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Thursday, December 28, 2017

Automatic Memory Management (AMM) in Oracle Database 11g R2


Identify Memory Requirement.

Following queries show you how to display the relevant memory information and how to combine with a single statement to calculate the required values.

-- Individual values.
COLUMN name FORMAT A30
COLUMN value FORMAT A10

SELECT name, value
FROM   v$parameter
WHERE  name IN ('pga_aggregate_target', 'sga_target')
UNION
SELECT 'maximum PGA allocated' AS name, TO_CHAR(value) AS value
FROM   v$pgastat
WHERE  name = 'maximum PGA allocated';

-- Calculate MEMORY_TARGET
SELECT sga.value + GREATEST(pga.value, max_pga.value) AS memory_target
FROM (SELECT TO_NUMBER(value) AS value FROM v$parameter WHERE name = 'sga_target') sga,
     (SELECT TO_NUMBER(value) AS value FROM v$parameter WHERE name = 'pga_aggregate_target') pga,
     (SELECT value FROM v$pgastat WHERE name = 'maximum PGA allocated') max_pga;

Assuming our required setting was 10G, we might issue the following statements.

CONN / AS SYSDBA
-- Set the static parameter. Leave some room for possible future growth without restart.
ALTER SYSTEM SET MEMORY_MAX_TARGET=15G SCOPE=SPFILE;

-- Set the dynamic parameters. Assuming Oracle has full control.
ALTER SYSTEM SET MEMORY_TARGET=10G SCOPE=SPFILE;
ALTER SYSTEM SET PGA_AGGREGATE_TARGET=0 SCOPE=SPFILE;
ALTER SYSTEM SET SGA_TARGET=0 SCOPE=SPFILE;
ALTER SYSTEM SET SGA_MAX_SIZE=0 SCOPE=SPFILE;


-- Restart instance.
SHUTDOWN IMMEDIATE;
STARTUP;

Once the database is restarted the MEMORY_TARGET parameter can be amended as required without an instance restart.

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