MySQL 5.7.5-labsのQuery Rewrite Plugin

Query Rewrite pluginの一番ベーシックな使い方はこちら。
The Query Rewrite Plugins | MySQL Server Blog

MySQL 5.7.5-labsに$basedir/lib/plugin/install_rewriter_plugin.sqlを食わせてやれば取り敢えず有効になる。MySQL 5.7.5-m15にはこのプラグインは存在しないので注意。

$ mysql57 < install_rewriter_plugin.sql

mysql57> SELECT @@version;
+------------------------+
| @@version              |
+------------------------+
| 5.7.5-labs-preview-log |
+------------------------+
1 row in set (0.00 sec)

mysql57> show plugins;
+----------------------------+--------+--------------------------+-------------+---------+
| Name                       | Status | Type                     | Library     | License |
+----------------------------+--------+--------------------------+-------------+---------+
..
| Rewriter                   | ACTIVE | QUERY REWRITE POST PARSE | rewriter.so | GPL     |
+----------------------------+--------+--------------------------+-------------+---------+
43 rows in set (0.00 sec)

mysql57> show databases like 'query_rewrite';
+--------------------------+
| Database (query_rewrite) |
+--------------------------+
| query_rewrite            |
+--------------------------+
1 row in set (0.00 sec)

mysql57> show tables;
+-------------------------+
| Tables_in_query_rewrite |
+-------------------------+
| rewrite_rules           |
+-------------------------+
1 row in set (0.00 sec)

このquery_rewrite.rewrite_rulesにクエリー書き換えのルールを記述していく感じ。
記述したら、query_rewrite.flush_rewrite_rulesを呼んで更新してやる(FLUSH PRIVILEGESみたいな感じだ)

mysql57> INSERT INTO query_rewrite.rewrite_rules (pattern, replacement) VALUES ('INSERT INTO t1 VALUES (?)', 'INSERT INTO t2 VALUES (? + 1)');
Query OK, 1 row affected (0.01 sec)

mysql57> SELECT * FROM query_rewrite.rewrite_rules;
+---------------------------+------------------+-------------------------------+---------+---------+
| pattern                   | pattern_database | replacement                   | enabled | message |
+---------------------------+------------------+-------------------------------+---------+---------+
| INSERT INTO t1 VALUES (?) | NULL             | INSERT INTO t2 VALUES (? + 1) | Y       | NULL    |
+---------------------------+------------------+-------------------------------+---------+---------+
1 row in set (0.00 sec)

mysql57> CALL query_rewrite.flush_rewrite_rules();
Query OK, 1 row affected (0.01 sec)

mysql57> SELECT * FROM query_rewrite.rewrite_rules;
+---------------------------+------------------+-------------------------------+---------+--------------------------------------------------+
| pattern                   | pattern_database | replacement                   | enabled | message                                          |
+---------------------------+------------------+-------------------------------+---------+--------------------------------------------------+
| INSERT INTO t1 VALUES (?) | NULL             | INSERT INTO t2 VALUES (? + 1) | N       | Parse error in pattern: >>No database selected<< |
+---------------------------+------------------+-------------------------------+---------+--------------------------------------------------+
1 row in set (0.00 sec)

あれ、なんか怒られた。 "No database selected" なので、pattern_databaseがNULLなのがいけないのか…ってテーブル名を指定しない時はNULLでも大丈夫ぽい流れが冒頭のブログには書いてあった(´･ω･｀)

mysql57> UPDATE query_rewrite.rewrite_rules SET pattern_database= 'd1', enabled= 'Y';
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql57> SELECT * FROM query_rewrite.rewrite_rules;
+---------------------------+------------------+-------------------------------+---------+--------------------------------------------------+
| pattern                   | pattern_database | replacement                   | enabled | message                                          |
+---------------------------+------------------+-------------------------------+---------+--------------------------------------------------+
| INSERT INTO t1 VALUES (?) | d1               | INSERT INTO t2 VALUES (? + 1) | Y       | Parse error in pattern: >>No database selected<< |
+---------------------------+------------------+-------------------------------+---------+--------------------------------------------------+
1 row in set (0.00 sec)

enabledは自分で'Y'に戻さないと、次にflush_rewrite_rulesを呼んでもそもそもFLUSHしようとしてくれなくなる(はまった)

mysql57> CALL query_rewrite.flush_rewrite_rules();
Query OK, 1 row affected (0.00 sec)

mysql57> SELECT * FROM query_rewrite.rewrite_rules;
+---------------------------+------------------+-------------------------------+---------+---------------------------------+
| pattern                   | pattern_database | replacement                   | enabled | message                         |
+---------------------------+------------------+-------------------------------+---------+---------------------------------+
| INSERT INTO t1 VALUES (?) | d1               | INSERT INTO t2 VALUES (? + 1) | N       | Pattern not a select statement. |
+---------------------------+------------------+-------------------------------+---------+---------------------------------+
1 row in set (0.00 sec)

(´･ω･｀) SELECTステートメントしか食ってくれないようなことを言っている。かなしい。

mysql57> DELETE FROM query_rewrite.rewrite_rules;
Query OK, 1 row affected (0.00 sec)

mysql57> INSERT INTO query_rewrite.rewrite_rules (pattern, pattern_database, replacement) VALUES ('SELECT * FROM t1', 'd1', 'SELECT * FROM t1 LIMIT 1');
Query OK, 1 row affected (0.00 sec)

mysql57> SELECT * FROM query_rewrite.rewrite_rules;
+------------------+------------------+--------------------------+---------+---------+
| pattern          | pattern_database | replacement              | enabled | message |
+------------------+------------------+--------------------------+---------+---------+
| SELECT * FROM t1 | d1               | SELECT * FROM t1 LIMIT 1 | Y       | NULL    |
+------------------+------------------+--------------------------+---------+---------+
1 row in set (0.00 sec)

mysql57> CALL query_rewrite.flush_rewrite_rules();
Query OK, 1 row affected (0.01 sec)

mysql57> SELECT * FROM query_rewrite.rewrite_rules;
+------------------+------------------+--------------------------+---------+---------+
| pattern          | pattern_database | replacement              | enabled | message |
+------------------+------------------+--------------------------+---------+---------+
| SELECT * FROM t1 | d1               | SELECT * FROM t1 LIMIT 1 | Y       | NULL    |
+------------------+------------------+--------------------------+---------+---------+
1 row in set (0.00 sec)

という訳で、d1.t1のテーブルを単純SELECTした時に"LIMIT 1"を押し込むようなやつを作って（まともに読み込まれたときは、messageはNULLのままで見た目変化がないっぽい）

mysql57> SELECT * FROM t1;
+------+
| num  |
+------+
|    1 |
+------+
1 row in set, 1 warning (0.00 sec)

mysql57> SHOW WARNINGS;
+-------+------+---------------------------------------------------------------------------------------+
| Level | Code | Message                                                                               |
+-------+------+---------------------------------------------------------------------------------------+
| Note  | 1105 | Query 'SELECT * FROM t1' rewritten to 'SELECT * FROM t1 LIMIT 1' by plugin: Rewriter. |
+-------+------+---------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

おお、書き換えてくれたぽい。 クエリーキャッシュぽく、クエリーの文字列で判定しているだけぽいけど

mysql57> select * FROM t1;
+------+
| num  |
+------+
|    1 |
+------+
1 row in set, 1 warning (0.00 sec)

mysql57> SELECT /* dummy */  * FROM t1;
+------+
| num  |
+------+
|    1 |
+------+
1 row in set, 1 warning (0.00 sec)

mysql57> SELECT *
    -> FROM t1;
+------+
| num  |
+------+
|    1 |
+------+
1 row in set, 1 warning (0.00 sec)

mysql57> SELECT sql_cache * FROM t1;
+------+
| num  |
+------+
|    1 |
|    2 |
|    3 |
|    4 |
|    5 |
+------+
5 rows in set (0.00 sec)

大文字小文字の吸収と、コメント, スペースや改行文字くらいは無視してくれるっぽい。SQL構文として有効なsql_cacheとか入るとさすがにダメ。簡単なプレースホルダー(?文字)は使えるけど、テーブル名の書き換えとかはできない。

SELECT以外の何かをゴニョゴニョしたかったり、テーブル名の書き換えをやりたかったら、Rewrite Pluginを自作することになるっぽい。
Write Yourself a Query Rewrite Plugin: Part 1 | MySQL Server Blog

取り敢えずrewrite_example(クエリーを全て小文字に書き換える)というのが付属しているので、

mysql57> INSTALL PLUGIN rewrite_example SONAME 'rewrite_example.so';
Query OK, 0 rows affected (0.01 sec)

mysql57> use d1
Database changed, 1 warning

mysql57> INSERT INTO t1 VALUES (100);
Query OK, 1 row affected, 1 warning (0.01 sec)

mysql57> SHOW WARNINGS;
+-------+------+------------------------------------------------------------------------------------------------------------+
| Level | Code | Message                                                                                                    |
+-------+------+------------------------------------------------------------------------------------------------------------+
| Note  | 1105 | Query 'INSERT INTO t1 VALUES (100)' rewritten to 'insert into t1 values (100)' by plugin: rewrite_example. |
| Note  | 1105 | Query 'SHOW WARNINGS' rewritten to 'show warnings' by plugin: rewrite_example.                             |
+-------+------+------------------------------------------------------------------------------------------------------------+
2 rows in set, 1 warning (0.00 sec)

うむ、INSERTもSHOWも軒並み全部イケる。こっちはC++で文字列を書き換えてるだけだから結構融通が利く感じ。

Enjoy :)