如何優化oracle pga

1* select * from v$pga_target_advice

PGA_TARGET_FOR_ESTIMATE PGA_TARGET_FACTOR ADV BYTES_PROCESSED ESTD_EXTRA_BYTES_RW ESTD_PGA_CACHE_HIT_PERCENTAGE ESTD_OVERALLOC_COUNT
----------------------- ----------------- --- --------------- ------------------- ----------------------------- --------------------
               65536000                 0 ON        269923328           103311360                            72                    0
              131072000                 0 ON        269923328           103311360                            72                    0
              262144000                 1 ON        269923328                   0                           100                    0
              393216000                 1 ON        269923328                   0                           100                    0
              524288000                 1 ON        269923328                   0                           100                    0
              629145600                 1 ON        269923328                   0                           100                    0
              734003200                 1 ON        269923328                   0                           100                    0
              838860800                 2 ON        269923328                   0                           100                    0
              943718400                 2 ON        269923328                   0                           100                    0
             1048576000                 2 ON        269923328                   0                           100                    0
             1572864000                 3 ON        269923328                   0                           100                    0

PGA_TARGET_FOR_ESTIMATE PGA_TARGET_FACTOR ADV BYTES_PROCESSED ESTD_EXTRA_BYTES_RW ESTD_PGA_CACHE_HIT_PERCENTAGE ESTD_OVERALLOC_COUNT
----------------------- ----------------- --- --------------- ------------------- ----------------------------- --------------------
             2097152000                 4 ON        269923328                   0                           100                    0
             3145728000                 6 ON        269923328                   0                           100                    0
             4194304000                 8 ON        269923328                   0                           100                    0

14 rows selected.

SQL> show parameter pga

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
pga_aggregate_target                 big integer 500M
SQL>
SQL>
SQL>
SQL>
SQL>
SQL> select * from v$sysstat where name like '%work%';

   STATISTIC# NAME                                                                     CLASS         VALUE       STAT_ID
------------- ---------------------------------------------------------------- ------------- ------------- -------------
          180 no work - consistent read gets                                             128       2008286    2814375799
          332 workarea memory allocated                                                   64             0    2433935387
          333 workarea executions - optimal                                               64          5230    3211650785
          334 workarea executions - onepass                                               64             0     798730793
          335 workarea executions - multipass                                             64             0    3804491469

SQL> select * from v$sysstat where name like '%sort%';

   STATISTIC# NAME                                                                     CLASS         VALUE       STAT_ID
------------- ---------------------------------------------------------------- ------------- ------------- -------------
          349 sorts (memory)                                                              64          8463    2091983730
          350 sorts (disk)                                                                64             0    2533123502
          351 sorts (rows)                                                                64       2844652    3757672740

SQL>