An Oracle Database instance is configured with MEMORY_TARGET set to 4 GB and MEMORY_MAX_TARGET set to 4 GB. The database administrator explicitly sets the initialization parameter SGA_TARGET to 2 GB. How does the Automatic Memory Management (AMM) mechanism treat the SGA_TARGET value in this configuration?

When Automatic Memory Management (AMM) is enabled by setting MEMORYTARGET to a non-zero value, any explicitly set value for SGATARGET is interpreted as the minimum size for the System Global Area (SGA). The AMM mechanism will dynamically resize the SGA and PGA within the total MEMORYTARGET limit to meet workload demands. However, it will not shrink the SGA to a size smaller than the value specified by SGATARGET. This allows administrators to guarantee a minimum amount of memory is always allocated to the SGA components.

B. Auto-tuning for the SGA is not disabled; SGATARGET simply sets a lower bound for the tuning, not a fixed size.
C. The SGATARGET setting is not ignored; it is actively used by AMM as a boundary condition for its resizing algorithms.
D. SGATARGET acts as a minimum, not a maximum, in this configuration. SGAMAXSIZE would serve as a hard upper limit.

1. Oracle Database Concepts, 19c, Chapter 15, "Memory Architecture", Section "About Automatic Memory Management". It states: "The SGATARGET and PGAAGGREGATETARGET parameters act as minimum size settings for their respective memory areas."

2. Oracle Database Reference, 19c, Initialization Parameters, MEMORYTARGET. The documentation explains: "If you set MEMORYTARGET, you can also set SGATARGET... SGATARGET will be treated as the minimum size of the SGA."

3. Oracle Database Performance Tuning Guide, 19c, Chapter 7, "Configuring and Using Memory", Section "Using Automatic Memory Management". It confirms that with AMM, SGATARGET specifies the minimum size of the SGA.