Hi Zhzhzoo, Please find below some thoughts about the optimizer trace project * The MDEV for the optimizer trace task is https://jira.mariadb.org/browse/MDEV-6111. Let's keep it up to date with all the changes. * I think we should target MySQL-like functionality of optimizer_trace. At least, for the first milestone. We may decide to make some things better but working in a similar way to MySQL is a nice first goal. * MariaDB's optimizer trace will contain JSON and produce similar content to MySQL. However, MariaDB's optimizer is different, so one cannot expect that the JSON document will have exactly the same fields/objects/etc. (MariaDB' EXPLAIN FORMAT=JSON output doesn't match the one in MySQL, either. And in MySQL, the output varies across its versions.) * MySQL prints conditions with heavy over-quoting. Example: "original_condition": "((`A`.`a` = `B`.`a`) and ((`A`.`a` + `B`.`a`) < 10))", MariaDB has the code to print the condition without redundant quotes (see how EXPLAIN FORMAT=JSON does it). * I assume MySQL has some class for printing well-formed JSON documents. MariaDB also has one. It is in sql/my_json_writer.h, see class Json_writer. It handles printing into JSON, and also does pretty-printing. When I looked at the code last time, it did pretty-printing better than MySQL's code for EXPLAIN FORMAT=JSON did. It would be nice to use Json_writer for collecting optimizer trace output, too. (there is a caveat: Json_writer was written specifically for producing EXPLAIN FORMAT=JSON output so it may lack some features. You may need to extend it). BR Sergei -- Sergei Petrunia, Software Developer MariaDB Corporation | Skype: sergefp | Blog: http://s.petrunia.net/blog