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！
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 [email protected] 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：
总结：类似的oracle sql执行计划变化，我处理过多次，他们有相同的业务的特点，就是dml频繁变更业务表中的数据，像本次处理的案例，一次下发要变更近30万次。