Mybatis之开启MySQL的预编译功能 原
本文参考博客https://my.oschina.net/kailuncen/blog/905395，后自己验证的。
最重要的参数，如下List-1:
List-1
useServerPrepStmts=true&&cachePrepStmts=true首先来看不加List-1参数的情况，如下List-2:
List-2
url=jdbc:mysql://127.0.0.1:3306/mjduan?useUnicode=true&characterEncoding=utf-8&useSSL=false服务器端MySQL的general日志里面内容如下List-3:
List-3 执行的三条语句被打印出来了
2018-06-12T23:37:54.142048Z 10 Query SET NAMES utf8
2018-06-12T23:37:54.143931Z 10 Query SET character_set_results = NULL
2018-06-12T23:37:54.145705Z 10 Query SET autocommit=1
2018-06-12T23:37:54.210026Z 10 Query SELECT id,name,age FROM student WHERE id = 1
2018-06-12T23:37:54.236635Z 10 Query SELECT id,name,age FROM student WHERE id = 1
2018-06-12T23:37:54.239985Z 10 Query SELECT id,name,age FROM student WHERE id = 1JDBC连接的url中添加useServerPrepStmts=true，如下List-4:
List-4
url=jdbc:mysql://127.0.0.1:3306/mjduan?useUnicode=true&characterEncoding=utf-8&useSSL=false&&useServerPrepStmts=true下面的List-5中，每个Ececute之前都有一个Prepare，说明执行SQL之前，都对该SQL进行解析、优化了，所以没有起到预编译的作用。
List-5
2018-06-12T23:29:34.175252Z 5 Query SET NAMES utf8
2018-06-12T23:29:34.176954Z 5 Query SET character_set_results = NULL
2018-06-12T23:29:34.178768Z 5 Query SET autocommit=1
2018-06-12T23:29:34.214910Z 5 Prepare SELECT id,name,age FROM student WHERE id = ?
2018-06-12T23:29:34.244389Z 5 Execute SELECT id,name,age FROM student WHERE id = 1
2018-06-12T23:29:34.265083Z 5 Close stmt
2018-06-12T23:29:34.266680Z 5 Prepare INSERT INTO student(name,age) VALUES(?, ?)
2018-06-12T23:29:34.268304Z 5 Query select @@session.tx_read_only
2018-06-12T23:29:34.275772Z 5 Execute INSERT INTO student(name,age) VALUES('明明', 20)
2018-06-12T23:29:34.283289Z 5 Close stmt
2018-06-12T23:29:34.284142Z 5 Prepare SELECT id,name,age FROM student WHERE id = ?
2018-06-12T23:29:34.285013Z 5 Execute SELECT id,name,age FROM student WHERE id = 1
2018-06-12T23:29:34.287157Z 5 Close stmtJDBC连接的url加上useServerPrepStmts=true&cachePrepStmts=true，如下List-6所示:
List-6
url=jdbc:mysql://127.0.0.1:3306/mjduan?useUnicode=true&characterEncoding=utf-8&useSSL=false&&useServerPrepStmts=true&cachePrepStmts=true再去看MySQL的general日志，如List-7，这次生效了。
List-7 执行三条一样的语句，只有一次Prepare
2018-06-12T23:44:03.197228Z 11 Query SET NAMES utf8
2018-06-12T23:44:03.202524Z 11 Query SET character_set_results = NULL
2018-06-12T23:44:03.206439Z 11 Query SET autocommit=1
2018-06-12T23:44:03.310079Z 11 Prepare SELECT id,name,age FROM student WHERE id = ?
2018-06-12T23:44:03.378740Z 11 Execute SELECT id,name,age FROM student WHERE id = 1
2018-06-12T23:44:03.427651Z 11 Execute SELECT id,name,age FROM student WHERE id = 1
2018-06-12T23:44:03.431207Z 11 Execute SELECT id,name,age FROM student WHERE id = 1注意:
预编译功能只是在同一个Connection中生效，一个Connection无法获取另一个Connection中的预编译结果。
所以，使用Mybatis时，预编译功能只在同一个SqlSession中生效？这种说明不对，俩个SqlSession有可能拿到的是同一个Connection(因此DataSource)，这个时候这俩个SqlSession就能共享该Connection中的预编译结果。
预编译，其实有些人说预准备更恰当，不过现在几本都说预编译了。
参考：
1. https://my.oschina.net/kailuncen/blog/905395
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