The Program Global Area (PGA) is a private memory region that contains the data and control information for a server process. Only a server process can access the PGA. Oracle Database reads and writes information in the PGA on behalf of the server process. An example of such information is the run-time area of a cursor. Each time a cursor is executed, a new run-time area is created for that cursor in the PGA memory region of the server process executing that cursor.

Note:
Part of the run-time area can be located in the Shared Global Area (SGA) when using shared servers.

For complex queries (such as decision support queries), a big portion of the run-time area is dedicated to work areas allocated by memory intensive operators, including:
1)	Sort-based operators, such as ORDER BY, GROUP BY, ROLLUP, and window functions
2)	Hash-join
3)	Bitmap merge
4)	Bitmap create
5)	Write buffers used by bulk load operations

A sort operator uses a work area (the sort area) to perform the in-memory sorting of a set of rows. Similarly, a hash-join operator uses a work area (the hash area) to build a hash table from its left input.

ORA-04036: PGA memory used by the instance exceeds PGA_AGGREGATE_LIMIT
Cause: Private memory across the instance exceeded the limit specified in the PGA_AGGREGATE_LIMIT initialization parameter. The largest sessions using Program Global Area (PGA) memory were interrupted to get under the limit.
Action: Increase the PGA_AGGREGATE_LIMIT initialization parameter or reduce memory usage.

PGA LIMIT: pid 317111 is ineligible for an ORA-4036 interrupt
System processes and most background processes cannot receive ORA-4036
interrupts. When they are contributing to the instance exceeding
PGA_AGGREGATE_LIMIT, they will periodically dump their PGA usage.
PGA LIMIT: pid 317124 is a top contributor to going over PGA_AGGREGATE_LIMIT
PGA LIMIT: pid 317124 is ineligible for an ORA-4036 interrupt
PGA LIMIT: pid 317120 is a top contributor to going over PGA_AGGREGATE_LIMIT
PGA LIMIT: pid 317120 is ineligible for an ORA-4036 interrupt

--在CDB中修改：
[[email protected] ~]$ sqlplus / as sysdba

SQL*Plus: Release 12.2.0.1.0 Production on Mon Apr 17 05:29:27 2017

Copyright (c) 1982, 2016, Oracle.  All rights reserved.


Connected to:
Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production

SQL> show pdbs

    CON_ID CON_NAME			  OPEN MODE  RESTRICTED
---------- ------------------------------ ---------- ----------
	 2 PDB$SEED			  READ ONLY  NO
	 3 DAVE 			  READ WRITE NO
SQL> show con_name

CON_NAME
------------------------------
CDB$ROOT
SQL> show parameter pga

NAME				     TYPE	 VALUE
------------------------------------ ----------- ------------------------------
pga_aggregate_limit		     big integer 2G
pga_aggregate_target		     big integer 0
SQL> alter system set pga_aggregate_limit=3g;

System altered.

SQL> show parameter pga

NAME				     TYPE	 VALUE
------------------------------------ ----------- ------------------------------
pga_aggregate_limit		     big integer 3G
pga_aggregate_target		     big integer 0
SQL>   

--在PDB中修改：
[[email protected] admin]$ cat tnsnames.ora 
# tnsnames.ora Network Configuration File: /u01/app/oracle/product/12.2.0/dbhome_1/network/admin/tnsnames.ora
# Generated by Oracle configuration tools.

LISTENER_CNDBA =
  (ADDRESS = (PROTOCOL = TCP)(HOST = single)(PORT = 1521))


CNDBA =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = single)(PORT = 1521))
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = cndba)
    )
  )
dave =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = single)(PORT = 1521))
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = dave)
    )
  )

[[email protected] admin]$ sqlplus [email protected]

SQL*Plus: Release 12.2.0.1.0 Production on Mon Apr 17 05:38:02 2017

Copyright (c) 1982, 2016, Oracle.  All rights reserved.


Connected to:
Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production

SQL> show con_name

CON_NAME
------------------------------
DAVE
SQL>
SQL> show parameter pga

NAME				     TYPE	 VALUE
------------------------------------ ----------- ------------------------------
pga_aggregate_limit		     big integer 3G
pga_aggregate_target		     big integer 0
SQL> alter system set pga_aggregate_limit=2g;

System altered.

SQL> show parameter pga

NAME				     TYPE	 VALUE
------------------------------------ ----------- ------------------------------
pga_aggregate_limit		     big integer 2G
pga_aggregate_target		     big integer 0
SQL>

--此时查看CDB中的参数，还是3G:
SQL>  show parameter pga

NAME				     TYPE	 VALUE
------------------------------------ ----------- ------------------------------
pga_aggregate_limit		     big integer 3G
pga_aggregate_target		     big integer 0
SQL>