[20201231]RAC buffer states: XCUR, SCUR, PI,CR.txt
[20201231]RAC buffer states: XCUR, SCUR, PI,CR.txt
--//别人问及rac buffer状态PI，按照文档介绍就是past image.
■ Note If you have SYS privileges you can run the following query to see how many blocks you have in what
state: select state, count(*) from x$bh group by state; The commonest states are: 0—free, 1—XCUR
(exclusive current), 2—SCUR (shared current), 3—CR (available only for consistent read), 8—PI (past image). This
isn't a nice thing to do to your buffer cache, so resist the temptation to do it on a busy production system with a
large cache.
--//RAC涉及缓存融合以及资源掌控方面的问题，搞的比单实例的数据库要复杂N多。
--//不过我找到一篇blog。http://www.dbi-services.com/index.php/blog/entry/rac-buffer-states-xcur-scur-pi-ci
--//注：后面的ci我估计做者笔误，应该不是CI而是CR。我在本身的环境下重复测试，说明问题。
1.环境：
SYS@192.168.90.18:1521/fyhis/fyhis1> @ 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
$ cat bhy.sql
SELECT inst_id
,class#
,status
,lock_element_addr
,dirty
,temp
,ping
,stale
,direct
,new
FROM gv$bh
WHERE objd = (SELECT data_object_id
FROM dba_objects
WHERE owner = 'SCOTT' AND object_name = 'DEPT')
AND status != 'free'
ORDER BY inst_id;
$ cat bh.sql
set echo off
--------------------------------------------------------------------------------
-- @name: bh
-- @author: dion cho
-- @note: show block header
-- @usage: @bh f# b# state
--------------------------------------------------------------------------------
col object_name format a20
col state format a10
select
b.inst_id,
b.hladdr,
b.dbarfil,
b.dbablk,
b.class,
decode(b.class,1,'data block',2,'sort block',3,'save undo block', 4,
'segment header',5,'save undo header',6,'free list',7,'extent map',
8,'1st level bmb',9,'2nd level bmb',10,'3rd level bmb', 11,'bitmap block',
12,'bitmap index block',13,'file header block',14,'unused',
15,'system undo header',16,'system undo block', 17,'undo header',
18,'undo block') class_type,
decode(state,0,'free',1,'xcur',2,'scur',3,'cr', 4,'read',5,'mrec',6,'irec',7,'write',8,'pi', 9,'memory',10,'mwrite',11,'donated') as state,
b.tch,
cr_scn_bas,
cr_scn_wrp,
cr_uba_fil,
cr_uba_blk,
cr_uba_seq,
ba,
b.LE_ADDR,
(select object_name from dba_objects where data_object_id = b.obj) as object_name
from x$bh b
where
dbarfil = &1 and
dbablk = &2
;
--//增长LE_ADDR，inst_id字段，我发如今单实例上LE_ADDR输出是00.
SYS@192.168.90.18:1521/fyhis/fyhis1> select rowid from scott.dept where deptno=10;
ROWID
------------------
AAAVRCAAEAAAACHAAA
SYS@192.168.90.18:1521/fyhis/fyhis1> @ rowid AAAVRCAAEAAAACHAAA
OBJECT FILE BLOCK ROW ROWID_DBA DBA TEXT
---------- ---------- ---------- ---------- -------------------- -------------------- ----------------------------------------
87106 4 135 0 0x1000087 4,135 alter system dump datafile 4 block 135 ;
SYS@192.168.90.18:1521/fyhis/fyhis1> @ bh 4 135
no rows selected
--//没有输出正常，由于并无访问对应的数据块。
2.测试：
--//session 1:
SYS@192.168.90.18:1521/fyhis/fyhis1> select * from scott.dept where rowid='AAAVRCAAEAAAACHAAA';
DEPTNO DNAME LOC
---------- -------------- -------------
10 ACCOUNTING NEW YORK
SYS@192.168.90.18:1521/fyhis/fyhis1> @ bh 4 135
INST_ID HLADDR DBARFIL DBABLK CLASS CLASS_TYPE STATE TCH CR_SCN_BAS CR_SCN_WRP CR_UBA_FIL CR_UBA_BLK CR_UBA_SEQ BA LE_ADDR OBJECT_NAME
---------- ---------------- ---------- ---------- ---------- ------------------ ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------------- ---------------- --------------------
1 00000004E22F9FD8 4 135 1 data block scur 1 0 0 0 0 0 0000000461890000 0000000117F2B4D8 DEPT
SYS@192.168.90.18:1521/fyhis/fyhis1> @ bhy 4 135
INST_ID CLASS# STATUS LOCK_ELEMENT_ADD D T P S D N
---------- ---------- ---------- ---------------- - - - - - -
1 1 scur 0000000117F2B4D8 N N N N N N
--//仅仅出如今1个数据库实例上。
--//注意state=scur,而不是像单实例出现的是state=xcur.也许这个是RAC的特性.
--//session 2,执行呢？
SYS@192.168.90.18:1521/fyhis/fyhis2> select * from scott.dept where rowid='AAAVRCAAEAAAACHAAA';
DEPTNO DNAME LOC
---------- -------------- -------------
10 ACCOUNTING NEW YORK
SYS@192.168.90.18:1521/fyhis/fyhis2> @ bh 4 135
INST_ID HLADDR DBARFIL DBABLK CLASS CLASS_TYPE STATE TCH CR_SCN_BAS CR_SCN_WRP CR_UBA_FIL CR_UBA_BLK CR_UBA_SEQ BA LE_ADDR OBJECT_NAME
---------- ---------------- ---------- ---------- ---------- ------------------ ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------------- ---------------- --------------------
2 00000004E239D750 4 135 1 data block scur 2 0 0 0 0 0 000000037465A000 0000000223FB8D68 DEPT
SYS@192.168.90.18:1521/fyhis/fyhis2> @ bhy 4 135
INST_ID CLASS# STATUS LOCK_ELEMENT_ADD D T P S D N
---------- ---------- ---------- ---------------- - - - - - -
1 1 scur 0000000117F2B4D8 N N N N N N
2 1 scur 0000000223FB8D68 N N N N N N
--//没有修改块，两边都是共享的。state=scur.
3.继续测试：
--//session 1，作一个修改，注个人测试与原连接不一样，我没有刷新数据缓存：
SYS@192.168.90.18:1521/fyhis/fyhis1> select * from scott.dept where rowid='AAAVRCAAEAAAACHAAA' for update;
DEPTNO DNAME LOC
---------- -------------- -------------
10 ACCOUNTING NEW YORK
SYS@192.168.90.18:1521/fyhis/fyhis1> @ bh 4 135
INST_ID HLADDR DBARFIL DBABLK CLASS CLASS_TYPE STATE TCH CR_SCN_BAS CR_SCN_WRP CR_UBA_FIL CR_UBA_BLK CR_UBA_SEQ BA LE_ADDR OBJECT_NAME
---------- ---------------- ---------- ---------- ---------- ------------------ ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------------- ---------------- --------------------
1 00000004E22F9FD8 4 135 1 data block xcur 2 0 0 0 0 0 00000000A076A000 0000000117F2B4D8 DEPT
1 00000004E22F9FD8 4 135 1 data block cr 2 3703090073 7 0 0 0 0000000461890000 00 DEPT
SYS@192.168.90.18:1521/fyhis/fyhis1> @ bhy
INST_ID CLASS# STATUS LOCK_ELEMENT_ADD D T P S D N
---------- ---------- ---------- ---------------- - - - - - -
1 1 xcur 0000000117F2B4D8 Y N N N N N
1 1 cr 00 N N N N N N
2 1 cr 00 N N N N N N
--//session 2:
SYS@192.168.90.18:1521/fyhis/fyhis2> @ bh 4 135
INST_ID HLADDR DBARFIL DBABLK CLASS CLASS_TYPE STATE TCH CR_SCN_BAS CR_SCN_WRP CR_UBA_FIL CR_UBA_BLK CR_UBA_SEQ BA LE_ADDR OBJECT_NAME
---------- ---------------- ---------- ---------- ---------- ------------------ ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------------- ---------------- --------------------
2 00000004E239D750 4 135 1 data block cr 1 3703090072 7 0 0 0 000000037465A000 00 DEPT
--//看看在两个实例上执行bh.sql脚本的输出。
--//实例2的STATE从scur->CR，而CR_SCN_BAS从0变成了3703090072。
--//实例1的STATE从scur->CR，而CR_SCN_BAS从0变成了3703090073。也就是先要修改实例2的状态在修改实例1的状态们(从scn信息能够看出来)。
--//实例1上生成新块state=xcur.
--//在session 2继续执行：
SYS@192.168.90.18:1521/fyhis/fyhis2> select * from scott.dept where rowid='AAAVRCAAEAAAACHAAA';
DEPTNO DNAME LOC
---------- -------------- -------------
10 ACCOUNTING NEW YORK
SYS@192.168.90.18:1521/fyhis/fyhis2> @ bh 4 135
INST_ID HLADDR DBARFIL DBABLK CLASS CLASS_TYPE STATE TCH CR_SCN_BAS CR_SCN_WRP CR_UBA_FIL CR_UBA_BLK CR_UBA_SEQ BA LE_ADDR OBJECT_NAME
---------- ---------------- ---------- ---------- ---------- ------------------ ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------------- ---------------- --------------------
2 00000004E239D750 4 135 1 data block cr 1 3703090708 7 0 0 0 0000000384620000 00 DEPT
2 00000004E239D750 4 135 1 data block cr 1 3703090072 7 0 0 0 000000037465A000 00 DEPT
--//增长1行,state=cr.
SYS@192.168.90.18:1521/fyhis/fyhis2> @ bhy
INST_ID CLASS# STATUS LOCK_ELEMENT_ADD D T P S D N
---------- ---------- ---------- ---------------- - - - - - -
1 1 xcur 0000000117F2B4D8 Y N N N N N
1 1 cr 00 N N N N N N
1 1 cr 00 N N N N N N
2 1 cr 00 N N N N N N
2 1 cr 00 N N N N N N
--//session 1:
SYS@192.168.90.18:1521/fyhis/fyhis1> @ bh 4 135
INST_ID HLADDR DBARFIL DBABLK CLASS CLASS_TYPE STATE TCH CR_SCN_BAS CR_SCN_WRP CR_UBA_FIL CR_UBA_BLK CR_UBA_SEQ BA LE_ADDR OBJECT_NAME
---------- ---------------- ---------- ---------- ---------- ------------------ ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------------- ---------------- --------------------
1 00000004E22F9FD8 4 135 1 data block cr 0 3703090708 7 3 4278 36326 0000000190F96000 00 DEPT
1 00000004E22F9FD8 4 135 1 data block xcur 2 0 0 0 0 0 00000000A076A000 0000000117F2B4D8 DEPT
1 00000004E22F9FD8 4 135 1 data block cr 2 3703090073 7 0 0 0 0000000461890000 00 DEPT
--//你能够发现如今实例1上构造出CR_SCN_BAS=3703090708,而后在传输到实例2上。
--//session 2,注意修改发生在实例1:
SYS@192.168.90.18:1521/fyhis/fyhis2> alter system checkpoint;
System altered.
SYS@192.168.90.18:1521/fyhis/fyhis2> @ bhy
INST_ID CLASS# STATUS LOCK_ELEMENT_ADD D T P S D N
---------- ---------- ---------- ---------------- - - - - - -
1 1 xcur 0000000117F2B4D8 N N N N N N
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 1 cr 00 N N N N N N
1 1 cr 00 N N N N N N
2 1 cr 00 N N N N N N
2 1 cr 00 N N N N N N
--//dirty标识清除。发生在实例1.
4.测试STATE=PI的状态如何出现：
--//session 1:
SYS@192.168.90.18:1521/fyhis/fyhis1> commit ;
Commit complete.
SYS@192.168.90.18:1521/fyhis/fyhis1> alter system checkpoint;
System altered.
SYS@192.168.90.18:1521/fyhis/fyhis1> @ bhy
INST_ID CLASS# STATUS LOCK_ELEMENT_ADD D T P S D N
---------- ---------- ---------- ---------------- - - - - - -
1 1 xcur 0000000117F2B4D8 Y N N N N N
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 1 cr 00 N N N N N N
1 1 cr 00 N N N N N N
2 1 cr 00 N N N N N N
2 1 cr 00 N N N N N N
--//变成了脏块.
--//session 2:
SYS@192.168.90.18:1521/fyhis/fyhis2> select * from scott.dept where rowid='AAAVRCAAEAAAACHAAA' for update;
DEPTNO DNAME LOC
---------- -------------- -------------
10 ACCOUNTING NEW YORK
SYS@192.168.90.18:1521/fyhis/fyhis2> @ bhy
INST_ID CLASS# STATUS LOCK_ELEMENT_ADD D T P S D N
---------- ---------- ---------- ---------------- - - - - - -
1 1 cr 00 N N N N N N
1 1 cr 00 N N N N N N
1 1 pi 0000000117F2B4D8 Y N N N N N
2 1 cr 00 N N N N N N
2 1 cr 00 N N N N N N
2 1 cr 00 N N N N N N
2 1 xcur 0000000223FB8D68 Y N N N N N
7 rows selected.
--//注意看dirty标识，两个依旧标识为Y。实例1原来的state 从xcur->pi,也就是post image.
SYS@192.168.90.18:1521/fyhis/fyhis2> @ bh 4 135
INST_ID HLADDR DBARFIL DBABLK CLASS CLASS_TYPE STATE TCH CR_SCN_BAS CR_SCN_WRP CR_UBA_FIL CR_UBA_BLK CR_UBA_SEQ BA LE_ADDR OBJECT_NAME
---------- ---------------- ---------- ---------- ---------- ------------------ ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------------- ---------------- --------------------
2 00000004E239D750 4 135 1 data block xcur 1 0 0 0 0 0 00000003C8108000 0000000223FB8D68 DEPT
2 00000004E239D750 4 135 1 data block cr 1 3703092337 7 0 0 0 00000003B5A72000 00 DEPT
2 00000004E239D750 4 135 1 data block cr 1 3703090708 7 0 0 0 0000000384620000 00 DEPT
2 00000004E239D750 4 135 1 data block cr 1 3703090072 7 0 0 0 000000037465A000 00 DEPT
--//session 1查看:
SYS@192.168.90.18:1521/fyhis/fyhis1> @ bh 4 135
INST_ID HLADDR DBARFIL DBABLK CLASS CLASS_TYPE STATE TCH CR_SCN_BAS CR_SCN_WRP CR_UBA_FIL CR_UBA_BLK CR_UBA_SEQ BA LE_ADDR OBJECT_NAME
---------- ---------------- ---------- ---------- ---------- ------------------ ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------------- ---------------- --------------------
1 00000004E22F9FD8 4 135 1 data block cr 0 3703090708 7 3 4278 36326 0000000190F96000 00 DEPT
1 00000004E22F9FD8 4 135 1 data block pi 2 0 0 0 0 0 00000000A076A000 0000000117F2B4D8 DEPT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 00000004E22F9FD8 4 135 1 data block cr 2 3703090073 7 0 0 0 0000000461890000 00 DEPT
--//实例1的原来state=xcur 变成了 state = pi.
--//session 2:
SYS@192.168.90.18:1521/fyhis/fyhis2> alter system checkpoint;
System altered.
SYS@192.168.90.18:1521/fyhis/fyhis2> @ bhy
INST_ID CLASS# STATUS LOCK_ELEMENT_ADD D T P S D N
---------- ---------- ---------- ---------------- - - - - - -
1 1 cr 00 N N N N N N
1 1 cr 00 N N N N N N
1 1 cr 00 N N N N N N
2 1 cr 00 N N N N N N
2 1 cr 00 N N N N N N
2 1 cr 00 N N N N N N
2 1 xcur 0000000223FB8D68 N N N N N N
7 rows selected.
--//state=pi标识清除，变成了cr，并且lock_element_addr=00.而且标识dirty变成Y->N(2个实例)
--//session 1:
SYS@192.168.90.18:1521/fyhis/fyhis1> @ bh 4 135
INST_ID HLADDR DBARFIL DBABLK CLASS CLASS_TYPE STATE TCH CR_SCN_BAS CR_SCN_WRP CR_UBA_FIL CR_UBA_BLK CR_UBA_SEQ BA LE_ADDR OBJECT_NAME
---------- ---------------- ---------- ---------- ---------- ------------------ ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------------- ---------------- --------------------
1 00000004E22F9FD8 4 135 1 data block cr 0 3703090708 7 3 4278 36326 0000000190F96000 00 DEPT
1 00000004E22F9FD8 4 135 1 data block cr 1 3703092337 7 0 0 0 00000000A076A000 00 DEPT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 00000004E22F9FD8 4 135 1 data block cr 2 3703090073 7 0 0 0 0000000461890000 00 DEPT
--//特别注意下划线的CR_SCN_BAS=3703092337.原来是0. 很奇怪的是TCH从2变成了1,LE_ADDR=00.
--//session 2:
SYS@192.168.90.18:1521/fyhis/fyhis2> @ bh 4 135
INST_ID HLADDR DBARFIL DBABLK CLASS CLASS_TYPE STATE TCH CR_SCN_BAS CR_SCN_WRP CR_UBA_FIL CR_UBA_BLK CR_UBA_SEQ BA LE_ADDR OBJECT_NAME
---------- ---------------- ---------- ---------- ---------- ------------------ ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------------- ---------------- --------------------
2 00000004E239D750 4 135 1 data block xcur 1 0 0 0 0 0 00000003C8108000 0000000223FB8D68 DEPT
2 00000004E239D750 4 135 1 data block cr 1 3703092337 7 0 0 0 00000003B5A72000 00 DEPT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2 00000004E239D750 4 135 1 data block cr 1 3703090708 7 0 0 0 0000000384620000 00 DEPT
2 00000004E239D750 4 135 1 data block cr 1 3703090072 7 0 0 0 000000037465A000 00 DEPT
--//注意看下划线以及CR_SCN_BAS列的变化。你能够猜想大概操做流程，先从实例1传输或者拷贝过来，而后在修改。
--//从实例1 CR_SCN_BAS=0 变成 3703092337，就能够看出来。
5.继续测试：
--//从实例2读取特定scn的状况。
--//7,3703090073 = scn(10): 33767861145 = scn(16): 0x7dcb8ab99
--//session 2:
SYS@192.168.90.18:1521/fyhis/fyhis2> commit ;
Commit complete.
SYS@192.168.90.18:1521/fyhis/fyhis2> select * from scott.dept as of scn 33767861145 where rowid='AAAVRCAAEAAAACHAAA' ;
DEPTNO DNAME LOC
---------- -------------- -------------
10 ACCOUNTING NEW YORK
SYS@192.168.90.18:1521/fyhis/fyhis2> @ bh 4 135
INST_ID HLADDR DBARFIL DBABLK CLASS CLASS_TYPE STATE TCH CR_SCN_BAS CR_SCN_WRP CR_UBA_FIL CR_UBA_BLK CR_UBA_SEQ BA LE_ADDR OBJECT_NAME
---------- ---------------- ---------- ---------- ---------- ------------------ ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------------- ---------------- --------------------
2 00000004E239D750 4 135 1 data block xcur 1 0 0 0 0 0 00000003C8108000 0000000223FB8D68 DEPT
2 00000004E239D750 4 135 1 data block cr 1 3703092337 7 0 0 0 00000003B5A72000 00 DEPT
2 00000004E239D750 4 135 1 data block cr 2 3703090708 7 0 0 0 0000000384620000 00 DEPT
2 00000004E239D750 4 135 1 data block cr 1 3703090072 7 0 0 0 000000037465A000 00 DEPT
--//session 1:
SYS@192.168.90.18:1521/fyhis/fyhis1> @ bh 4 135
INST_ID HLADDR DBARFIL DBABLK CLASS CLASS_TYPE STATE TCH CR_SCN_BAS CR_SCN_WRP CR_UBA_FIL CR_UBA_BLK CR_UBA_SEQ BA LE_ADDR OBJECT_NAME
---------- ---------------- ---------- ---------- ---------- ------------------ ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------------- ---------------- --------------------
1 00000004E22F9FD8 4 135 1 data block cr 0 3703090708 7 3 4278 36326 0000000190F96000 00 DEPT
1 00000004E22F9FD8 4 135 1 data block cr 1 3703092337 7 0 0 0 00000000A076A000 00 DEPT
1 00000004E22F9FD8 4 135 1 data block cr 2 3703090073 7 0 0 0 0000000461890000 00 DEPT
--//没有变化，甚至tch值。视乎这样的查询仅仅经过实例1传输过来。
--//session 1,重复上面的查询：
SYS@192.168.90.18:1521/fyhis/fyhis1> select * from scott.dept as of scn 33767861145 where rowid='AAAVRCAAEAAAACHAAA' ;
DEPTNO DNAME LOC
---------- -------------- -------------
10 ACCOUNTING NEW YORK
SYS@192.168.90.18:1521/fyhis/fyhis1> @ bh 4 135
INST_ID HLADDR DBARFIL DBABLK CLASS CLASS_TYPE STATE TCH CR_SCN_BAS CR_SCN_WRP CR_UBA_FIL CR_UBA_BLK CR_UBA_SEQ BA LE_ADDR OBJECT_NAME
---------- ---------------- ---------- ---------- ---------- ------------------ ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------------- ---------------- --------------------
1 00000004E22F9FD8 4 135 1 data block cr 0 3703090708 7 3 4278 36326 0000000190F96000 00 DEPT
1 00000004E22F9FD8 4 135 1 data block cr 1 3703092337 7 0 0 0 00000000A076A000 00 DEPT
1 00000004E22F9FD8 4 135 1 data block cr 3 3703090073 7 0 0 0 0000000461890000 00 DEPT
--//能够发现TCH从2 -> 3.
--//session 2,改变scn看看呢？
SYS@192.168.90.18:1521/fyhis/fyhis2> select * from scott.dept as of scn 33767861146 where rowid='AAAVRCAAEAAAACHAAA' ;
DEPTNO DNAME LOC
---------- -------------- -------------
10 ACCOUNTING NEW YORK
--//33767861146 = scn_wrap,scn_base(10): 7,3703090074 = scn_wrap,scn_base(16): 0x7,0xdcb8ab9a
SYS@192.168.90.18:1521/fyhis/fyhis2> @ bh 4 135
INST_ID HLADDR DBARFIL DBABLK CLASS CLASS_TYPE STATE TCH CR_SCN_BAS CR_SCN_WRP CR_UBA_FIL CR_UBA_BLK CR_UBA_SEQ BA LE_ADDR OBJECT_NAME
---------- ---------------- ---------- ---------- ---------- ------------------ ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------------- ---------------- --------------------
2 00000004E239D750 4 135 1 data block xcur 1 0 0 0 0 0 00000003C8108000 0000000223FB8D68 DEPT
2 00000004E239D750 4 135 1 data block cr 1 3703092337 7 0 0 0 00000003B5A72000 00 DEPT
2 00000004E239D750 4 135 1 data block cr 3 3703090708 7 0 0 0 0000000384620000 00 DEPT
2 00000004E239D750 4 135 1 data block cr 1 3703090072 7 0 0 0 000000037465A000 00 DEPT
--//若是你仔细观察就能发现CR_SCN_BAS=3703090708的TCH从2->3.也就是构造从当前实例CR_SCN_BAS=3703090708 反向操做会 scn= 7,3703090074.
--//session 1:
SYS@192.168.90.18:1521/fyhis/fyhis1> @ bh 4 135
INST_ID HLADDR DBARFIL DBABLK CLASS CLASS_TYPE STATE TCH CR_SCN_BAS CR_SCN_WRP CR_UBA_FIL CR_UBA_BLK CR_UBA_SEQ BA LE_ADDR OBJECT_NAME
---------- ---------------- ---------- ---------- ---------- ------------------ ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------------- ---------------- --------------------
1 00000004E22F9FD8 4 135 1 data block cr 0 3703090708 7 3 4278 36326 0000000190F96000 00 DEPT
1 00000004E22F9FD8 4 135 1 data block cr 1 3703092337 7 0 0 0 00000000A076A000 00 DEPT
1 00000004E22F9FD8 4 135 1 data block cr 3 3703090073 7 0 0 0 0000000461890000 00 DEPT
6.总结：
--//至于为何出现PI，按照文档介绍节省recovery的恢复时间,一些细节操做个人分析能力。
--//测试仍是有点乱....
--//http://www.dbi-services.com/index.php/blog/entry/rac-buffer-states-xcur-scur-pi-ci
Here are the states we have seen here:
XCUR: current version of the block - holding an exclusive lock for it
SCUR: current version of the block that can be share because no modification were done
CR: only valid for consistent read, after applying the necessary undo to get it back to requried SCN
PI: past image of a modified current block, kept until the latest version is checkpointed
and the other possible states:
FREE: The buffer is not currently in use.
READ: when the block is being read from disk
MREC: when the block is being recovered for media recovery
IREC: when the block is being recovered for crash recovery
--//实际上rac并不是是什么好东西,处理很差比单实例要慢,特别是原来单实例就存在性能问题的状况下,rac环境可能放大这样的效果.
--//并且从上面测试也能够看出几点:
--//1.事务应该仍是尽量的快速提交.
--//2.内联的网络传输能力要尽可能的块.尽量进行业务分割.相同的业务在1个实例处理.我还见过内联网络使用hub的状况.
--// 这种网络设备通常就是100M,全双工也就是200M,最大传输能力就是20M/秒.这样若是内联流量很大,出现问题的可能性很大.
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