Oracle memory optimization is one of the biggest performance levers for database systems. If memory is tuned properly, you reduce disk I/O, improve query speed, and stabilize overall system performance—especially for OLTP and large enterprise workloads.
Oracle memory tuning is mainly about balancing SGA (System Global Area) and PGA (Program Global Area) while aligning with the OS (Linux/AIX) memory behavior.
1. Oracle memory architecture (foundation)
Oracle memory is split into two main areas:
🔹 SGA (System Global Area)
Shared memory used by all sessions:
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Buffer Cache (data blocks)
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Shared Pool (SQL, PL/SQL)
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Redo Log Buffer
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Large Pool / Java Pool (optional)
👉 Purpose: Reduce disk reads and speed up SQL execution
🔹 PGA (Program Global Area)
Private memory per session:
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Sort area
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Hash joins
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Cursor operations
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Session-specific memory
👉 Purpose: Improve query processing efficiency
2. Core memory optimization strategy
✔ Balance SGA vs PGA
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OLTP → higher SGA focus
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Analytics → higher PGA focus
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Mixed workloads → balanced tuning
👉 Incorrect balance = swapping + slow queries
3. SGA optimization techniques
🔹 1. Automatic Shared Memory Management (ASMM)
Oracle automatically manages:
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Buffer cache
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Shared pool
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Large pool
👉 Best for most production systems
🔹 2. Automatic Memory Management (AMM)
Manages both SGA + PGA together.
✔ Simple to use
❌ Not ideal for large enterprise systems
🔹 3. HugePages (critical optimization)
HugePages improves SGA performance by:
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Reducing TLB misses
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Preventing memory fragmentation
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Stabilizing large SGAs
👉 Best practice:
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Disable Transparent HugePages (THP)
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Enable static HugePages allocation
🔹 4. Buffer Cache tuning
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Increase buffer cache for read-heavy workloads
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Monitor cache hit ratio
👉 Goal: reduce physical disk reads
🔹 5. Shared Pool tuning
Controls:
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SQL parsing
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PL/SQL execution
Best practices:
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Avoid excessive hard parsing
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Use bind variables
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Increase shared pool if parse contention exists
4. PGA optimization techniques
🔹 1. PGA target sizing
Controls memory for:
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Sort operations
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Hash joins
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Aggregations
👉 If too small → temp tablespace usage increases
🔹 2. Workarea tuning
Key parameter:
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workarea_size_policy = AUTO
👉 Oracle dynamically manages memory for operations
🔹 3. Reduce excessive sorting
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Add indexes
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Optimize execution plans
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Avoid unnecessary full table scans
5. OS-level memory optimization
On Linux systems
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Set proper kernel shared memory limits
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Configure HugePages correctly
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Disable swap pressure on Oracle memory
👉 Swap usage = major performance degradation
On AIX systems
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Use
vmo tuning
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Prevent paging of SGA
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Align memory with pinned memory settings
6. Memory-related performance bottlenecks
🔴 1. Insufficient SGA
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Increased disk reads
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Slow query execution
🔴 2. Insufficient PGA
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Heavy temp tablespace usage
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Slow sorting and joins
🔴 3. Memory swapping
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Severe performance drop
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System instability
🔴 4. Shared pool contention
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Hard parsing overhead
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CPU spikes
7. Advanced optimization techniques
🔹 1. Memory advisor tools
Use Oracle advisors:
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SGA Advisor
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PGA Advisor
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Memory Target Advisor
🔹 2. AWR analysis
Look for:
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Buffer cache misses
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PGA overflows
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Shared pool reloads
🔹 3. SQL tuning impact
Memory optimization is often wasted if SQL is bad.
Fix:
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Missing indexes
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Poor execution plans
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High memory-consuming joins
🔹 4. Parallel execution tuning
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Controls memory usage per session
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Prevents PGA explosion
8. Enterprise memory tuning strategy (step-by-step)
✔ Step 1: Capture baseline
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AWR reports (peak workload)
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Memory usage statistics
✔ Step 2: OS tuning
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Enable HugePages
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Disable THP
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Prevent swapping
✔ Step 3: SGA tuning
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Optimize buffer cache
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Tune shared pool
✔ Step 4: PGA tuning
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Set proper PGA target
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Reduce memory-heavy SQL operations
✔ Step 5: SQL optimization
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Fix top resource-consuming queries
✔ Step 6: Continuous monitoring
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AWR trend analysis
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Memory advisor reports
9. Best practices summary
✔ Use HugePages for SGA
✔ Disable Transparent HugePages (Linux)
✔ Avoid swapping at all costs
✔ Use ASMM for most environments
✔ Tune PGA separately for heavy queries
✔ Optimize SQL before increasing memory
✔ Monitor buffer cache hit ratio
✔ Use AWR for continuous tuning
Final takeaway
Oracle memory optimization is not just about increasing RAM—it is about efficiently allocating SGA and PGA, eliminating I/O dependency, and aligning OS memory behavior with Oracle internals.