Why Does 'java.sql.SQLException: - ORA-01000: maximum open cursors exceeded' Occur in Java?

Why "java.sql.SQLException: - ORA-01000: maximum open cursors exceeded" Error Occurs

The ORA-01000 exception arises when an application attempts to open more result sets in Java than the maximum number of cursors configured on the database. This can happen due to configuration mistakes or cursor leaks.

1. Maximum Open Cursors and JDBC Connections

Maximum open cursors are unrelated to the number of JDBC connections. They specifically limit the number of result sets (cursors) a single connection can simultaneously hold.

2. Configuring Statement/ResultSet Objects

The number of statement or resultset objects in a database cannot be explicitly configured like connections. However, these objects are tied to cursors on the database.

3. Instance vs. Method Local Statement/ResultSet Objects

In a single-threaded environment, holding statement and resultset objects as instance variables is advisable to avoid frequent creation and closure. This approach improves performance but should be used carefully in multi-threaded contexts.

4. Looping with Prepared Statements

Executing a prepared statement in a loop can indeed cause this issue if the statement is not closed after each iteration. Each execution creates a new result set that consumes a cursor. Closing the statement after the loop releases all cursors associated with its result sets.

5. Multiple Statement/PreparedStatement Creations

Calling conn.createStatement() and conn.prepareStatement(sql) multiple times on a single connection creates new statement objects. Each statement can execute queries and create result sets, which use up cursors on the database.

6. Weak/Soft Reference Statement Objects for Leak Prevention

Weak or soft references are not useful for preventing cursor leaks. These references allow objects to be garbage collected earlier than expected, which may lead to situations where result sets are closed prematurely, resulting in unexpected errors.

7. Tracking Open Cursor Information in Oracle Database

To identify open cursors in an Oracle database:

• Log in to the database as a DBA (sqlplus / as sysdba).
• Run the following query:

SELECT   A.VALUE,
        S.USERNAME,
        S.SID,
        S.SERIAL#
FROM V$SESSTAT A,
     V$STATNAME B,
     V$SESSION S
WHERE A.STATISTIC# = B.STATISTIC#
  AND S.SID        = A.SID
  AND B.NAME       = 'opened cursors current'
  AND USERNAME     = 'USERNAME';

where USERNAME should be replaced with the user's name.

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