并行进程

SQL> show parameter parallel_min

 

NAME                     TYPE    VALUE

------------------------------------ ----------- ------------------------------

parallel_min_percent             integer 0

 

SQL> show parameter parallel_max

 

NAME                     TYPE    VALUE

------------------------------------ ----------- ------------------------------

parallel_max_servers             integer 960

 

SQL> select * from v$px_process_sysstat;

 

STATISTIC                             VALUE

------------------------------------------------------------ ----------

Servers In Use                                0

Servers Available                            64

Servers Started                             308

Servers Shutdown                            244

Servers Highwater                            64

Servers Cleaned Up                            0

Server Sessions                          226823

Memory Chunks Allocated                         105

Memory Chunks Freed                          87

Memory Chunks Current                            18

Memory Chunks HWM                            23

 

STATISTIC                             VALUE

------------------------------------------------------------ ----------

Buffers Allocated                       1771708

Buffers Freed                           1771708

Buffers Current                               0

Buffers HWM                            1566

 

15 rows selected.

 

Servers In Use: 正在使用的并行进程的数量

 

Servers Available:可用的并行进程的数量

 

执行SQL:

SQL> select /*+ parallel(a 8)*/ count(*) from T_PM_ACCT_DTL a;

对应8个进程

祖宗进程为384

那么加上group by 和order by呢？

SQL> select /*+ parallel(a 8)*/ count(*) from T_PM_ACCT_DTL a group by a.data_date order by a.data_date;

可以看到已经使用了16个