摘要：如何给Large Delete操作提速近千倍？(五)
1.1. 第四次优化——使用FORALL 处理批量作业
上面我们已经介绍了批量作业的一些概念，这里不再赘述。
这次优化的思想主要是使用FORALL的思路来改写“第三次优化——拆分DELETE操作”，具体的修改如下：
SQL> l
1 create or replace procedure del_hubei_SSR_forall
2 as
3 type ridArray is table of rowid index by binary_integer;
4 type dtArray is table of varchar2(50) index by binary_integer;
5
6 v_rowid ridArray;
7 v_mid_to_delete dtArray;
8
9 begin
10 select mid,rowid bulk collect into v_mid_to_delete,v_rowid from temp_mid_hubei where rownum<11;
11
12 forall i in 1 .. v_mid_to_delete.COUNT
13 delete from SSR where mid = v_mid_to_delete(i);
14
15 DBMS_OUTPUT.PUT_LINE(’Full Finished!!!’);
16 DBMS_OUTPUT.PUT_LINE(’Totally ’||to_char(v_mid_to_delete.COUNT)||’ records deleted from hubei_SSR !!!’);
17
18 forall i in 1 .. v_rowid.COUNT
19 delete from temp_mid_hubei where rowid = v_rowid(i);
20
21 DBMS_OUTPUT.PUT_LINE(’Full Finished!!!’);
22 DBMS_OUTPUT.PUT_LINE(’Totally ’||to_char(v_rowid.COUNT)||’ records deleted from temp_mid_hubei !!!’);
23
24* end;
SQL> /
Procedure created.
Elapsed: 00:00:00.07
SQL>
SQL> exec del_hubei_SSR_forall;
Full Finished!!!
Totally 10 records deleted from hubei_SSR !!!
Full Finished!!!
Totally 10 records deleted from temp_mid_hubei !!!
PL/SQL procedure successfully completed.
Elapsed: 00:00:00.16
SQL>
这里应用了上面我们说过的SELECT BULK COLLECT INTO 方法来进行批量绑定，根据以10条记录为一组的测试结果表名，速度比较理想，于是再测1000条记录的情况：
SQL> exec del_hubei_SSR_forall;
Full Finished!!!
Totally 1000 records deleted from hubei_SSR !!!
Full Finished!!!
Totally 100 records deleted from temp_mid_hubei !!!
PL/SQL procedure successfully completed.
Elapsed: 00:00:00.66
SQL>
测试结果还是比较稳定，于是再测10000和100000条记录的情况：
SQL> exec del_hubei_SSR_forall;
Full Finished!!!
Totally 10000 records deleted from hubei_SSR !!!
Full Finished!!!
Totally 10000 records deleted from temp_mid_hubei !!!
PL/SQL procedure successfully completed.
Elapsed: 00:00:04.07
SQL>
SQL> exec del_hubei_SSR_forall;
Full Finished!!!
Totally 100000 records deleted from hubei_SSR !!!
Full Finished!!!
Totally 100000 records deleted from temp_mid_hubei !!!
PL/SQL procedure successfully completed.
Elapsed: 00:03:51.29
SQL>
这里我们注意到，完成删除10000记录需要4秒中，而完成100000条记录的删除需要将近4分钟，也就是说，从删除10000条记录到删除100000条记录，所需要的操作时间已经出现了比较大的倍数关系。
下面再测试一下50万条记录的情况：
SQL> exec del_hubei_SSR_forall;
Full Finished!!!
Totally 509555 records deleted from hubei_SSR !!!
Full Finished!!!
Totally 509555 records deleted from temp_mid_hubei !!!
PL/SQL procedure successfully completed.
Elapsed: 00:39:04.41
SQL>
这里，删除500000条记录已经需要将近40分钟了！
到这里，基本上可以得出结论，使用批量删除虽然可以解决一定的问题，但是如果需要操作的数组太大，那么执行结果会打打折扣，这个是不难理解的。
于是，第五次优化的思路就产生了：
1) 分段处理
2) 拆分操作
3) 批量绑定
