[20160104]enq RC-Result Cache Contention

[20160104]enq RC - Result Cache Contention.txt

--今天检查awr报表，无意间发现enq RC - Result Cache Contention排在靠前的位置。我们服务器很强劲，出现这个给仔细检查。

1.环境：
[email protected]:1521/XXXX> @ &r/ver1
PORT_STRING                    VERSION        BANNER
------------------------------ -------------- --------------------------------------------------------------------------------
x86_64/Linux 2.4.xx            11.2.0.4.0     Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production

2.分析：
SELECT sql_id, COUNT (*)
    FROM DBA_HIST_ACTIVE_SESS_HISTORY
   WHERE event = 'enq: RC - Result Cache: Contention'
GROUP BY sql_id;

SQL_ID          COUNT(*)
------------- ----------
5wh51638vh3jc          1
futfjyqv0c6b8         28

--很明显问题集中在sql_id='futfjyqv0c6b8'.

[email protected]:1521/XXXX> @ &r/sqlid futfjyqv0c6b8
SQL_ID        SQLTEXT
------------- --------------------------------------------------------------------------------------------------------------------------------------------------------
futfjyqv0c6b8 select emr_zlsqmx.mxid,emr_zlsqmx.sqdh,emr_zlsqmx.zlxmid,emr_zlsqmx.xmmc,emr_zlsqmx.xmlb,emr_zlsqmx.sypc,emr_zlsqmx.sysl,emr_zlsqmx.plsx,emr_zlsqmx.ysy
              zbh,emr_zlsqmx.yszt  from emr_zlsqmx

--可以发现很简单访问就是表emr_zlsqmx。而且这张表是我节前修改result cache模式的。

[email protected]:1521/XXXX> select segment_name,SEGMENT_TYPE,SEGMENT_SUBTYPE,BYTES,BLOCKS,EXTENTS from dba_segments where segment_name='EMR_ZLSQMX';
SEGMENT_NAME         SEGMENT_TYPE       SEGMENT_SU      BYTES     BLOCKS    EXTENTS
-------------------- ------------------ ---------- ---------- ---------- ----------
EMR_ZLSQMX           TABLE              ASSM         17825792       2176         32

--大小17825792/1024/1024=17M。

[email protected]:1521/XXXX> @ &r/ddl BBBBBB_BBB.EMR_ZLSQMX
C100
------------------------------------------------------------------------------
  CREATE TABLE "BBBBBB_BBB"."EMR_ZLSQMX"
   (    "MXID" NUMBER(18,0) NOT NULL ENABLE,
        "SQDH" NUMBER(18,0) NOT NULL ENABLE,
        "ZLXMID" NUMBER(8,0) NOT NULL ENABLE,
        "XMMC" VARCHAR2(255) NOT NULL ENABLE,
        "XMLB" NUMBER(1,0) NOT NULL ENABLE,
        "SYPC" VARCHAR2(6),
        "SYSL" NUMBER(5,2),
        "PLSX" NUMBER(3,0),
        "YSYZBH" NUMBER(18,0),
        "YSZT" VARCHAR2(120),
         CONSTRAINT "PK_EMR_ZLSQMX" PRIMARY KEY ("MXID")
  USING INDEX PCTFREE 10 INITRANS 2 MAXTRANS 255 COMPUTE STATISTICS
  STORAGE(INITIAL 196608 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645
  PCTINCREASE 0 FREELISTS 1 FREELIST GROUPS 1
  BUFFER_POOL DEFAULT FLASH_CACHE DEFAULT CELL_FLASH_CACHE DEFAULT)
  TABLESPACE "BBBBBB_BBB"  ENABLE,
         SUPPLEMENTAL LOG GROUP "GGS_87299" ("MXID") ALWAYS
   ) SEGMENT CREATION IMMEDIATE
  PCTFREE 10 PCTUSED 40 INITRANS 1 MAXTRANS 255
NOCOMPRESS LOGGING
  STORAGE(INITIAL 589824 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645
  PCTINCREASE 0 FREELISTS 1 FREELIST GROUPS 1
  BUFFER_POOL DEFAULT FLASH_CACHE DEFAULT CELL_FLASH_CACHE DEFAULT)
  TABLESPACE "BBBBBB_BBB"
  RESULT_CACHE(MODE FORCE) ;

[email protected]:1521/XXXX> select * from DBA_TAB_MODIFICATIONS where table_name='EMR_ZLSQMX';
TABLE_OWNER  TABLE_NAME SUBPARTITION_NAME  INSERTS    UPDATES    DELETES TIMESTAMP           TRU DROP_SEGMENTS
------------ ---------- ------------------ ------- ---------- ---------- ------------------- --- -------------
BBBBBB_BBB   EMR_ZLSQMX                       4730        148         13 2016-01-03 17:11:45 NO              0

--奇怪这个是应用的字典表，估计这段时间用户在维护这张表吗？

SELECT sql_id,count(*)
  FROM V$ACTIVE_SESSION_HISTORY
WHERE event = 'enq: RC - Result Cache: Contention'
group by sql_id

SQL_ID          COUNT(*)
------------- ----------
g7ytdh9mxt1s0          2
futfjyqv0c6b8         46

--会不会显示这个的结果集太大，导致的问题。我在sqlplus设置
set autot traceonly
set timing on
--大约执行10次会出现1次存在consistent gets的情况。

[email protected]:1521/XXXX> select * from DBA_TAB_MODIFICATIONS where table_name='EMR_ZLSQMX';

TABLE_OWNER  TABLE_NAME PARTITION_NAME  SUBPARTITION_NAME     INSERTS    UPDATES    DELETES TIMESTAMP           TRU DROP_SEGMENTS
------------ ---------- --------------- ------------------ ---------- ---------- ---------- ------------------- --- -------------
BBBBBB_BBB   EMR_ZLSQMX                                          4730        148         13 2016-01-03 17:11:45 NO              0

[email protected]:1521/XXXX> exec sys.DBMS_STATS.FLUSH_DATABASE_MONITORING_INFO()
PL/SQL procedure successfully completed.

[email protected]:1521/XXXX> select * from DBA_TAB_MODIFICATIONS where table_name='EMR_ZLSQMX';
TABLE_OWNER  TABLE_NAME PARTITION_NAME  SUBPARTITION_NAME     INSERTS    UPDATES    DELETES TIMESTAMP           TRU DROP_SEGMENTS
------------ ---------- --------------- ------------------ ---------- ---------- ---------- ------------------- --- -------------
BBBBBB_BBB   EMR_ZLSQMX                                          6298        197         15 2016-01-04 15:27:28 NO              0

--很明显这个表存在"大量"的DML操作。

[email protected]:1521/XXXX> SELECT id,TYPE,status,NAME,object_no,cache_id,invalidations,scn FROM v$result_cache_objects where INVALIDATIONS>=1000;
        ID TYPE         STATUS    NAME                   OBJECT_NO CACHE_ID               INVALIDATIONS           SCN
---------- ------------ --------- --------------------- ---------- ---------------------- ------------- -------------
    129667 Dependency   Published BBBBBB_BBB.EMR_ZLSQMX      93765 BBBBBB_BBB.EMR_ZLSQMX           3817   14406729743
    336708 Dependency   Published BBBBBB_BBB.YF_DB01         96396 BBBBBB_BBB.YF_DB01             25145   14406725573
     39171 Dependency   Published BBBBBB_BBB.GY_XTCS         94089 BBBBBB_BBB.GY_XTCS            397620   14406731157
     39283 Dependency   Published BBBBBB_BBB.GY_YHCS         94111 BBBBBB_BBB.GY_YHCS            660917   14406730951
         3 Dependency   Published BBBBBB_BBB.GY_YGDM         94105 BBBBBB_BBB.GY_YGDM              5378   14406354949

--这条语句本来不存在优化的可能性。而且查询有关Result Cache的等待事件都是围绕这条语句。先取消RESULT_CACHE的设置。

[email protected]:1521/XXXX> ALTER TABLE BBBBBB_BBB.EMR_ZLSQMX RESULT_CACHE (MODE DEFAULT);
Table altered.

--昏，仔细检查这个表不是应用的字典表，叫"治疗申请单_单据分类明细项目",没有谓词条件，这样不是越查越慢吗？对于这样的开发真
--的很无语。

[email protected]:1521/XXXX> select * from DBA_TAB_MODIFICATIONS where table_name='EMR_ZLSQMX';

TABLE_OWNER  TABLE_NAME PARTITION_NAME  SUBPARTITION_NAME     INSERTS    UPDATES    DELETES TIMESTAMP           TRU DROP_SEGMENTS
------------ ---------- --------------- ------------------ ---------- ---------- ---------- ------------------- --- -------------
BBBBBB_BBB   EMR_ZLSQMX                                          6298        197         15 2016-01-04 15:27:28 NO              0

[email protected]:1521/XXXX> exec sys.DBMS_STATS.FLUSH_DATABASE_MONITORING_INFO()

PL/SQL procedure successfully completed.

[email protected]:1521/XXXX> select * from DBA_TAB_MODIFICATIONS where table_name='EMR_ZLSQMX';
TABLE_OWNER  TABLE_NAME PARTITION_NAME  SUBPARTITION_NAME     INSERTS    UPDATES    DELETES TIMESTAMP           TRU DROP_SEGMENTS
------------ ---------- --------------- ------------------ ---------- ---------- ---------- ------------------- --- -------------
BBBBBB_BBB   EMR_ZLSQMX                                          6317        198         15 2016-01-04 15:35:11 NO              0

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