玩Oracle的都比较关注shared pool，特别是library cache，在使用了绑定变量（预编译sql）之后确实能得到很大的性能提升。现在在转Mysql之后特别是innodb很多东西都还能和Oracle对得上号的，就像innodb_buffer_pool_size类似于Oracle的database buffer cache，innodb_log_buffer_size类似于redo log buffer，但是innodb_additional_mem_pool_size仅仅类似于shared pool的Data dictionary cache，似乎还缺少和library cache相对应的东西。那就有一个问题了，在Mysql里面使用预编译的sql还会有性能提升吗？
这里我用Java的jdbc做了一下测试，分别用Statement和PreparedStatement执行1000个sql，并运行10次
1.使用Statement做硬解析：
1 package exmysql; 2 3 import java.sql.Connection; 4 import java.sql.DriverManager; 5 import java.sql.ResultSet; 6 import java.sql.SQLException; 7 import java.sql.Statement; 8 import java.util.Date; 9 10 public class adddata {11 12 private static long worker(){13 Date begin = new Date(); 14 15 String driver="com.mysql.jdbc.Driver";16 17 String url="jdbc:mysql://172.16.2.7:3306/testdb";18 19 Connection conn=null;20 Statement stmt=null;21 ResultSet rs=null;22 23 try{24 Class.forName(driver);25 conn=DriverManager.getConnection(url,"dbaadmin","123456");26 stmt=conn.createStatement();27 String sql;28 for (int i=1;i<=5000;i++){29 sql="select * from test1 where id="+i;30 rs=stmt.executeQuery(sql);31 }32 }33 catch(SQLException | ClassNotFoundException e){34 e.printStackTrace();35 }36 37 if(stmt!=null){38 try{39 stmt.close();40 }41 catch(SQLException e){42 e.printStackTrace();43 }44 }45 46 if(conn!=null){47 try{48 conn.close();49 }50 catch(SQLException e){51 e.printStackTrace();52 }53 }54 55 Date end = new Date(); 56 return end.getTime()-begin.getTime();57 }58 59 public static void main(String[] args) {60 // TODO Auto-generated method stub61 62 long elapsed,average;63 average=0;64 for (int i=1;i<=10;i++){65 elapsed=worker();66 System.out.println("elapsed time(ms):"+elapsed);67 average=average+elapsed;68 }69 System.out.println("average time(ms):"+average/10);70 }71 72 }
结果如下：
elapsed time(ms):24652
elapsed time(ms):13380
elapsed time(ms):13250
elapsed time(ms):13877
elapsed time(ms):13275
elapsed time(ms):13193
elapsed time(ms):19022
elapsed time(ms):13558
elapsed time(ms):14138
elapsed time(ms):13364
average time(ms):15170
2.同样的sql用PreparedStatement预编译执行
1 package exmysql; 2 3 import java.sql.*; 4 import java.util.Date; 5 6 public class insert_data { 7 8 private static long worker(){ 9 Date begin = new Date(); 10 11 String driver="com.mysql.jdbc.Driver";12 13 String url="jdbc:mysql://172.16.2.7:3306/testdb";14 15 Connection conn=null;16 PreparedStatement pstm=null;17 ResultSet rs=null;18 19 try{20 Class.forName(driver);21 conn=DriverManager.getConnection(url,"dbaadmin","123456");22 String sql="select * from test1 where id=?";24 pstm=conn.prepareStatement(sql);25 for(int i=1;i<=5000;i++){26 pstm.setInt(1, i);27 rs=pstm.executeQuery();28 }29 31 }32 catch(SQLException | ClassNotFoundException e){33 e.printStackTrace();34 }35 36 if(pstm!=null){37 try{38 pstm.close();39 }40 catch(SQLException e){41 e.printStackTrace();42 }43 }44 45 if(conn!=null){46 try{47 conn.close();48 }49 catch(SQLException e){50 e.printStackTrace();51 }52 }53 54 Date end = new Date(); 55 return end.getTime()-begin.getTime();56 }57 58 public static void main(String[] args) {59 // TODO Auto-generated method stub60 61 long elapsed,average;62 average=0;63 for (int i=1;i<=10;i++){64 elapsed=worker();65 System.out.println("elapsed time(ms):"+elapsed);66 average=average+elapsed;67 }68 System.out.println("average time(ms):"+average/10);69 }70 71 }
结果如下：
elapsed time(ms):14773
elapsed time(ms):16352
elapsed time(ms):14797
elapsed time(ms):15800
elapsed time(ms):12069
elapsed time(ms):14953
elapsed time(ms):13238
elapsed time(ms):12366
elapsed time(ms):15263
elapsed time(ms):13089
average time(ms):14270
可以看出两种方式执行的结果几乎相同，不像Oracle差距那么大。而且就算是用PreparedStatement的方式，在Mysql数据库端抓出来的sql语句也不是以变量id=?的形式出现的，而是实际的数值。后来在网上看到在连接字符串上加上useServerPrepStmts=true可以实现真正的预编译
String url="jdbc:mysql://172.16.2.7:3306/testdb"; url=url+"?useServerPrepStmts=true";
加上这段后可以在数据库端可以看到明确的结果：
mysql> show global status like 'Com_stmt_prepare';
+------------------+-------+
| Variable_name | Value |
+------------------+-------+
| Com_stmt_prepare | 11 |
+------------------+-------+
1 row in set (0.00 sec)
但是实际的运行结果和上面几乎一样，性能上也没有任何的提升。由此可以推断出Mysql由于缺少类似于Oracle的library cache的部件，因此采用预编译方式执行sql是没有性能上的提升的。