Apress.Expert.Oracle.Database.Architecture.9i.and.10g.Programming.Techniques.and.Solutions.Sep.2005

CHAPTER 8 ■ TRANSACTIONS 267
Many people—for whatever reason—feel compelled to do it like this:
ops$tkyte@ORA10G> begin
2 for x in ( select rowid rid, object_name, rownum r
3 from t2 )
4 loop
5 update t2
6 set object_name = lower(x.object_name)
7 where rowid = x.rid;
8 if ( mod(x.r,100) = 0 ) then
9 commit;
10 end if;
11 end loop;
12 commit;
13 end;
14 /
PL/SQL procedure successfully completed.
Elapsed: 00:00:05.38
In this simple example, it is many times slower to commit frequently in a loop. If you
can do it in a single SQL statement, do it that way, as it is almost certainly faster. Even if we
“optimize” the procedural code, using bulk processing for the updates, as follows:
ops$tkyte@ORA10G> declare
2 type ridArray is table of rowid;
3 type vcArray is table of t2.object_name%type;
4
5 l_rids ridArray;
6 l_names vcArray;
7
8 cursor c is select rowid, object_name from t2;
9 begin
10 open c;
11 loop
12 fetch c bulk collect into l_rids, l_names LIMIT 100;
13 forall i in 1 .. l_rids.count
14 update t2
15 set object_name = lower(l_names(i))
16 where rowid = l_rids(i);
17 commit;
18 exit when c%notfound;
19 end loop;
20 close c;
21 end;
22 /
PL/SQL procedure successfully completed.
Elapsed: 00:00:02.36