prefix of this column is indexed,
 			ensure that enough prefix is stored in the
 			undo log record. */
-			ut_a(ignore_prefix
-			     || !col->ord_part
+			if (!ignore_prefix && col->ord_part) {
+				ut_a(dfield_get_len(dfield)
+				     >= 2 * BTR_EXTERN_FIELD_REF_SIZE);
+				ut_a(dict_table_get_format(index->table)
+				     >= DICT_TF_FORMAT_ZIP
 				     || dfield_get_len(dfield)
 				     >= REC_MAX_INDEX_COL_LEN
 				     + BTR_EXTERN_FIELD_REF_SIZE);
 			}
 		}
+	}
 
 	return(ptr);
 }