Please also reference my previous post in this series:
Oracle’s OPS Insights: Database Performance Analytics for Everyone — Roger Cornejo
Introduction to SQL Insights: Cursor Invalidation Storms — Roger Cornejo
Introduction to SQL Insights: Understanding Execution Plan Changes — Roger Cornejo
Introduction to SQL Insights: Understanding the Cursor Sharing Issue
In Oracle databases, cursor sharing is essential for efficient memory usage and overall system performance. When SQL statements are executed, Oracle attempts to reuse existing cursors—precompiled SQL statements stored in the shared pool memory area—rather than creating new cursors. Cursor sharing ensures that similar SQL statements, differing only in literals or bind variables, use the same execution plan and resources. However, when cursors are not shared, the database can become overloaded with thousands of similar but distinct SQL statements, leading to excessive memory consumption, increased parsing overhead (read CPU consumption), and potential performance bottlenecks. This lack of cursor sharing is a common root cause of performance degradation in Oracle databases.
The Role of SQL Insights in Identifying the Cursor Sharing Issue
SQL Insights is equipped with algorithms specifically designed to detect cursor sharing issues. It continuously monitors SQL activity in the database, identifying patterns where similar SQL statements are not sharing cursors as expected. By analyzing key metrics such as the number of child cursors generated for similar SQL statements, SQL Insights can pinpoint areas where cursor sharing is suboptimal. This automated detection allows developers, support teams, and DBAs to gain visibility into problematic SQL behavior without the need for manual investigation.
Flagging Problematic Cursor Sharing Issues
One of the key features of SQL Insights is its ability to flag problematic cursor sharing issues in real-time. When SQL Insights detects that a high number of similar SQL statements are not sharing cursors—resulting in excessive child cursors and increased memory usage—it flags this as a potential performance concern. By alerting users to this issue early, SQL Insights enables timely intervention, such as optimizing SQL code to use bind variables or adjusting cursor sharing parameters. This proactive approach helps prevent the shared pool from becoming overwhelmed and ensures more efficient use of database resources.
Why Flagging the Cursor Sharing Issue Matters
Flagging cursor sharing issues is critical for maintaining database performance, especially in environments with high transaction and query volumes. Without proper cursor sharing, the shared pool can quickly become saturated, leading to increased hard parsing, contention for shared memory, and overall system slowdowns. By providing early warnings about these issues, SQL Insights empowers database professionals to address them before they escalate, reducing the risk of performance degradation and improving the overall efficiency of the database.
Solutions to the Cursor Sharing Issue:
The best solution to the cursor sharing issue is to use bind variables in when developing the SQL. Sometimes this is beyond the control of the DBA or support person (e.g. vendor software; dev team does not have the bandwidth; …), so they might be tempted to set the database initialization parameter “cursor_sharing = force” which is a rather blunt instrument for solving the problem. Generally, I caution against this because of the major knock-on effect of changing every literal in every SQL statement to a bind variable. This will basically cause all your SQL with literals to get new execution plans, and it is not always for the best [I’ve had cases where it destroyed performance in production systems (thankfully the change is easy to rollback 😊)]. Therefore, I only endorse the “cursor_sharing = force” solution if it is recommended and certified by the vendor or the dev/support team has a good capability of doing regression testing at production workloads [or you like to take big risks 😉].
Conclusion: Enhancing Performance Management with SQL Insights
In summary, SQL Insights plays a crucial role in enhancing Oracle database performance management by detecting and flagging cursor sharing issues. By identifying when similar SQL statements are not efficiently sharing cursors, SQL Insights helps developers, support teams, and DBAs optimize SQL execution and manage database resources more effectively. This capability ensures that the database can handle high transaction volumes without unnecessary overhead, maintaining the performance and stability needed to meet business demands.