Buffer Cache Size

High CPU_COUNT and increased granule size can cause ORA-0431 error.

------CPU_COUNT specifies the number of CPUs available to Oracle. On single-CPU computers, the value of CPU_COUNT is 1.

Memory sizing depends on CPU_COUNT (No of processor groups).

Please use below formulas to calculate min buffer cache size

--Minimum Buffer Cache Size

10g : max(CPU_COUNT) * max(Granule size)

11g : max(4MB * CPU_COUNT)

Please note that If SGA_MAX_SIZE < 1GB then use Granule size = 4mb, SGA_MAX_SIZE > 1G then use Granule size = 8MB.

-- _PARALLEL_MIN_MESSAGE_POOL Size

If PARALLEL_AUTOMATIC_TUNING =TRUE then large pool is used for this area otherwise shared pool is used.

CPU_COUNT*PARALLEL_MAX_SERVERS*1.5*(OS msg bufferr size) OR CPU_COUNT*5*1.5*(OS message size)

-- Add extra 2MB per CPU_COUNT for shared pool.

Here is the example:-

Sun Solaris server has threaded CPUs. 2 physical CPUs has 8 cores, and each core has 8 threads, then Oracle evaluates CPU_COUNT = 2*8*8=128.

When SGA_MAX_SIZE=900MB,

Minimum Buffer Cache = CPU_COUNT *Granule size = 128*4M = 512MB

Shared Pool can use 338MB

When SGA_MAX_SIZE=1200MB,

Minimum Buffer Cache = CPU_COUNT *Granule size = 128*8M = 1024MB

Shared Pool can use 176 MB, so ORA-4031 occurs despite larger SGA_MAX_SIZE.

You need to manually tune CPU_COUNT parameter to resolve this error.