SGA and PGA

The System Global Area (SGA) contains
  • Buffer Cache:
    • DB-Blocks
  • Shared Pool:
    • Library Cache (SQL-Statements)
    • Dictionary Cache
  • Large Pool
    • Message Buffers used in parallel execution of statements
    • Buffers for RMAN
  • Redo Log Buffer
  • Java Pool
  • Some other things


The Program Global Area (PGA) contains
  • Private SQL Area:
    • Bind Information
  • SQL Work Area:
    • Sort Area
    • Hash Area
    • ...


Some Queries

How big is the SGA?

SQL> show sga

Total System Global Area 8551575552 bytes
Fixed Size                  2238616 bytes
Variable Size            4211083112 bytes
Database Buffers         4328521728 bytes
Redo Buffers                9732096 bytes

If Automatic Memory Management is enabled, the following _target parameters are set:

SQL> show parameter memory

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
hi_shared_memory_address             integer     0
memory_max_target                    big integer 8G
memory_target                        big integer 7504M
shared_memory_address                integer     0

Find out the currenct size oft the memory:

SQL> COLUMN component FORMAT A30
SQL> SELECT COMPONENT, ROUND(CURRENT_SIZE/1024/1024) CURRENT_SIZE ,
  2  ROUND(MIN_SIZE/1024/1024) MIN, ROUND(MAX_SIZE/1024/1024) MAX
  3  FROM V$MEMORY_DYNAMIC_COMPONENTS;

COMPONENT                      CURRENT_SIZE        MIN        MAX
------------------------------ ------------ ---------- ----------
shared pool                            2272        704       2336
large pool                               32         32        864
java pool                                64         64         96
streams pool                             32          0         32
SGA Target                             6576       5264       6832
DEFAULT buffer cache                   4128       4096       5136
KEEP buffer cache                         0          0          0
RECYCLE buffer cache                      0          0          0
DEFAULT 2K buffer cache                   0          0          0
DEFAULT 4K buffer cache                   0          0          0
DEFAULT 8K buffer cache                   0          0          0
DEFAULT 16K buffer cache                  0          0          0
DEFAULT 32K buffer cache                  0          0          0
Shared IO Pool                            0          0          0
PGA Target                              592        336       2240
ASM Buffer Cache                          0          0          0



Empty parts of the SGA:

Alter system flush shared pool;

Alter system flush buffer cache;

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