Welcome to Part 3 of our Oracle Top Oracle Performance Tuning Interview Questions blog series! If you haven’t already, make sure to check out Part 1 and Part 2 for a comprehensive coverage of Oracle performance tuning concepts. Part 1 covers foundational concepts and beginner-level questions, while Part 2 delves into intermediate-level topics.
Oracle Performance Tuning Interview Questions Part -3
Q101. What is the “enq: TM – contention” wait event in Oracle?
A. The “enq: TM – contention” wait event occurs when a session is waiting to acquire a lock on a table due to contention with other sessions accessing the same table.
Q102. How can you investigate and resolve the “enq: TM – contention” wait event?
A. Investigating and resolving the “enq: TM – contention” wait event involves identifying the specific table causing contention, optimizing SQL statements accessing the table, adjusting transaction isolation levels, implementing appropriate locking strategies, and considering partitioning and indexing techniques.
Q103. What is the “library cache pin” wait event in Oracle?
A. The “library cache pin” wait event occurs when a session is waiting to acquire a pin on a library cache object, such as a parsed SQL statement or PL/SQL code, to ensure its stability during execution.
Q104.How can you investigate and resolve the “library cache pin” wait event?
A. Investigating and resolving the “library cache pin” wait event involves identifying the specific library cache object causing contention, optimizing SQL statement parsing and execution plans, adjusting shared pool sizing and memory management, and implementing appropriate cursor sharing mechanisms.
Q105.What is Oracle RAC and how does it improve performance?
A. Oracle RAC is a database clustering technology that allows multiple database instances to operate on different servers, sharing a common set of database files. It improves performance by enabling workload distribution across multiple nodes, providing high availability, and leveraging parallel processing capabilities for enhanced scalability.
Q106. What are the key factors to consider for optimal performance in Oracle RAC?
A. Optimal performance in Oracle RAC depends on factors such as load balancing, efficient interconnect configuration, proper resource management, effective cache fusion, optimized parallel execution, and appropriate cluster interconnect and voting disk configurations.
Q107. How can you measure and monitor performance in Oracle RAC?
A. Performance in Oracle RAC can be measured and monitored using tools such as Oracle Enterprise Manager (OEM), Oracle Real-Time Monitoring (RTM), Automatic Workload Repository (AWR), Automatic Database Diagnostic Monitor (ADDM), and cluster-specific views like V$ views and GV$ views.
Q108.What is Global Cache Fusion in Oracle RAC and how does it impact performance?
A. Global Cache Fusion is the mechanism by which Oracle RAC nodes share and access data blocks in the global cache. It impacts performance by enabling fast data access across nodes, reducing inter-instance communication overhead, and promoting efficient data sharing for concurrent transactions.
Q109.How can you optimize workload distribution and load balancing in Oracle RAC?
A.Workload distribution and load balancing in Oracle RAC can be optimized by utilizing services and service management, configuring connection load balancing, leveraging workload management policies, implementing intelligent application design, and considering affinity and anti-affinity rules.
Q110.What is Cache Fusion in Oracle RAC and how does it enhance performance?
A. Cache Fusion in Oracle RAC is the mechanism by which data blocks are transferred across nodes in response to data access requests. It enhances performance by reducing disk I/O, minimizing data transfer latency, and enabling efficient data sharing and caching across nodes.
Q111.How can you tune interconnect and network settings in Oracle RAC for optimal performance?
A. Tuning interconnect and network settings in Oracle RAC involves optimizing network bandwidth, adjusting network adapter settings, configuring Jumbo Frames for larger data transfers, enabling network teaming or bonding, and monitoring network latency and throughput for performance optimization.
Q112.What are the best practices for managing shared resources in Oracle RAC?
A. Best practices for managing shared resources in Oracle RAC include appropriate concurrency controls, optimizing lock management, minimizing data contention, utilizing scalable sequences or unique identifiers, considering partitioning and subpartitioning strategies, and leveraging Oracle RAC-specific features like Global Enqueue Services (GES) and Global Resource Directory (GRD).
Q113. How can you optimize parallel execution in Oracle RAC for improved performance?
A. Optimizing parallel execution in Oracle RAC involves setting the parallel degree appropriately, considering parallel-aware table and index structures, tuning parallel query settings, distributing work evenly across nodes, minimizing data skew, and ensuring sufficient system resources for parallel operations.
Q114. What are the considerations for optimizing high availability and performance in Oracle RAC?
A. Considerations for optimizing high availability and performance in Oracle RAC include implementing appropriate workload management policies, ensuring balanced resource allocation, designing fault-tolerant configurations, leveraging Oracle Clusterware and Grid Infrastructure features, and regularly testing and validating failover and recovery procedures.
Q115. What is the “gc buffer busy acquire” wait event in Oracle RAC?
A. The “gc buffer busy acquire” wait event occurs when a session in Oracle RAC is waiting to acquire a global cache buffer during a data access operation. It indicates contention for the buffer in the global cache across multiple instances.
Q116.How can you investigate and resolve the “gc buffer busy acquire” wait event in Oracle RAC?
A. Investigating and resolving the “gc buffer busy acquire” wait event involves identifying the specific data blocks causing contention, optimizing data distribution and affinity settings, implementing appropriate partitioning and indexing strategies, and considering buffer cache sizing and caching policies.
Q117.What is the “gc cr block busy” wait event in Oracle RAC?
A. The “gc cr block busy” wait event occurs when a session in Oracle RAC is waiting to access a data block in a consistent-read mode, but the block is currently being accessed by another session on a different instance.
Q118.How can you investigate and resolve the “gc cr block busy” wait event in Oracle RAC?
A. Investigating and resolving the “gc cr block busy” wait event involves identifying the specific data blocks causing contention, optimizing data distribution and affinity settings, adjusting transaction isolation levels, implementing appropriate locking strategies, and considering partitioning and indexing techniques.
Q119. What is the “gc current block busy” wait event in Oracle RAC?
A. The “gc current block busy” wait event occurs when a session in Oracle RAC is waiting to access a data block in a current mode, but the block is currently being accessed by another session on a different instance.
Q120. How can you investigate and resolve the “gc current block busy” wait event in Oracle RAC?
A. Investigating and resolving the “gc current block busy” wait event involves identifying the specific data blocks causing contention, optimizing data distribution and affinity settings, adjusting transaction isolation levels, implementing appropriate locking strategies, and considering partitioning and indexing techniques.
Q121. What is the “gc cr block 2-way” wait event in Oracle RAC?
A. The “gc cr block 2-way” wait event occurs when a session in Oracle RAC is waiting to read a data block in a consistent-read mode, but the block needs to be accessed from another instance, resulting in inter-instance communication.
Q122. How can you investigate and resolve the “gc cr block 2-way” wait event in Oracle RAC?
A. Investigating and resolving the “gc cr block 2-way” wait event involves analyzing the data distribution and affinity, optimizing SQL statements, reducing inter-instance communication, adjusting parallel query settings, and considering data partitioning and indexing strategies.
Q123. What is the “gc current block 2-way” wait event in Oracle RAC?
A. The “gc current block 2-way” wait event occurs when a session in Oracle RAC is waiting to access a data block in a current mode, but the block needs to be accessed from another instance, resulting in inter-instance communication.
Q124. How can you investigate and resolve the “gc current block 2-way” wait event in Oracle RAC?
A. Investigating and resolving the “gc current block 2-way” wait event involves analyzing the data distribution and affinity, optimizing SQL statements, reducing inter-instance communication, adjusting parallel query settings, and considering data partitioning and indexing strategies.
Q125.What steps would you take if a user reports a performance problem in the database or complains about a slow-running report?
A. When faced with a performance problem in the database or a slow-running report, the following practical approach can help identify and address the issue:
Gather Information:Begin by gathering specific details about the reported problem. Ask the user for information such as the exact SQL query or report name, the duration of the slowdown, and any recent changes or updates to the database or application.
Analyze Execution Plan:Examine the execution plan of the SQL query or report to understand how the database is processing the request. Identify any potential inefficiencies, such as full table scans, missing or stale indexes, or excessive I/O operations.
Check Database Statistics:Review the relevant database statistics, including system load, CPU usage, memory utilization, and I/O performance. Look for any abnormalities or resource bottlenecks that could impact overall database performance.
Identify Resource Contention:Monitor and analyze database wait events to identify any resource contention issues. Look for high wait times on critical events such as I/O waits, latch waits, or enqueue waits, which could indicate areas of contention or locking problems.
Evaluate System Configuration:Verify the system configuration settings, including database parameters, memory allocation, parallelism settings, and disk I/O configurations. Ensure they are appropriately tuned for the workload and hardware capabilities.
Review Query Optimization:Optimize the SQL query or report by examining the query execution plan, indexes, and table statistics. Consider rewriting the query, adding or modifying indexes, or utilizing query tuning techniques like bind variables or SQL plan baselines.
Check Hardware and Network:Assess the hardware infrastructure and network connectivity. Look for any hardware issues, network congestion, or latency problems that could impact database performance. Collaborate with system administrators or network specialists to resolve any identified issues.
Consider Application Design:Evaluate the application design to identify any design flaws or inefficient data retrieval methods. Analyze the report generation process and assess if any optimizations can be made, such as reducing data volume, implementing caching mechanisms, or improving query filters.
Implement Performance Monitoring:Set up ongoing performance monitoring and alerting mechanisms to proactively identify performance issues. Utilize database monitoring tools, such as Oracle Enterprise Manager (OEM) or third-party solutions, to track key performance metrics and detect anomalies.
Test and Validate Solutions:Once potential solutions are implemented, conduct thorough testing and validation to ensure the reported performance problem is resolved. Monitor the system after the changes are applied to confirm the expected performance improvements.
Q126: What is bind peeking in Oracle?
A. Bind peeking in Oracle refers to a performance optimization feature that occurs during the parsing phase of SQL statements. It involves the database optimizer examining the values of bind variables used in a SQL statement the first time it is executed and creating an execution plan based on those specific values.When a SQL statement with bind variables is parsed for the first time, Oracle’s optimizer uses a default value (typically null) to generate an execution plan. However, if subsequent executions of the same statement have different bind variable values, bind peeking comes into play.During bind peeking, the optimizer evaluates the actual values of the bind variables and considers them when generating the execution plan. This enables the optimizer to choose a more suitable plan based on the specific data characteristics, potentially leading to improved performance.Bind peeking can be beneficial when there is significant variability in the data distribution or when different bind variable values result in different execution plan efficiencies. It allows the optimizer to adapt to changing conditions and optimize the execution plan accordingly.However, it’s important to note that bind peeking may not always produce the best execution plan. If the initial execution has atypical values for the bind variables, subsequent executions with different values may suffer from suboptimal plans. This can result in performance degradation or inconsistent performance across different executions of the same statement.
Q127. What is Adaptive Cursor Sharing in Oracle?
A. Adaptive Cursor Sharing is a feature in Oracle that allows the optimizer to automatically generate and select different execution plans for a SQL statement based on the different bind variable values seen during execution. It enables the database to adapt to varying conditions and optimize query performance for different input values.
Q128. How does Adaptive Cursor Sharing work in Oracle?
A. Adaptive Cursor Sharing works by initially using a default execution plan for a SQL statement. As the statement is executed multiple times with different bind variable values, the optimizer collects statistics about the data distribution and performance. It then evaluates the different bind variable values and automatically generates and selects alternative execution plans based on the observed values.
Q129. What are the different modes of Adaptive Cursor Sharing in Oracle?
A. Oracle supports three modes of Adaptive Cursor Sharing:
Bind-Aware Mode: The optimizer automatically generates multiple execution plans based on different bind variable values.
Bind-Sensitive Mode: The optimizer uses a single execution plan that considers only the first set of bind variable values seen during execution.
Bind-Aware, but Conservative Mode: The optimizer generates multiple execution plans, but only switches execution plans if the performance improvement is significant.
Q130. How can you enable Adaptive Cursor Sharing for a SQL statement?
A. Adaptive Cursor Sharing is enabled by default in Oracle. However, you can influence its behavior by using the BIND_AWARE initialization parameter or the BIND_SENSE parameter of the BIND_AWARE cursor hint.
Q131. What are the advantages of Adaptive Cursor Sharing?
A. Adaptive Cursor Sharing offers several benefits, including:
Improved query performance for SQL statements with varying bind variable values.
Reduction in the number of hard parses and shared SQL areas.Adaptive optimization without the need for manual intervention or creating separate SQL statements for different bind variable values.
Q132. What factors can impact the effectiveness of Adaptive Cursor Sharing?
A. Several factors can impact the effectiveness of Adaptive Cursor Sharing, such as:
Data distribution: If the data distribution is skewed or the bind variable values have different selectivity, it can affect the generation of alternative execution plans.
Statistics accuracy: Accurate and up-to-date statistics are crucial for the optimizer to make informed decisions about execution plans.
Query complexity: Highly complex queries with multiple joins and subqueries may not benefit as much from Adaptive Cursor Sharing.
Q133. How can you diagnose and troubleshoot issues related to Adaptive Cursor Sharing?
A. To diagnose and troubleshoot issues with Adaptive Cursor Sharing, you can:
Analyze execution plans: Examine the execution plans generated for different bind variable values and identify any significant differences.
Collect SQL performance data: Use tools like SQL Trace or Oracle Enterprise Manager to collect detailed performance data and analyze it for any anomalies.
Adjust optimizer settings: Fine-tuning optimizer parameters like optimizer_adaptive_features and optimizer_features_enable may impact the behavior of Adaptive Cursor Sharing.
Q134.. Can you force a specific execution plan for a SQL statement with Adaptive Cursor Sharing enabled?
A. Yes, you can force a specific execution plan for a SQL statement by using hints, SQL plan baselines, or SQL profiles. However, forcing a plan can override the adaptive behavior and prevent the optimizer from generating alternative plans based on bind variable values.
Q135. Are there any limitations or considerations when using Adaptive Cursor Sharing?
A. Some considerations when using Adaptive Cursor Sharing include:
Increased parsing time for SQL statements with a high number of bind variables.The potential for suboptimal plans if the observed bind variable values do not adequately represent the overall data distribution.The need for accurate statistics and regular monitoring to ensure Adaptive Cursor Sharing is effective.
Q136. Can Adaptive Cursor Sharing be used in combination with other query optimization techniques?
A. Yes, Adaptive Cursor Sharing can be combined with other query optimization techniques such as SQL plan baselines, SQL profiles, or stored outlines. These techniques can complement each other and provide additional control over query optimization and performance.
Conclusion:
In this blog series, we have covered the top Oracle performance tuning interview questions across three parts: beginner, intermediate, and advanced levels. Whether you’re a beginner seeking foundational knowledge, an intermediate professional looking to expand your skills, or an experienced expert aiming to tackle advanced performance challenges, these questions have provided you with a comprehensive understanding of Oracle performance tuning.
From Part 1 ,where we covered essential concepts and foundational questions, to Part 2, where we delved into intermediate-level topics, and finally to Part 3, where we explored advanced-level discussions, we have equipped you with the knowledge and insights necessary to excel in Oracle performance tuning interviews.
We hope that this blog series has provided you with valuable insights, enhanced your knowledge of Oracle performance tuning, and prepared you for success in your Oracle performance tuning interviews. Remember to practice and apply these concepts in real-world scenarios to further strengthen your skills.
Continue to explore additional resources, stay updated with the latest Oracle features and advancements, and keep refining your performance tuning expertise. The world of Oracle databases is constantly evolving, and staying ahead will help you excel in your performance tuning career.
Thank you for joining us in this journey of Oracle performance tuning interview questions. We wish you the best of luck in your future endeavors!