Which is better for minimizing swap usage?
AMM (Automatic Memory Management)
- MEMORY_TARGET
ASMM (Automatic Shared Memory Management)
- SGA_TARGET
In most real-world Oracle deployments, using manual memory management (i.e., SGA_TARGET + PGA_AGGREGATE_TARGET) results in lower swap usage than MEMORY_TARGET / MEMORY_MAX_TARGET.
Why MEMORY_TARGET causes more swap usage
Automatic Memory Management (AMM), which uses:
MEMORY_TARGET
MEMORY_MAX_TARGET
requires a Linux system to allocate a large shared memory segment plus additional OS memory for management.
On Linux, AMM uses /dev/shm (tmpfs), and if its size is less than MEMORY_TARGET, Oracle falls back to regular pages, increasing swap pressure.
Problems with MEMORY_TARGET:
Tends to cause kernel swapping due to dynamic resizing of SGA/PGA.
Additional overhead for memory rebalancing.
On NUMA servers, AMM can mismatch memory locality → more swap.
Oracle itself recommends NOT using AMM on production systems.
Oracle Docs: AMM is mainly recommended for small dev/test systems, not production.
Why SGA_TARGET results in lower swap usage
SGA_TARGET uses Automatic Shared Memory Management (ASMM).
Memory is allocated in huge pages (if enabled), giving performance and eliminating swap spikes.
With:
SGA_TARGET (or even SGA_MAX_SIZE)
PGA_AGGREGATE_TARGET
Oracle uses memory more predictably:
Benefits:
Stable memory footprint → no resizing storms.
Huge Pages support → swap is effectively zero.
No tmpfs (/dev/shm) dependency.
Fits well with modern Linux kernel memory management.
Oracle recommends ASMM for production databases.
Winner for swap control: SGA_TARGET (ASMM) If your goal is:
- avoid swap
- maintain predictable memory usage
- use huge pages
- ensure performance stability
Use SGA_TARGET + PGA_AGGREGATE_TARGET (ASMM).
Recommended Production Setup:
MEMORY_TARGET=0
MEMORY_MAX_TARGET=0
SGA_TARGET=<value>
SGA_MAX_SIZE=<value>
PGA_AGGREGATE_TARGET=<value>
Enable Huge Pages on Linux for optimal performance.
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