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这篇文章主要介绍了 oracle 如何使用 outline 固定执行计划事例，具有一定借鉴价值，感兴趣的朋友可以参考下，希望大家阅读完这篇文章之后大有收获，下面让丸趣 TV 小编带着大家一起了解一下。
1. 查看现在数据库等待事件
SQL select event,count(*) from v$session_wait group by event;
EVENT COUNT(*)
—————————————————————- ———-
SQL*Net message from client 85
SQL*Net message to client 1
buffer busy waits 3
db file scattered read 2
enqueue 1
pmon timer 1
rdbms ipc message 7
smon timer 1
8 rows selected.
对比之前的等待事件，enqueue，buffer busy waits 下降了很多
2. 查看下现在造成 enqueue 等待的 sql 语句
SQL SELECT DECODE(request,0, Holder: , Waiter:)|| sid sess, id1, id2,
lmode, request, type FROM V$LOCK WHERE (id1, id2, type) IN (SELECT id1,
id2, type FROM V$LOCK WHERE request 0) ORDER BY id1, request;
SESS ID1 ID2
LMODE REQUEST TYPE
———————————————— ———- ———-
———- ———- —-
Holder: 28 720940 432
6 0 TX
Waiter: 59 720940 432
0 6 TX
SQL SELECT /*+ ORDERED */ sql_text FROM v$sqltext a WHERE (a.hash_value,
a.address) IN (SELECT
DECODE(sql_hash_value,0,prev_hash_value,sql_hash_value),DECODE(sql_hash_value,0,prev_sql_addr,
sql_address) FROM v$session b WHERE b.sid = 28) ORDER BY piece ASC;
SQL_TEXT
—————————————————————-
update tab_test_sshz set jksj = :1 , clockfacktor = :2 where
yhsbh = :3 and skph = :4 and fplx_dm = :5
SQL /
SQL_TEXT
—————————————————————-
update tab_test_sshz set jksj = :1 , clockfacktor = :2 where
yhsbh = :3 and skph = :4 and fplx_dm = :5
过了几分钟再看等待事件
SQL /
EVENT COUNT(*)
—————————————————————- ———-
SQL*Net message from client 91
SQL*Net message to client 1
db file scattered read 1
db file sequential read 1
pmon timer 1
rdbms ipc message 7
smon timer 1
7 rows selected.
可以看到 enqueue，buffer busy waits 两个等待事件已经消失, 前面那条 update 语句
的阻塞已经自动释放掉了
在之前为以下 delete 语句阻塞了 update 语句
delete from tab_test_hz_zb a where exists(select y from tab_test_sshz b where a.kphzjs_id = b.kphzjs_id and b.skph = :1
and b.fplx_dm = :2 and b.kpqssj = TO_Date(:3, yyyy-mm-dd) )
update tab_test_sshz set jksj = :1 , clockfacktor = :2 where
yhsbh = :3 and skph = :4 and fplx_dm = :5
3. 查看之前经常发生阻塞的 sql 的执行计划
delete from SKSKJ.tab_test_hz_zb a
where exists (select y
from SKSKJ.tab_test_hz b
where a.kphzjs_id = b.kphzjs_id
and b.skph = :1
and b.fplx_dm = :2
and b.kpqssj = TO_Date(:3, yyyy-mm-dd))
PLAN_TABLE_OUTPUT
——————————————————————————————————————————————————————————————————–
————————————————————————————-
| Id | Operation | Name | Rows | Bytes
| Cost |
————————————————————————————-
| 0 | DELETE STATEMENT | | |
| |
| 1 | DELETE | tab_test_hz_ZB | |
| |
|* 2 | FILTER | | |
| |
| 3 | TABLE ACCESS FULL | tab_test_hz_ZB | |
| |
|* 4 | TABLE ACCESS BY INDEX ROWID| tab_test_hz | |
| |
|* 5 | INDEX UNIQUE SCAN | PKtab_test_hz | |
| |
————————————————————————————-
PLAN_TABLE_OUTPUT
——————————————————————————————————————————————————————————————————–
Predicate Information (identified by operation id):
—————————————————
2 – filter(EXISTS (SELECT 0 FROM SKSKJ . tab_test_hz B WHERE
B . KPHZJS_ID =:B1 AND B . KPQSSJ =TO_DATE(:Z, yyyy-mm-dd)
AND B . FPLX_DM =:Z
AND B . SKPH =:Z))
4 – filter(B . KPQSSJ =TO_DATE(:Z, yyyy-mm-dd) AND B . FPLX_DM =:Z
AND
B . SKPH =:Z)
5 – access(B . KPHZJS_ID =:B1)
PLAN_TABLE_OUTPUT
——————————————————————————————————————————————————————————————————–
Note: rule based optimization
23 rows selected.
这里发现 tab_test_hz_ZB 表为全表扫描,a.kphzjs_id 有索引, 并且数据库优化
器模式为 rule,
查询 oracle 文档得知, 在基于规则的优化器模式下,
如果 a.kphzjs_id = b.kphzjs_id，a.kphzjs_id 表达式作用了一个字段上，无论该字
段有无索引，RBO 都会全表扫描。
在 session 级别设置 CHOOSE 的优化器后 tab_test_hz_ZB 表走了索引
SQL alter session set optimizer_mode = CHOOSE;
Session altered.
SQL explain plan for
2 delete from SKSKJ.tab_test_hz_zb a
3 where exists (select y
4 from SKSKJ.tab_test_hz b
5 where a.kphzjs_id = b.kphzjs_id
6 and b.skph = :1
7 and b.fplx_dm = :2
8 and b.kpqssj = TO_Date(:3, yyyy-mm-dd
Explained.
SQL select plan_table_output from table(dbms_xplan.display());
PLAN_TABLE_OUTPUT
——————————————————————————————————————————————————————————————————–
——————————————————————————————
| Id | Operation | Name | Rows |
Bytes | Cost |
——————————————————————————————
| 0 | DELETE STATEMENT | | 1 |
101 | 11 |
| 1 | DELETE | tab_test_hz_ZB | |
| |
| 2 | NESTED LOOPS | | 1 |
101 | 11 |
| 3 | SORT UNIQUE | | |
| |
| 4 | TABLE ACCESS BY INDEX ROWID| tab_test_hz | 1 |
57 | 4 |
|* 5 | INDEX RANGE SCAN | C01$SKPH_FPLXDM_KPQSSJ | 1 |
| 3 |
|* 6 | INDEX RANGE SCAN | PKtab_test_hz_ZB | 1 |
44 | 2 |
PLAN_TABLE_OUTPUT
——————————————————————————————————————————————————————————————————–
——————————————————————————————
Predicate Information (identified by operation id):
—————————————————
5 – access(B . SKPH =:Z AND B . FPLX_DM =:Z AND
B . KPQSSJ =TO_DATE(:Z, yyyy-mm-dd))
6 – access(A . KPHZJS_ID = B . KPHZJS_ID)
Note: cpu costing is off
21 rows selected.
该数据库由于历史原因, 数据库优化器模式不能更改, 也不能修改程序使用 HINT 提示, 建议使用 outline 更改固定为走索引的执行计划
4. 固定执行计划方案如下:
4.1. 查看原来语句执行计划：
SQL explain plan for
delete from SKSKJ.tab_test_hz_zb a
where exists (select y
from SKSKJ.tab_test_hz b
where a.kphzjs_id = b.kphzjs_id
and b.skph = :1
and b.fplx_dm = :2
and b.kpqssj = TO_Date(:3, yyyy-mm-dd))
SQL select plan_table_output from table(dbms_xplan.display()); 查看原来语句
执行计划：
查看加了 hist 提示后走索引的执行计划
SQL explain plan for
2 delete from SKSKJ.tab_test_hz_zb a
3 where exists (select /*+ index(SKSKJ.tab_test_hz
C01$SKPH_FPLXDM_KPQSSJ ) */ y
4 from SKSKJ.tab_test_hz b
5 where a.kphzjs_id = b.kphzjs_id
6 and b.fplx_dm = :2
7 and b.skph = :1
8 and b.kpqssj = TO_Date(:3, yyyy-mm-dd
SQL select plan_table_output from table(dbms_xplan.display());
4.2. 创建 outlines
创建两个 public stroed outline，第一个是目前运行的，第二个是加了 hints.
create or replace outline tab_test_hz_zb_full on delete from
SKSKJ.tab_test_hz_zb a
where exists (select y
from SKSKJ.tab_test_hz b
where a.kphzjs_id = b.kphzjs_id
and b.skph = :1
and b.fplx_dm = :2
and b.kpqssj = TO_Date(:3, yyyy-mm-dd))
create or replace outline tab_test_hz_zb_index on delete from
SKSKJ.tab_test_hz_zb a
where exists (select /*+ index(SKSKJ.tab_test_hz C01$SKPH_FPLXDM_KPQSSJ
) */ y
from SKSKJ.tab_test_hz b
where a.kphzjs_id = b.kphzjs_id
and b.fplx_dm = :2
and b.skph = :1
and b.kpqssj = TO_Date(:3, yyyy-mm-dd
会话参数环境设置:
alter session set query_rewrite_enabled = true
alter session set star_transformation_enabled = true
当前模式下创建纲要表, 确保 OUTLN 用户存在:
exec dbms_outln_edit.create_edit_tables
为交换两个 stored outline 的执行计划做准备
create or replace private outline PRIV_tab_test_hz_ZB_F from
tab_test_hz_zb_full;
create or replace private outline PRIV_tab_test_hz_ZB_I from
tab_test_hz_zb_index;
– 必须和上面的命令使用同一个 session
UPDATE OL$HINTS
SET
OL_NAME=DECODE(OL_NAME, PRIV_tab_test_hz_ZB_F , PRIV_tab_test_hz_ZB_I , PRIV_tab_test_hz_ZB_I , PRIV_tab_test_hz_ZB_F)
WHERE OL_NAME IN (PRIV_tab_test_hz_ZB_F , PRIV_tab_test_hz_ZB_I
commit;
SQL set line 200
SQL select OL_name,HINT_TEXT from ol$hints;
— 刷新内存中的 outline 信息
alter session set use_private_outlines=true; 刷新
execute
dbms_outln_edit.refresh_private_outline(PRIV_tab_test_hz_ZB_F
execute
dbms_outln_edit.refresh_private_outline(PRIV_tab_test_hz_ZB_I 发布到
public outline
– 创建或更新 public outline
create or replace outline tab_test_hz_zb_full from private
PRIV_tab_test_hz_ZB_F;
create or replace outline tab_test_hz_zb_index from private
PRIV_tab_test_hz_ZB_I; 设置使用，调整完毕
alter system set use_stored_outlines=true; 启用 outlines
4.3 验证:
查看该语句执行计划是否为之前加了 hist 提示后走索引的执行计划, 如果使, 表示固定
执行计划成功
SQL explain plan for
delete from SKSKJ.tab_test_hz_zb a
where exists (select y
from SKSKJ.tab_test_hz b
where a.kphzjs_id = b.kphzjs_id
and b.skph = :1
and b.fplx_dm = :2
and b.kpqssj = TO_Date(:3, yyyy-mm-dd))
SQL select plan_table_output from table(dbms_xplan.display());
5 总结
5.1 可以先使用 outline 固定 delete 语句的执行计划走索引
5.2 由于 tab_test_sshz 表及 tab_test_hz_zb 表的 initrans=1，如果这两个表
访问比较频繁，建议调到 4 或者 5
5.3 目前数据库 db_cache_size=128M, 鉴于之前数据库缓慢时有大量 buffer busy
waits 等待，建议调大
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