oracle open_cursors的含义及ORA-01000: 超出打开游标的最大数模拟

Property	Description
Parameter type	Integer
Default value	50
Modifiable	ALTER SYSTEM
Range of values	0 to 65535
Basic	Yes

OPEN_CURSORS

 specifies
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 of 

OPEN_CURSORS

 high 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 by 

OPEN_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, userID, 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();
}
}
}
}

或者改为如下方式：

package com.comtop;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
public class TestCursor {
public static void main(String args[]) throws Exception{
Connection con = null;
PreparedStatement pre = null;
ResultSet result = null;
try{
Class.forName("oracle.jdbc.driver.OracleDriver");
String url = "jdbc:oracle:thin:@127.0.0.1:1521:ora11";
String user = "test";
String password = "test";
con = DriverManager.getConnection(url, user, password);
for(int i=0; i<3000; i++){
String sql="select * from test where name="+i;
pre = con.prepareStatement(sql);
}
}catch (Exception e){
e.printStackTrace();
}
finally{
try{
if (result != null)
result.close();
if (pre != null)
pre.close();
if (con != null)
con.close();
}
catch (Exception e){
e.printStackTrace();
}
}
}
}