如何使用pipeline function获得实时输出

来源：赛迪网    作者：Alizze

很多人都知道，在普通的函数中，使用dbms_output输出的信息，需要在服务器执行完整个函数后一次性的返回给客户端。但你如果需要在客户端实时的输出函数执行过程中的一些信息，在Oracle 9i以后则可以使用管道函数(pipeline function)。

PIPELINED（关键字）表明这是一个管道函数，管道函数的返回值类型必须为集合，在函数中，PIPE ROW语句被用来返回该集合的单个元素，函数则以一个空的RETURN语句结束，以表明它已经完成。

create or replace type MsgType as table of varchar2(4000);
/

create or replace function f_pipeline_test
return MsgType
PIPELINED
as
begin
    for i in 1 .. 10
    loop
        pipe row( 'Iteration ' || i || ' at ' || systimestamp );
        dbms_lock.sleep(1);
    end loop;
    pipe row( 'All done!' );
    return;
end;
/

在sql*plus中执行该函数，大家需要首先设置arraysize为1，否则服务器会按照默认的15来向客户端返回信息，这会影响我们的测试效果。

SQL> set arraysize 1
SQL> select * from table( f_pipeline_test );

COLUMN_VALUE
-----------------------------------------------------
Iteration 1 at 14-FEB-08 02.13.18.273988000 PM +08:00
Iteration 2 at 14-FEB-08 02.13.19.275988000 PM +08:00
Iteration 3 at 14-FEB-08 02.13.20.277767000 PM +08:00
Iteration 4 at 14-FEB-08 02.13.21.279591000 PM +08:00
Iteration 5 at 14-FEB-08 02.13.22.281366000 PM +08:00
Iteration 6 at 14-FEB-08 02.13.23.283189000 PM +08:00
Iteration 7 at 14-FEB-08 02.13.24.283965000 PM +08:00
Iteration 8 at 14-FEB-08 02.13.25.285785000 PM +08:00
Iteration 9 at 14-FEB-08 02.13.26.286570000 PM +08:00
Iteration 10 at 14-FEB-08 02.13.27.288387000 PM +08:00
All done!

11 rows selected.

如果要在pipeline中执行DML操作，则必须使用自治事务，否则会报ORA-14551错误

create or replace function f_pipeline_testdml
return MsgType
PIPELINED
as
begin
    for i in 1 .. 10
    loop
        insert into test values(1);
        pipe row( 'insert into test values( ' || i || ') success at ' || systimestamp );
        dbms_lock.sleep(1);
    end loop;
    pipe row( 'All done!' );
    return;
end;
/

SQL>  select * from table( f_pipeline_testdml );
 select * from table( f_pipeline_testdml )
                      *
ERROR at line 1:
ORA-14551: cannot perform a DML operation inside a query
ORA-06512: at "NING.F_PIPELINE_TESTDML", line 8
create or replace function f_pipeline_testdml
return MsgType
PIPELINED
as
pragma autonomous_transaction;
begin
for i in 1 .. 10
loop
insert into test values(1);
commit;
pipe row( 'insert values ' || i || ' success at ' || systimestamp );
dbms_lock.sleep(1);
end loop;
pipe row( 'All done!' );
return;
end;
/

SQL> select * from table( f_pipeline_testdml );

COLUMN_VALUE
--------------------------------------------------------------------------------
insert values  1  success at 14-FEB-08 02.16.47.855158000 PM +08:00
insert values  2  success at 14-FEB-08 02.16.48.865559000 PM +08:00
insert values  3  success at 14-FEB-08 02.16.49.867377000 PM +08:00
insert values  4  success at 14-FEB-08 02.16.50.873154000 PM +08:00
insert values  5  success at 14-FEB-08 02.16.51.874942000 PM +08:00
insert values  6  success at 14-FEB-08 02.16.52.880781000 PM +08:00
insert values  7  success at 14-FEB-08 02.16.53.882543000 PM +08:00
insert values  8  success at 14-FEB-08 02.16.54.894348000 PM +08:00
insert values  9  success at 14-FEB-08 02.16.55.896153000 PM +08:00
insert values  10 success at 14-FEB-08 02.16.56.901904000 PM +08:00
All done!

11 rows selected.

在Oracle 9205及其之后的版本中，在pipeline function中使用自治事务，则必须在pipe row之前提交或者回滚事务，否则会报ORA-06519错误。

create or replace function f_pipeline_testdml
return MsgType
PIPELINED
as
pragma autonomous_transaction;
begin
for i in 1 .. 10
loop
insert into test values(1);
pipe row( 'insert values ' || i || ' success at ' || systimestamp );
dbms_lock.sleep(1);
end loop;
pipe row( 'All done!' );
commit;
return;
end;
/

SQL> select * from table( f_pipeline_testdml );
select * from table( f_pipeline_testdml )
                     *
ERROR at line 1:
ORA-06519: active autonomous transaction detected and rolled back
ORA-06512: at "NING.F_PIPELINE_TESTDML", line 10

此处是由于在9205中修复Bug 2711518导致了自治事务的行为有所改变。如果系统从9205之前的版本升级到之后的版本，需要保证pipeline function的行为和以前版本一致，Oracle提供了一个10946事件来设置和以前版本的兼容性，如果在管道函数中使用了select for update的cursor，则必须设置event回归以前的特性，否则即使在pipe row之前commit也会导致出现ORA-1002错误。

ALTER SYSTEM SET EVENT = "10946 trace name context forever, level 8" scope=spfile;