在工作中使用並行可以極大的提高工作效率。可以Object,session.hint級別引入並行。可以使大量的資料處理更加高效。

比如現在有一個表 t 有1000萬行，如果想以這個表為基礎，把資料選擇性的插入另外一個表t2，
使用Insert into t2 select *from t;
使用並行來處理也沒有問題，但是如果使用dbms_parallel_execute也是一種很不錯的選擇。
使用dbms_parallel_execute的實現方式和parallel還有一定的差別。
這個包在11g開始引入，可能初次接觸的時候會被它大量的功能所淹沒，不知道從何開始。

舉個例子來說明一下。
我們建立一個表 t，限於環境的情況，目前做一個百萬級別的資料dml操作，使用dbms_parallel_execute來完成。
建立表t.

SQL> drop table t;

Table dropped.

SQL> create table t as select object_id,object_name from dba_objects;

Table created.

建立表t2,我們專門專門多加了一個欄位。session_id。到時候會有用處。

SQL> drop table t2;

Table dropped.

SQL> create table t2 as select t1.*,0 session_id from t t1 where 1=0;

Table created.

使用如下的儲存過程來模擬一個dml的處理過程。傳入的引數，是根據rowid來處理。
create or replace procedure serial(p_lo_rid in rowid,p_hi_rid in rowid)
is
begin
for x in (select object_id object_id,object_name object_name from t where rowid between p_lo_rid and p_hi_rid)
loop
insert into t2(object_id,object_name,session_id)
values(x.object_id,x.object_name,sys_context('userenv','sessionid'));
end loop;
end;
/

使用dbms_parallel_execute來建立一個Job,以1萬條資料分單位進行資料的rowid切分。

begin
dbms_parallel_execute.create_task('PROCESS TASK');
dbms_parallel_execute.create_chunks_by_rowid
( task_name=>'PROCESS TASK',
table_owner=>user,
table_name=>'T',
by_row=>false,
chunk_size=>10000);
end;
/

透過dba_parallel_execute_chunks可以檢視到切分後的rowid情況。

set pages 200
select *from (
select chunk_id,status,start_rowid,end_rowid
from dba_parallel_execute_chunks
where task_name='PROCESS TASK'
order by chunk_id
);

檢視切分後的情況，我們可以把切分後的每一個子塊稱為chunk。可以透過這個語句來簡單的監控進度。
CHUNK_ID STATUS               START_ROWID        END_ROWID
---------- -------------------- ------------------ ------------------
       600 UNASSIGNED           AAAEQCAAFAAAACAAAA AAAEQCAAFAAAAD/CcP
       601 UNASSIGNED           AAAEQCAAFAAAAEAAAA AAAEQCAAFAAAAF/CcP
       602 UNASSIGNED           AAAEQCAAFAAAAGAAAA AAAEQCAAFAAAAH/CcP
       603 UNASSIGNED           AAAEQCAAFAAAAIAAAA AAAEQCAAFAAAAJ/CcP
       604 UNASSIGNED           AAAEQCAAFAAAAKAAAA AAAEQCAAFAAAAL/CcP
       605 UNASSIGNED           AAAEQCAAFAAAAWAAAA AAAEQCAAFAAAAX/CcP
       606 UNASSIGNED           AAAEQCAAFAAAAYAAAA AAAEQCAAFAAAAZ/CcP
       607 UNASSIGNED           AAAEQCAAFAAAAaAAAA AAAEQCAAFAAAAb/CcP
       608 UNASSIGNED           AAAEQCAAFAAAAcAAAA AAAEQCAAFAAAAd/CcP
       609 UNASSIGNED           AAAEQCAAFAAAEsYAAA AAAEQCAAFAAAEsfCcP
       610 UNASSIGNED           AAAEQCAAFAAAEsgAAA AAAEQCAAFAAAEsnCcP

可以使用如下的部分來開始處理資料。啟用了4個並行，並行度可以情況來提高。:start_id,:end_id是上面對應的rowid.

begin
dbms_parallel_execute.run_task
(task_name=>'PROCESS TASK',
sql_stmt=>'begin serial(:start_id,:end_id); end;',
language_flag=>DBMS_SQL.NATIVE,
parallel_level=>4);
end;
/

select *from (
select chunk_id,status,start_rowid,end_rowid
from dba_parallel_execute_chunks
where task_name='PROCESS TASK'
order by chunk_id
);

資料處理的進度可以檢視得到。
CHUNK_ID STATUS               START_ROWID        END_ROWID
---------- -------------------- ------------------ ------------------
       600 PROCESSED            AAAEQCAAFAAAACAAAA AAAEQCAAFAAAAD/CcP
       601 PROCESSED            AAAEQCAAFAAAAEAAAA AAAEQCAAFAAAAF/CcP
       602 PROCESSED            AAAEQCAAFAAAAGAAAA AAAEQCAAFAAAAH/CcP
       603 PROCESSED            AAAEQCAAFAAAAIAAAA AAAEQCAAFAAAAJ/CcP
       604 PROCESSED            AAAEQCAAFAAAAKAAAA AAAEQCAAFAAAAL/CcP
       605 PROCESSED            AAAEQCAAFAAAAWAAAA AAAEQCAAFAAAAX/CcP
       606 PROCESSED            AAAEQCAAFAAAAYAAAA AAAEQCAAFAAAAZ/CcP
       607 PROCESSED            AAAEQCAAFAAAAaAAAA AAAEQCAAFAAAAb/CcP
       608 PROCESSED            AAAEQCAAFAAAAcAAAA AAAEQCAAFAAAAd/CcP

處理完資料之後，就可以刪除這個job了。

begin
dbms_parallel_execute.drop_task('PROCESS TASK');
end;
/

我們可以在t2的新增列中看到每個對應的parallel處理的資料情況，可以看到資料的處理還是很平均的。
select session_id,count(*)
from t2
group by session_id
order by session_id;

SESSION_ID   COUNT(*)
---------- ----------
   1670371     357834
   1670372     370487
   1670373     403604
   1670374     404679

在資料處理的時候。可以看到dbms_parallel_execute後臺啟用的處理程式和並行還是有一些不同的。
啟用了4個並行之後，看到都是j00這樣的程式。

top - 06:31:03 up 1 day, 5:21, 2 users, load average: 3.97, 1.55, 0.61
Tasks: 167 total,   4 running, 163 sleeping,   0 stopped,   0 zombie
Cpu(s): 60.7%us, 7.7%sy, 0.0%ni, 1.0%id, 28.9%wa, 0.2%hi, 1.5%si, 0.0%st
Mem:   2030124k total, 1293220k used,   736904k free,   358400k buffers
Swap: 4063224k total,        0k used, 4063224k free,   476552k cached

PID USER      PR NI VIRT RES SHR S %CPU %MEM    TIME+ COMMAND
32630 ora11g    20   0 530m 67m 64m D 55.2 3.4   0:48.34 ora_j000_TEST01
32634 ora11g    20   0 529m 60m 57m R 38.4 3.0   0:46.88 ora_j002_TEST01
32632 ora11g    20   0 529m 62m 59m R 24.8 3.2   0:44.54 ora_j001_TEST01
32636 ora11g    20   0 529m 59m 56m R 17.5 3.0   0:44.88 ora_j003_TEST01
2295 ora11g    20   0 541m 79m 67m D 1.3 4.0   0:11.93 ora_dbw0_TEST01
32706 ora11g    20   0 14940 1240 904 R 1.0 0.1   0:00.39 top -c
825 root      20   0     0    0    0 S 0.3 0.0   0:18.85 [jbd2/sdb3-8]

如果調高parallel從4到16，可以看到j00的程式相應的增加了。

top - 06:32:59 up 1 day, 5:23, 2 users, load average: 1.31, 1.29, 0.63
Tasks: 182 total,   4 running, 178 sleeping,   0 stopped,   0 zombie
Cpu(s): 77.2%us, 21.2%sy, 0.0%ni, 1.2%id, 0.2%wa, 0.0%hi, 0.2%si, 0.0%st
Mem:   2030124k total, 1345284k used,   684840k free,   358500k buffers
Swap: 4063224k total,        0k used, 4063224k free,   476800k cached

PID USER      PR NI VIRT RES SHR S %CPU %MEM    TIME+ COMMAND
404 ora11g    20   0 530m 39m 36m R 23.4 2.0   0:01.75 ora_j010_TEST01
392 ora11g    20   0 529m 33m 30m S 17.1 1.7   0:01.39 ora_j004_TEST01
402 ora11g    20   0 529m 31m 28m R 16.1 1.6   0:00.86 ora_j009_TEST01
384 ora11g    20   0 530m 35m 32m S 12.2 1.8   0:01.21 ora_j000_TEST01
386 ora11g    20   0 529m 32m 29m S 11.9 1.6   0:01.11 ora_j001_TEST01
422 root      20   0 122m 19m 10m S 11.5 1.0   0:00.35 /u04/app/11.2.0/grid/bin/crsctl.bin check has
394 ora11g    20   0 529m 31m 29m S 10.5 1.6   0:00.86 ora_j005_TEST01
410 ora11g    20   0 530m 31m 28m R 10.5 1.6   0:00.63 ora_j013_TEST01
408 ora11g    20   0 529m 32m 29m S 9.6 1.6   0:00.93 ora_j012_TEST01
388 ora11g    20   0 529m 32m 29m S 8.9 1.6   0:01.14 ora_j002_TEST01
398 ora11g    20   0 530m 32m 29m S 8.6 1.6   0:00.98 ora_j007_TEST01
390 ora11g    20   0 529m 31m 28m S 7.6 1.6   0:00.74 ora_j003_TEST01
396 ora11g    20   0 529m 32m 29m S 7.2 1.6   0:01.04 ora_j006_TEST01
406 ora11g    20   0 530m 30m 27m S 5.6 1.5   0:00.49 ora_j011_TEST01
414 ora11g    20   0 529m 29m 26m S 5.6 1.5   0:00.45 ora_j015_TEST01
400 ora11g    20   0 529m 30m 27m S 4.9 1.5   0:00.64 ora_j008_TEST01
412 ora11g    20   0 530m 30m 27m S 4.6 1.5   0:00.63 ora_j014_TEST01

使用dbms_parallel_execute來完成DML的並行

相關文章