latch: cache buffers chains-热块的简单模拟实验

1.创建测试数据.

create table t1 as select rownum id from dba_objects;
CREATE INDEX T1_IDX ON T1(ID) ;

2.创建两个存储过程.

create or replace
PROCEDURE pselect2
AS
l_num number;
BEGIN
FOR i IN 1..1000000
LOOP
SELECT count(*) into l_num FROM T1 where t1.id between 20000 and 30000;
END LOOP;
END;

create or replace
procedure pupdate2
AS
BEGIN
FOR i IN 1..1000000
LOOP
UPDATE t1 SET id = rownum where t1.id  between 20000 and 30000;
COMMIT;
END LOOP;
END;

3.简单模拟几个并发

session 1:exec pselect2;

session 2:exec pselect2;

session 3:exec pselect2;

session 4:exec pupdate2;

session 5:exec pupdate2;

session 6:exec pupdate2;

...

4.查询等待事件

SELECT EVENT,
P1,
P1RAW,
P2,
P2RAW,
state
FROM v$session_wait
WHERE sid IN
(SELECT SID FROM V$SESSION WHERE USERNAME='KIN'
);

EVENT                                       P1 P1RAW                    P2 P2RAW               STATE
------------------------------ ---------- ---------------- ---------- ---------------- --------------------
latch: cache buffers chains    8468531136 00000001F8C387C0          150 0000000000000096 WAITED SHORT TIME
latch: cache buffers chains    8066496552 00000001E0CCF828          150 0000000000000096 WAITED SHORT TIME
latch: cache buffers chains    8064062352 00000001E0A7D390          150 0000000000000096 WAITED SHORT TIME
SQL*Net message from client    1413697536 0000000054435000            1 0000000000000001 WAITING
latch: cache buffers chains    8467468736 00000001F8B351C0          150 0000000000000096 WAITED SHORT TIME
latch: cache buffers chains    8468531136 00000001F8C387C0          150 0000000000000096 WAITED SHORT TIME
latch: cache buffers chains    8064654952 00000001E0B0DE68          150 0000000000000096 WAITED SHORT TIME

5.查询等待事件参数定义

SELECT name,
PARAMETER1,
PARAMETER2,
PARAMETER3
FROM V$EVENT_NAME
WHERE name='latch: cache buffers chains';
NAME                               PARAMETER1                      PARAMETER2                     PARAMETER3
------------------------------ ------------------------------ ------------------------------ ------------------------------
latch: cache buffers chains    address                              number                             tries

5.查询对应热块

SELECT
/*+ RULE */
E.OWNER
|| '.'
|| E.SEGMENT_NAME SEGMENT_NAME,
E.PARTITION_NAME,
E.EXTENT_ID EXTENT#,
X.DBABLK - E.BLOCK_ID + 1 BLOCK#,
X.TCH,
L.CHILD#
FROM SYS.V$LATCH_CHILDREN L,
SYS.X$BH X,
SYS.DBA_EXTENTS E
WHERE X.HLADDR='00000001F8C387C0'
AND E.FILE_ID = X.FILE#
AND X.HLADDR  = L.ADDR
AND X.DBABLK BETWEEN E.BLOCK_ID AND E.BLOCK_ID + E.BLOCKS - 1
ORDER BY X.TCH DESC;

SEGMENT_NAME                       PARTITION_NAME                         EXTENT#     BLOCK#           TCH           CHILD#
------------------------------ ------------------------------ ---------- ---------- ---------- ----------
SYS.I_OBJ4                                                              17         67             1            30264
SYS.WRH$_SYSMETRIC_HISTORY_INDEX                  20        117             1            30264
KIN.T1_IDX                                                               7          2             0            30264
KIN.T1_IDX                                                               7          2            93            30264
KIN.T1_IDX                                                               7          2             1            30264
KIN.T1_IDX                                                               7          2             1            30264
KIN.T1_IDX                                                               7          2             1            30264
KIN.T1_IDX                                                               7          2             1            30264
KIN.T1_IDX                                                               7          2             1            30264

9 rows selected.

至此模拟出索引热块场景.