[英]Oracle SQL - Query Time Limit
以類似的方式
select * from mytable where rownum <= 1000;
會給我查詢結果的前1000行,有沒有辦法
select * from mytable where runtime <= 1000;
哪個將返回在運行查詢的前1000個<時間單位>中獲得的結果?
Oracle不支持此功能 ,至少在您的示例中並不容易。
我發現一個博客能夠限制用戶在特定資源組中的執行時間。 他們為上述用戶創建了一個特殊的組,然后他們為該用戶定義了一個資源計划,稱為LIMIT_EXEC_TIME
。 其代碼如下,以供參考:
set serverout on size 5555
--
-- first remove an existing active plan
ALTER SYSTEM SET RESOURCE_MANAGER_PLAN ='';
--
-- delete any existing plan or group
-- we have to create a pending area first
exec dbms_resource_manager.clear_pending_area();
exec dbms_resource_manager.create_pending_area();
exec dbms_resource_manager.DELETE_PLAN ('LIMIT_EXEC_TIME');
exec dbms_resource_manager.DELETE_CONSUMER_GROUP ('GROUP_WITH_LIMITED_EXEC_TIME');
exec DBMS_RESOURCE_MANAGER.VALIDATE_PENDING_AREA;
exec DBMS_RESOURCE_MANAGER.SUBMIT_PENDING_AREA();
begin
dbms_resource_manager.create_pending_area();
--
-- we need a consumer group that maps to the desired oracle user:
dbms_resource_manager.create_consumer_group(
CONSUMER_GROUP=>'GROUP_WITH_LIMITED_EXEC_TIME',
COMMENT=>'This is the consumer group that has limited execution time per statement'
);
dbms_resource_manager.set_consumer_group_mapping(
attribute => DBMS_RESOURCE_MANAGER.ORACLE_USER,
value => 'PYTHIAN',
consumer_group =>'GROUP_WITH_LIMITED_EXEC_TIME'
);
-- and we need a resource plan:
dbms_resource_manager.create_plan(
PLAN=> 'LIMIT_EXEC_TIME',
COMMENT=>'Kill statement after exceeding total execution time'
);
-- now let's create a plan directive for that special user group
-- the plan will cancel the current SQL if it runs for more than 120 sec
dbms_resource_manager.create_plan_directive(
PLAN=> 'LIMIT_EXEC_TIME',
GROUP_OR_SUBPLAN=>'GROUP_WITH_LIMITED_EXEC_TIME',
COMMENT=>'Kill statement after exceeding total execution time',
SWITCH_GROUP=>'CANCEL_SQL',
SWITCH_TIME=>15,
SWITCH_ESTIMATE=>false
);
dbms_resource_manager.create_plan_directive(
PLAN=> 'LIMIT_EXEC_TIME',
GROUP_OR_SUBPLAN=>'OTHER_GROUPS',
COMMENT=>'leave others alone',
CPU_P1=>100
);
DBMS_RESOURCE_MANAGER.VALIDATE_PENDING_AREA;
DBMS_RESOURCE_MANAGER.SUBMIT_PENDING_AREA();
end;
/
exec dbms_resource_manager_privs.grant_switch_consumer_group('PYTHIAN','GROUP_WITH_LIMITED_EXEC_TIME',false);
exec dbms_resource_manager.set_initial_consumer_group('PYTHIAN','GROUP_WITH_LIMITED_EXEC_TIME');
select * from DBA_RSRC_CONSUMER_GROUPS;
select * from DBA_RSRC_GROUP_MAPPINGS;
select * from DBA_RSRC_PLANS;
select * from DBA_RSRC_PLAN_DIRECTIVES;
-- to enable it:
ALTER SYSTEM SET RESOURCE_MANAGER_PLAN ='LIMIT_EXEC_TIME';
SELECT se.sid sess_id, co.name consumer_group,
se.state, se.consumed_cpu_time cpu_time, se.cpu_wait_time, se.queued_time
FROM v$rsrc_session_info se, v$rsrc_consumer_group co
WHERE se.current_consumer_group_id = co.id;
select username,resource_CONSUMER_GROUP,count(*) from v$session group by username,resource_CONSUMER_GROUP;
部分結果
查詢可以返回部分結果,但查詢還會引發異常“ ORA-00040:超出活動時間限制-調用已中止”,客戶端必須忽略該異常。
這可以通過執行大量CPU工作的函數來模擬:
create or replace function sleep_cpu return number authid current_user is
v_loop number := 0;
begin
for i in 1 .. 10000000 loop
v_loop := v_loop + 1;
end loop;
return v_loop;
end;
/
SQL * Plus可以證明客戶端能夠讀取部分結果:
SQL> set timing on
SQL> select sleep_cpu()
2 from dual
3 connect by level <= 100;
SLEEP_CPU()
-----------
10000000
10000000
10000000
10000000
10000000
10000000
10000000
10000000
10000000
10000000
10000000
10000000
10000000
10000000
10000000
ERROR:
ORA-00040: active time limit exceeded - call aborted
15 rows selected.
Elapsed: 00:00:08.52
SQL>
請注意,在此示例中,經過時間為8秒。 我將超時設置為5秒,這表明很難獲得良好的精度。
CPU時間,未用時間
資源管理器僅計算CPU時間,而不計算經過時間。 盡管有文檔說明,但是這是正確的。 Pythian文章中的評論之一表明,可以使用ALTER SYSTEM SET EVENT = '10720 trace name context forever, level 16384' scope=spfile;
來更改此行為ALTER SYSTEM SET EVENT = '10720 trace name context forever, level 16384' scope=spfile;
(和重新啟動),但這對我不起作用。
例如,創建以下函數:
create or replace function sleep_no_cpu return number authid current_user is
begin
execute immediate 'begin dbms_lock.sleep(1); end;';
return 1;
end;
/
此SELECT將運行整個100秒,因為它沒有使用100秒的CPU。
select sleep_cpu()
from dual
connect by level <= 100;
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