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Wednesday, June 14, 2017

SGA_MAX_SIZE & SGA_TARGET / MEMORY_TARGET & MEMORY_MAX_TARGET

SGA_MAX_SIZE sets the overall amount of memory the SGA can consume but is not dynamic.
The SGA_MAX_SIZE parameter is the max allowable size to resize the SGA Memory area parameters.

If the SGA_TARGET is set to some value then the Automatic Shared Memory Management (ASMM) is enabled, the SGA_TARGET value can be adjusted up to the SGA_MAX_SIZE parameter, not more than SGA_MAX_SIZE parameter value.This parameter is dynamic and can be increased up to the value of SGA_MAX_SIZE
MEMORY_TARGET & MEMORY_MAX_TARGET

SGA and PGA can manage together rather than managing them separately.

If SGA_TARGET, SGA_MAX_SIZE and PGA_AGGREGATE_TARGET is set to 0 and set MEMORY_TARGET (and optionally MEMORY_MAX_TARGET) to non zero value, Oracle will manage both SGA components and PGA together within the limit specified.

If MEMORY_TARGET is set to 1024MB, Oracle will manage SGA and PGA components within itself.

If MEMORY_TARGET is set to non zero value:

SGA_TARGET, SGA_MAX_SIZE and PGA_AGGREGATE_TARGET are set to 0, 60% of memory mentioned in MEMORY_TARGET is allocated to SGA and rest 40% is kept for PGA.
SGA_TARGET and PGA_AGGREGATE_TARGET are set to non-zero values, these values will be considered minimum values.(But sum of SGA_TARGET and PGA_AGGREGATE_TARGET should be less than or equal to MEMORY_TARGET).
SGA_TARGET is set to non zero value and PGA_AGGREGATE_TARGET is not set. Still these values will be autotuned and PGA_AGGREGATE_TARGET will be initialized with value of (MEMORY_TARGET-SGA_TARGET).
PGA_AGGREGATE_TARGET is set and SGA_TARGET is not set. Still both parameters will be autotunes. SGA_TARGET will be initialized to a value of (MEMORY_TARGET-PGA_AGGREGATE_TARGET).

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