Why Am I Getting ORA-01000: Maximum Open Cursors Exceeded?

Troubleshooting ORA-01000: Maximum Open Cursors Exceeded

Understanding Open Cursors

In Oracle databases, cursors are used to manage data fetch operations. Each open cursor consumes memory and system resources. The number of available cursors is limited on each instance.

Maximum Open Cursors Limit Exceeded

The ORA-01000 error occurs when the number of open cursors exceeds the maximum configured limit. This can happen due to:

• Configuration Mismatch: The number of connections or threads accessing the database exceeds the allowed cursors.
• Cursor Leaks: JDBC ResultSets are backed by database cursors, and forgetting to close these objects can lead to cursor leaks.

Resolving the Issue

1. Increase Open Cursor Count:
If possible, increase the OPEN_CURSORS setting on the database instance to accommodate the increased load.

2. Prevent Cursor Leaks:

• Properly close ResultSets using the close() method.
• Use try-with-resources blocks or AutoCloseable to ensure automatic closure.
• Avoid storing ResultSet references in instance variables.

Determining Open Cursors

To find open cursors on an Oracle instance for a specific user:

1. Connect to Oracle as SYSDBA.

2. Run the 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     = 'USER_NAME';

Logging and Monitoring

1. Runtime Logging:
Add logging statements to debug and detect cursor leaks. Monitor the number of open cursors using SQL Developer's "Monitor SQL" feature or third-party tools like TOAD.

2. Connection Pooling:
Use a connection pool to manage and reuse connections, reducing the number of open cursors.

Using Weak References

Using WeakReferences to close connections is generally not recommended. Soft or weak references can delay GC, leading to unclosed cursors and resource leaks.

Closing Cursors in Loops

Executing prepared statements in a loop does not by itself cause the ORA-01000 error. However, if the loop is not properly structured or ResultSets are not closed, it can contribute to cursor leaks.

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