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 ofOPEN_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 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(); } } } }
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(); } } } }