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最近，oracle rac维护中遇到一件很奇怪的事情，就是业务偶尔会出现极其缓慢的情况，查看服务器负载、数据库负载却很低，数据库和主机日志也没有明显报错，数据库内部也没有拥堵会话的情况。本文特此记录，以备后查！
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背景： 从12月份开始，应用开始反馈，没次做新品发布，下发单据就会特别慢，后来为了临时解决问题，将业务指向到单节点，发现业务下发速度恢复正常。后来，过了一周左右的时间，单据下发速度再次很慢。但是， 查看服务器负载、数据库负载却很低，数据库和主机日志也没有明显报错，数据库内部也没有拥堵会话的情况。为了尽快恢复业务，重启了数据库服务，
业务暂时恢复正常。然而，三四天之后，也就是今天，又出现下发单据缓慢的情况。
问题分析：
1、基于以上背景，数据库和主机没有高负载，尤其是数据库内部没有会话拥堵的情况，我能想到的是SQL执行计划可能出现了变化。
2、查看业务承载节点，在执行的SQL语句
3、查看sql-5216pwt38ckhp的执行计划
--优秀的执行计划，一次单据下发3-8点能执行近30次
--变化后的低效执行计划，一次单据下发3-10点，执行只有1完多次
4、通过步骤3中变化前后的执行计划对比，我们发现
--变化前的执行计划走的主键唯一索引扫描，变化后的执行计划走的普通索引的范围扫描
--变化前的执行计划buffer get很低为11，且没有磁盘读，变化后的执行计划buffer很高为28万，出现了磁盘物理读
--变化前的执行计划唯一索引扫描后回表扫描一行数据，变化后的执行计划对索引全分区扫描后回表扫描一行数据
--变化前的执行计划单次单据下发3-8点能执行近30完成，变化后的执行计划单次单据下发3-10点才执行1万多次
问题处理：
基于以上问题分析，SQL-5216pwt38ckhp语句是update语句，且使用了绑定变量，因此，在不改变sql的情况下，我们
选择固定sql的执行计划。方法是使用脚本coe_load_sql_profile.sql进行执行计划固定，在执行计划固定的时候需要注意，
不能以sys登陆数据库执行固话执行计划，需要使用业务用户执行，固话过程中，需要输入两次sql_id，然后选择优异执行计划的plan hash value即可。
附上执行计划固定脚本coe_load_sql_profile.sql：
SPO coe_load_sql_profile.log;
SET DEF ON TERM OFF ECHO ON FEED OFF VER OFF HEA ON LIN 2000 PAGES 100 LONG 8000000 LONGC 800000 TRIMS ON TI OFF TIMI OFF SERVEROUT ON SIZE 1000000 NUM 20 SQLP SQL>;
SET SERVEROUT ON SIZE UNL;
REM
REM $Header: 215187.1 coe_load_sql_profile.sql 11.4.5.5 2013/03/01 carlos.sierra $
REM
REM Copyright (c) 2000-2013, Oracle Corporation. All rights reserved.
REM
REM AUTHOR
REM carlos.sierra@oracle.com
REM
REM SCRIPT
REM coe_load_sql_profile.sql
REM
REM DESCRIPTION
REM This script loads a plan from a modified SQL into a Custom SQL
REM Profile for the original SQL.
REM If a good performing plan only reproduces with CBO Hints
REM then you can load the plan of the modified version of the
REM SQL into a Custom SQL Profile for the orignal SQL.
REM In other words, the original SQL can use the plan that was
REM generated out of the SQL with hints.
REM
REM PRE-REQUISITES
REM 1. Have in cache or AWR the text for the original SQL.
REM 2. Have in cache or AWR the plan for the modified SQL
REM (usually with hints).
REM
REM PARAMETERS
REM 1. ORIGINAL_SQL_ID (required)
REM 2. MODIFIED_SQL_ID (required)
REM 3. PLAN_HASH_VALUE (required)
REM
REM EXECUTION
REM 1. Connect into SQL*Plus as user with access to data dictionary
REM and privileges to create SQL Profiles. Do not use SYS.
REM 2. Execute script coe_load_sql_profile.sql passing first two
REM parameters inline or until requested by script.
REM 3. Provide plan hash value of the modified SQL when asked.
REM 4. Use a DBA user but not SYS. Do not connect as SYS as the staging
REM table cannot be created in SYS schema and you will receive an error:
REM ORA-19381: cannot create staging table in SYS schema
REM
REM EXAMPLE
REM # sqlplus system
REM SQL> START coe_load_sql_profile.sql gnjy0mn4y9pbm b8f3mbkd8bkgh
REM SQL> START coe_load_sql_profile.sql;
REM
REM NOTES
REM 1. This script works on 10g or higher.
REM 2. For a similar script for 11g use coe_load_sql_baseline.sql,
REM which uses SQL Plan Baselines instead of Custom SQL Profiles.
REM 3. For possible errors see coe_load_sql_profile.log
REM 4. If you get "ORA-06532: Subscript outside of limit, ORA-06512: at line 1"
REM Then you may consider this change (only in a test and disposable system):
REM create or replace TYPE sys.sqlprof_attr AS VARRAY(5000) of VARCHAR2(500);
REM
SET TERM ON ECHO OFF;
PRO
PRO Parameter 1:
PRO ORIGINAL_SQL_ID (required)
PRO
DEF original_sql_id = '&1';
PRO
PRO Parameter 2:
PRO MODIFIED_SQL_ID (required)
PRO
DEF modified_sql_id = '&2';
PRO
WITH
p AS (
SELECT plan_hash_value
FROM gv$sql_plan
WHERE sql_id = TRIM('&&modified_sql_id.')
AND other_xml IS NOT NULL
UNION
SELECT plan_hash_value
FROM dba_hist_sql_plan
WHERE sql_id = TRIM('&&modified_sql_id.')
AND other_xml IS NOT NULL ),
m AS (
SELECT plan_hash_value,
SUM(elapsed_time)/SUM(executions) avg_et_secs
FROM gv$sql
WHERE sql_id = TRIM('&&modified_sql_id.')
AND executions > 0
GROUP BY
plan_hash_value ),
a AS (
SELECT plan_hash_value,
SUM(elapsed_time_total)/SUM(executions_total) avg_et_secs
FROM dba_hist_sqlstat
WHERE sql_id = TRIM('&&modified_sql_id.')
AND executions_total > 0
GROUP BY
plan_hash_value )
SELECT p.plan_hash_value,
ROUND(NVL(m.avg_et_secs, a.avg_et_secs)/1e6, 3) avg_et_secs
FROM p, m, a
WHERE p.plan_hash_value = m.plan_hash_value(+)
AND p.plan_hash_value = a.plan_hash_value(+)
ORDER BY
avg_et_secs NULLS LAST;
PRO
PRO Parameter 3:
PRO PLAN_HASH_VALUE (required)
PRO
DEF plan_hash_value = '&3';
PRO
PRO Values passed to coe_load_sql_profile:
PRO ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PRO ORIGINAL_SQL_ID: "&&original_sql_id."
PRO MODIFIED_SQL_ID: "&&modified_sql_id."
PRO PLAN_HASH_VALUE: "&&plan_hash_value."
PRO
WHENEVER SQLERROR EXIT SQL.SQLCODE;
SET TERM OFF ECHO ON;
-- trim parameters
COL original_sql_id NEW_V original_sql_id FOR A30;
COL modified_sql_id NEW_V modified_sql_id FOR A30;
COL plan_hash_value NEW_V plan_hash_value FOR A30;
SELECT TRIM('&&original_sql_id.') original_sql_id, TRIM('&&modified_sql_id.') modified_sql_id, TRIM('&&plan_hash_value.') plan_hash_value FROM DUAL;
-- open log file
SPO coe_load_sql_profile_&&original_sql_id..log;
GET coe_load_sql_profile.log;
.
-- get user
COL connected_user NEW_V connected_user FOR A30;
SELECT USER connected_user FROM DUAL;
VAR sql_text CLOB;
VAR other_xml CLOB;
VAR signature NUMBER;
VAR name VARCHAR2(30);
EXEC :sql_text := NULL;
EXEC :other_xml := NULL;
EXEC :signature := NULL;
EXEC :name := NULL;
-- get sql_text from memory
DECLARE
l_sql_text VARCHAR2(32767);
BEGIN -- 10g see bug 5017909
FOR i IN (SELECT DISTINCT piece, sql_text
FROM gv$sqltext_with_newlines
WHERE sql_id = TRIM('&&original_sql_id.')
ORDER BY 1, 2)
LOOP
IF :sql_text IS NULL THEN
DBMS_LOB.CREATETEMPORARY(:sql_text, TRUE);
DBMS_LOB.OPEN(:sql_text, DBMS_LOB.LOB_READWRITE);
END IF;
l_sql_text := REPLACE(i.sql_text, CHR(00), ' ');
DBMS_LOB.WRITEAPPEND(:sql_text, LENGTH(l_sql_text), l_sql_text);
END LOOP;
IF :sql_text IS NOT NULL THEN
DBMS_LOB.CLOSE(:sql_text);
END IF;
EXCEPTION
WHEN OTHERS THEN
DBMS_OUTPUT.PUT_LINE('getting original sql_text from memory: '||SQLERRM);
:sql_text := NULL;
END;
/
-- get sql_text from awr
BEGIN
IF :sql_text IS NULL OR NVL(DBMS_LOB.GETLENGTH(:sql_text), 0) = 0 THEN
SELECT REPLACE(sql_text, CHR(00), ' ')
INTO :sql_text
FROM dba_hist_sqltext
WHERE sql_id = TRIM('&&original_sql_id.')
AND sql_text IS NOT NULL
AND ROWNUM = 1;
END IF;
EXCEPTION
WHEN OTHERS THEN
DBMS_OUTPUT.PUT_LINE('getting original sql_text from awr: '||SQLERRM);
:sql_text := NULL;
END;
/
-- sql_text as found
SELECT :sql_text FROM DUAL;
-- check is sql_text for original sql is available
SET TERM ON;
BEGIN
IF :sql_text IS NULL THEN
RAISE_APPLICATION_ERROR(-20100, 'SQL_TEXT for original SQL_ID &&original_sql_id. was not found in memory (gv$sqltext_with_newlines) or AWR (dba_hist_sqltext).');
END IF;
END;
/
SET TERM OFF;
-- get other_xml from memory
BEGIN
FOR i IN (SELECT other_xml
FROM gv$sql_plan
WHERE sql_id = TRIM('&&modified_sql_id.')
AND plan_hash_value = TO_NUMBER(TRIM('&&plan_hash_value.'))
AND other_xml IS NOT NULL
ORDER BY
child_number, id)
LOOP
:other_xml := i.other_xml;
EXIT; -- 1st
END LOOP;
EXCEPTION
WHEN OTHERS THEN
DBMS_OUTPUT.PUT_LINE('getting modified other_xml from memory: '||SQLERRM);
:other_xml := NULL;
END;
/
-- get other_xml from awr
BEGIN
IF :other_xml IS NULL OR NVL(DBMS_LOB.GETLENGTH(:other_xml), 0) = 0 THEN
FOR i IN (SELECT other_xml
FROM dba_hist_sql_plan
WHERE sql_id = TRIM('&&modified_sql_id.')
AND plan_hash_value = TO_NUMBER(TRIM('&&plan_hash_value.'))
AND other_xml IS NOT NULL
ORDER BY
id)
LOOP
:other_xml := i.other_xml;
EXIT; -- 1st
END LOOP;
END IF;
EXCEPTION
WHEN OTHERS THEN
DBMS_OUTPUT.PUT_LINE('getting modified other_xml from awr: '||SQLERRM);
:other_xml := NULL;
END;
/
-- other_xml as found
SELECT :other_xml FROM DUAL;
-- validate other_xml
SET TERM ON;
BEGIN
IF :other_xml IS NULL THEN
RAISE_APPLICATION_ERROR(-20101, 'PLAN for modified SQL_ID &&modified_sql_id. and PHV &&plan_hash_value. was not found in memory (gv$sql_plan) or AWR (dba_hist_sql_plan).');
END IF;
END;
/
SET ECHO OFF;
DECLARE
h SYS.SQLPROF_ATTR := SYS.SQLPROF_ATTR ();
idx INTEGER := 0;
l_pos NUMBER;
l_hint VARCHAR2(32767);
description VARCHAR2(500);
PROCEDURE add_hint (p_hint IN VARCHAR2)
IS
BEGIN
idx := idx + 1;
DBMS_OUTPUT.PUT_LINE(LPAD(idx, 4, '0')||' '||p_hint);
h.EXTEND;
h(idx) := p_hint;
END add_hint;
BEGIN
add_hint('BEGIN_OUTLINE_DATA');
FOR i IN (SELECT /*+ opt_param('parallel_execution_enabled', 'false') */
SUBSTR(EXTRACTVALUE(VALUE(d), '/hint'), 1, 4000) hint
FROM TABLE(XMLSEQUENCE(EXTRACT(XMLTYPE(:other_xml), '/*/outline_data/hint'))) d)
LOOP
l_hint := i.hint;
WHILE NVL(LENGTH(l_hint), 0) > 0
LOOP
IF LENGTH(l_hint) <= 500 THEN
add_hint(l_hint);
l_hint := NULL;
ELSE
l_pos := INSTR(SUBSTR(l_hint, 1, 500), ' ', -1);
add_hint(SUBSTR(l_hint, 1, l_pos));
l_hint := ' '||SUBSTR(l_hint, l_pos);
END IF;
END LOOP;
END LOOP;
add_hint('END_OUTLINE_DATA');
:signature := DBMS_SQLTUNE.SQLTEXT_TO_SIGNATURE(:sql_text);
:name := UPPER(TRIM('&&original_sql_id.'))||'_'||TRIM('&&plan_hash_value.');
description := UPPER('original:'||TRIM('&&original_sql_id.')||' modified:'||TRIM('&&modified_sql_id.')||' phv:'||TRIM('&&plan_hash_value.')||' signature:'||:signature||' created by coe_load_sql_profile.sql');
-- create custom sql profile for original sql using plan from modified sql
DBMS_SQLTUNE.IMPORT_SQL_PROFILE (
sql_text => :sql_text, -- original sql
profile => h, -- plan from modified sql
name => :name,
description => description,
category => 'DEFAULT',
validate => TRUE,
replace => TRUE,
force_match => FALSE /* TRUE:FORCE (match even when different literals in SQL). FALSE:EXACT (similar to CURSOR_SHARING) */ );
-- drop sql profile staging table for original sql (if one exists)
BEGIN
DBMS_OUTPUT.PUT_LINE('dropping staging table "STGTAB_SQLPROF_'||UPPER(TRIM('&&original_sql_id.'))||'"');
EXECUTE IMMEDIATE 'DROP TABLE STGTAB_SQLPROF_'||UPPER(TRIM('&&original_sql_id.'));
EXCEPTION
WHEN OTHERS THEN
DBMS_OUTPUT.PUT_LINE('staging table "STGTAB_SQLPROF_'||UPPER(TRIM('&&original_sql_id.'))||'" did not exist');
END;
-- create sql profile staging table for original sql
DBMS_OUTPUT.PUT_LINE('creating staging table "STGTAB_SQLPROF_'||UPPER(TRIM('&&original_sql_id.'))||'"');
DBMS_SQLTUNE.CREATE_STGTAB_SQLPROF (
table_name => 'STGTAB_SQLPROF_'||UPPER(TRIM('&&original_sql_id.')),
schema_name => '&&connected_user.' );
-- packs new sql profile for original sql
DBMS_OUTPUT.PUT_LINE('packaging new sql profile into staging table "STGTAB_SQLPROF_'||UPPER(TRIM('&&original_sql_id.'))||'"');
DBMS_SQLTUNE.PACK_STGTAB_SQLPROF (
profile_name => :name,
staging_table_name => 'STGTAB_SQLPROF_'||UPPER(TRIM('&&original_sql_id.')),
staging_schema_owner => '&&connected_user.' );
END;
/
-- profile_name
COL profile_name NEW_V profile_name FOR A30;
SELECT :name profile_name FROM DUAL;
-- display details of new sql_profile
SET ECHO ON;
REM
REM SQL Profile
REM ~~~~~~~~~~~
REM
SELECT signature, name, category, type, status
FROM dba_sql_profiles WHERE name = :name;
SELECT description
FROM dba_sql_profiles WHERE name = :name;
SET ECHO OFF;
PRO
PRO ****************************************************************************
PRO * Enter &&connected_user. password to export staging table STGTAB_SQLPROF_&&original_sql_id.
PRO ****************************************************************************
HOS exp &&connected_user. tables=&&connected_user..STGTAB_SQLPROF_&&original_sql_id. file=STGTAB_SQLPROF_&&original_sql_id..dmp statistics=NONE indexes=N constraints=N grants=N triggers=N
PRO
PRO If you need to implement this Custom SQL Profile on a similar system,
PRO import and unpack using these commands:
PRO
PRO imp &&connected_user. file=STGTAB_SQLPROF_&&original_sql_id..dmp tables=STGTAB_SQLPROF_&&original_sql_id. ignore=Y
PRO
PRO BEGIN
PRO DBMS_SQLTUNE.UNPACK_STGTAB_SQLPROF (
PRO profile_name => '&&profile_name.',
PRO replace => TRUE,
PRO staging_table_name => 'STGTAB_SQLPROF_&&original_sql_id.',
PRO staging_schema_owner => '&&connected_user.' );;
PRO END;;
PRO /
PRO
SPO OFF;
HOS zip -m coe_load_sql_profile_&&original_sql_id. coe_load_sql_profile_&&original_sql_id..log STGTAB_SQLPROF_&&original_sql_id..dmp coe_load_sql_profile.log
HOS zip -d coe_load_sql_profile_&&original_sql_id. coe_load_sql_profile.log
WHENEVER SQLERROR CONTINUE;
SET DEF ON TERM ON ECHO OFF FEED 6 VER ON HEA ON LIN 80 PAGES 14 LONG 80 LONGC 80 TRIMS OFF TI OFF TIMI OFF SERVEROUT OFF NUM 10 SQLP SQL>;
SET SERVEROUT OFF;
UNDEFINE 1 2 3 original_sql_id modified_sql_id plan_hash_value profile_name
CL COL
PRO
PRO coe_load_sql_profile completed.问题处理结果：
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