OPEN_CURSORSspecifies the maximum number of open cursors (handles to private SQL areas) a session can have at once. You can use this parameter to prevent a session from opening an excessive number of cursors.

It is important to set the value ofOPEN_CURSORShigh enough to prevent your application from running out of open cursors. The number will vary from one application to another. Assuming that a session does not open the number of cursors specified byOPEN_CURSORS,there is no added overhead to setting this value higher than actually needed.

OPEN_CURSORS是一个session一次最多打开的游标数量，就是执行SQL的数量，一般有问题是程序写的有问题。

SQL> select * from v$version;
BANNER
—————————————————————————
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 – 64bit Production
PL/SQL Release 11.2.0.3.0 – Production
CORE 11.2.0.3.0Production
TNS for Linux: Version 11.2.0.3.0 – Production
NLSRTL Version 11.2.0.3.0 – Production

SQL> show parameter open_cursor
NAME TYPE VALUE
———————————— ———– ————-
open_cursors integer 300

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class TestOpenCursor {
    static final String driver_class  = "oracle.jdbc.driver.OracleDriver";
    static final String connectionURL = "jdbc:oracle:thin:@10.10.151.15:1521:orcl";
    static final String userID        = "TEST";
    static final String userPassword  = "TEST";
    public static void main(String[] args) {
            Connection  con = null;
            Statement   stmt = null;
            ResultSet   rset = null;
            String  query_string = "SELECT * FROM test where rownum=1";
            try {
                Class.forName (driver_class).newInstance();
                con = DriverManager.getConnection(connectionURL,userID,userPassword);
                for(int i=0; i<=300; i++){
                    stmt = con.createStatement();
                    rset = stmt.executeQuery (query_string);
                    while (rset.next ()) {
                         rset.getString(1);
                    }
                }
                rset.close();
                stmt.close();
            }  catch (SQLException e) {
                e.printStackTrace();
            } catch (Exception e) {
                e.printStackTrace();
            }
    }
}

java.sql.SQLException: ORA-01000: 超出打开游标的最大数
at oracle.jdbc.driver.T4CTTIoer.processError(T4CTTIoer.java:445)
at oracle.jdbc.driver.T4CTTIoer.processError(T4CTTIoer.java:396)
at oracle.jdbc.driver.T4C8Oall.processError(T4C8Oall.java:879)
at oracle.jdbc.driver.T4CTTIfun.receive(T4CTTIfun.java:450)
at oracle.jdbc.driver.T4CTTIfun.doRPC(T4CTTIfun.java:192)
at oracle.jdbc.driver.T4C8Oall.doOALL(T4C8Oall.java:531)
at oracle.jdbc.driver.T4CStatement.doOall8(T4CStatement.java:193)
at oracle.jdbc.driver.T4CStatement.executeForDescribe(T4CStatement.java:873)
at oracle.jdbc.driver.OracleStatement.executeMaybeDescribe(OracleStatement.java:1167)
at oracle.jdbc.driver.OracleStatement.doExecuteWithTimeout(OracleStatement.java:1289)
at oracle.jdbc.driver.OracleStatement.executeQuery(OracleStatement.java:1491)
at oracle.jdbc.driver.OracleStatementWrapper.executeQuery(OracleStatementWrapper.java:406)
at TestOpenCursor.main(TestOpenCursor.java:22)
上面的代码有两个问题：1.循环创建了Statement，而关闭在循环外。如果关闭也放在循环内，可以避免ORA-01000的错误，但效率不高，每次打开与关闭消耗太多的时间。 2.最后要写finally,保证绝对的关闭。

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class TestOpenCursor {
    static final String driver_class  = "oracle.jdbc.driver.OracleDriver";
    static final String connectionURL = "jdbc:oracle:thin:@10.10.151.15:1521:orcl";
    static final String userID        = "TEST";
    static final String userPassword  = "TEST";
    public static void main(String[] args) {
            Connection  con = null;
            Statement   stmt = null;
            ResultSet   rset = null;
            String  query_string = "SELECT * FROM test where rownum=1";
            try {
                Class.forName (driver_class).newInstance();
                con = DriverManager.getConnection(connectionURL,userPassword);
                stmt = con.createStatement();
                for(int i=0; i<=300; i++){
                    rset = stmt.executeQuery (query_string);
                    while (rset.next ()) {
                         rset.getString(1);
                    }
                }
                rset.close();
                stmt.close();
            }  catch (SQLException e) {
                e.printStackTrace();
            } catch (Exception e) {
                e.printStackTrace();
            }finally{
                try{
                    if(rset != null){
                        rset.close();
                    }
                    if(stmt != null){
                        stmt.close();
                    }
                }catch(Exception e){
                    e.printStackTrace();
                }
            }
    }
}