- Briefly explain why Oracle performance tuning is critical. Briefly explain why Oracle performance tuning is critical. - Introduce the concept of hidden/underscore (“_”) parameters. Introduce the concept of hidden/underscore (“_”) parameters. - Disclaimer: hidden parameters should be changed only with Oracle Support guidance. Disclaimer: hidden parameters should be changed only with Oracle Support guidance. - Tease that the blog covers 10 highly impactful hidden parameters. Tease that the blog covers 10 highly impactful hidden parameters.

- Internal engine controls Internal engine controls - Optimizer behavior, memory, caching Optimizer behavior, memory, caching - Not visible in standard parameter lists Not visible in standard parameter lists

- Support restrictions Support restrictions - Upgrade conflicts Upgrade conflicts - Instability if misconfigured Instability if misconfigured

- Querying and Querying and - Query examples Query examples - Caution before modifying Caution before modifying

- Improves cardinality and plan stability Improves cardinality and plan stability - Helps when statistics fluctuate Helps when statistics fluctuate - When to use / when to avoid When to use / when to avoid

- Enables direct reads for full table scans Enables direct reads for full table scans - Boosts performance for large tables Boosts performance for large tables - Ideal for data warehouse environments Ideal for data warehouse environments

- Controls when table is considered “small” Controls when table is considered “small” - Impacts caching behavior Impacts caching behavior - Best use cases during OLTP bursts Best use cases during OLTP bursts

- Reduces excessive optimizer permutations Reduces excessive optimizer permutations - Useful in systems with complex joins Useful in systems with complex joins - Prevents CPU spikes during parsing Prevents CPU spikes during parsing

- Influences multiblock I/O behavior Influences multiblock I/O behavior - Helps in tuning large sequential reads Helps in tuning large sequential reads - Can improve throughput Can improve throughput

- Controls cursor aging Controls cursor aging - Boosts performance in high-soft-parse environments Boosts performance in high-soft-parse environments - Helps shared pool efficiency Helps shared pool efficiency

- Enables custom tuning category Enables custom tuning category - Useful when using SQL Tuning Advisor Useful when using SQL Tuning Advisor - Separates business workloads Separates business workloads

- Improves undo behavior Improves undo behavior - Prevents ORA-01555 in heavy workloads Prevents ORA-01555 in heavy workloads - Optimizes retention automatically Optimizes retention automatically

- Chooses between CPU-based and IO-based cost model Chooses between CPU-based and IO-based cost model - Impacts execution plans Impacts execution plans - Better performance in certain workloads Better performance in certain workloads

- Improves fetch efficiency for sequential row access Improves fetch efficiency for sequential row access - Helpful in PL/SQL loops Helpful in PL/SQL loops - Boosts response time for batch operations Boosts response time for batch operations

- Before/after results Before/after results - Statistics comparison Statistics comparison