[20211108]索引分裂块清除日志增加(唯一索引)2.txt
--//链接http://blog.itpub.net/267265/viewspace-2840853/ 测试了索引分裂时遇到的奇怪现象。
--//看看唯一索引发生分裂时发生的情况,上个星期的测试唯一索引时插入最大值，出现10－90分裂，没有设计好，应该选择50－50分裂
--//的情况。
1.环境:
SCOTT@book> @ 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.首先确定索引分裂发生的位置：
SCOTT@book> create table t1 (id number,vc varchar2(100));
Table created.
SCOTT@book> create unique index i_t1_id on t1(id);
Index created.
SCOTT@book> insert into t1 select rownum,rpad(rownum,100,'x') from dual connect by level<=1e3;
1000 rows created.
SCOTT@book> commit ;
Commit complete.
--//分析略。注意不要遗漏这步，避免查询取样问题的影响。
$ cat treedump.sql
column object_id new_value m_index_id
select object_id from user_objects where object_name = upper('&&1') and object_type = 'INDEX';
alter session set events 'immediate trace name treedump level &m_index_id';
SCOTT@book> @ treedump.sql i_t1_id
OBJECT_ID
----------
329453
Session altered.
--//查看转储文件：
branch: 0x10002b3 16777907 (0: nrow: 2, level: 1)
leaf: 0x10002b6 16777910 (-1: nrow: 578 rrow: 578)
leaf: 0x10002b7 16777911 (0: nrow: 422 rrow: 422)
----- end tree dump
--//可以发现唯一索引每块插入的记录更多，这是因为唯一索引rowid部分(不包括data_object_id信息)6字节在键值前面，没有长度指示
--//器,这样每条记录节约1个字节，能容纳更多键值。可以看出插入id=579时出现分裂。
3.开始测试：
--//truncate table t1;
SCOTT@book> insert into t1 select rownum,rpad(rownum,100,'x') from dual connect by level<=577;
577 rows created.
SCOTT@book> commit;
Commit complete.
SCOTT@book> insert into t1 select 579,rpad(579,100,'y') from dual ;
1 row created.
SCOTT@book> commit ;
Commit complete.
SCOTT@book> @ tix
New tracefile_identifier = /u01/app/oracle/diag/rdbms/book/book/trace/book_ora_24971_0001.trc
SCOTT@book> @ treedump.sql i_t1_id
OBJECT_ID
----------
329453
Session altered.
--//查看转储文件：
----- begin tree dump
leaf: 0x10002b3 16777907 (0: nrow: 578 rrow: 578)
----- end tree dump
--//注意不要提交,注意插入不是最大值，不会出现10-90分裂。
SCOTT@book> insert into t1 select 578,rpad(578,100,'z') from dual ;
1 row created.
--//注意不要提交。
SCOTT@book> select rowid,id from t1 where id in (1,578,579);
ROWID ID
------------------ ----------
AABQdBAAEAAAAIkAAA 1
AABQdBAAEAAAAK8AAy 578
AABQdBAAEAAAAK8AAx 579
--//可以看出id =1与后面插入的id=579,578记录在不同一块中,id=578,589在同一块中。
SCOTT@book> @ tix
New tracefile_identifier = /u01/app/oracle/diag/rdbms/book/book/trace/book_ora_24971_0002.trc
SCOTT@book> @ treedump.sql i_t1_id
OBJECT_ID
----------
329453
Session altered.
--//查看转储文件：
----- begin tree dump
branch: 0x10002b3 16777907 (0: nrow: 2, level: 1)
leaf: 0x10002b7 16777911 (-1: nrow: 298 rrow: 298)
leaf: 0x10002b4 16777908 (0: nrow: 281 rrow: 281)
----- end tree dump
--//可以发现发生了索引块分裂50-50，一块占298条(键值id=1-298)，另外一块281条，也就是id=578插入发生在dba=0x10002b4块中。
--//打开新的会话session 1：
SCOTT@book> @ spid
SID SERIAL# PROCESS SERVER SPID PID P_SERIAL# C50
---------- ---------- ------------------------ --------- ------ ------- ---------- --------------------------------------------------
58 5409 24915 DEDICATED 24916 28 174 alter system kill session '58,5409' immediate;
--//记下sid=58.
$ cat viewsessx.sql
column name format a70
SELECT b.NAME, a.statistic#, a.VALUE,a.sid
FROM v$sesstat a, v$statname b
WHERE lower(b.NAME) like lower('%&1%') AND a.statistic# = b.statistic# and a.sid='&&2'
and a.value>0;
SCOTT@book> @ viewsessx 'redo size' 58
NAME STATISTIC# VALUE SID
------------------------------ ---------- ---------- ----------
redo size 194 724 58
SCOTT@book> select * from t1 where id=579;
ID VC
---------- ----------------------------------------------------------------------------------------------------
579 579yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy
SCOTT@book> @ viewsessx 'redo size' 58
NAME STATISTIC# VALUE SID
------------------------------ ---------- ---------- ----------
redo size 194 724 58
--//日志没有增加。唯一索引的好处。
--//测试全表扫描呢？
SCOTT@book> @ viewsessx 'redo size' 58
NAME STATISTIC# VALUE SID
------------------------------ ---------- ---------- ----------
redo size 194 724 58
SCOTT@book> select /*+ full(t1) */ * from t1 where id=579;
ID VC
---------- ----------------------------------------------------------------------------------------------------
579 579yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy
SCOTT@book> @ viewsessx 'redo size' 58
NAME STATISTIC# VALUE SID
------------------------------ ---------- ---------- ----------
redo size 194 832 58
SCOTT@book> select /*+ full(t1) */ * from t1 where id=579;
ID VC
---------- ----------------------------------------------------------------------------------------------------
579 579yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy
SCOTT@book> @ viewsessx 'redo size' 58
NAME STATISTIC# VALUE SID
------------------------------ ---------- ---------- ----------
redo size 194 940 58
--//可以发现全表扫描会出现日志增加的情况。
SCOTT@book> @ viewsessx 'redo size' 58
NAME STATISTIC# VALUE SID
------------------------------ ---------- ---------- ----------
redo size 194 940 58
SCOTT@book> select * from t1 where id=578;
no rows selected
--//看不见正常，因为没有提交。
SCOTT@book> @ viewsessx 'redo size' 58
NAME STATISTIC# VALUE SID
------------------------------ ---------- ---------- ----------
redo size 194 1048 58
--//日志增加，876-768 = 108.
SCOTT@book> @ viewsessx 'redo size' 58
NAME STATISTIC# VALUE SID
------------------------------ ---------- ---------- ----------
redo size 194 1048 58
SCOTT@book> select rowid from t1 where id=578;
no rows selected
SCOTT@book> @ viewsessx 'redo size' 58
NAME STATISTIC# VALUE SID
------------------------------ ---------- ---------- ----------
redo size 194 1156 58
--//日志增加。
SCOTT@book> @ viewsessx 'redo size' 58
NAME STATISTIC# VALUE SID
------------------------------ ---------- ---------- ----------
redo size 194 1156 58
SCOTT@book> select /*+ full(t1) */ * from t1 where id=578;
no rows selected
SCOTT@book> @ viewsessx 'redo size' 58
NAME STATISTIC# VALUE SID
------------------------------ ---------- ---------- ----------
redo size 194 1264 58
--//日志增加。
SCOTT@book> select /*+ full(t1) */ * from t1 where id=678;
no rows selected
SCOTT@book> @ viewsessx 'redo size' 58
NAME STATISTIC# VALUE SID
------------------------------ ---------- ---------- ----------
redo size 194 1372 58
--//日志增加。
--//测试这里基本情况与前面唯一索引看到的情况一致。
--//唯一索引带来一点点好处就是查询select * from t1 where id=:N; N=1-577,579 不会产生日志.
--//而全表扫描select /*+ full(t1) */ * from t1 where id=N1 ;会产生日志
--// 当执行select * from t1 where id=578时 (该记录未提交)，一定会产生日志，在唯一索引我给出解析。
--//仔细想一下当执行select * from t1 where id=578时，首先定位索引块，通过undo重构索引块没有查询到id=578的记录，不用回表。
--//而全表扫描涉及全部数据块，会触摸为提交的脏块，会产生日志。
--//而唯一索引的情况非常特殊select * from t1 where id=:N; N=1-577,579 不会产生日志。
--//问题的源头还是在于，oracle在扫描数据块或者索引段如何知道索引块发生了分裂,为什么一些特殊情况下touch 对应数据块以及索
--//引块时要发生一次Block cleanout record，这样设计的道理何在，那位给出合理的解析。
4.看看日志转储内容。
--//这步不做了，情况与前面类似，就是产生Block cleanout record日志。
5.想起以前的测试：
--//链接 http://blog.itpub.net/267265/viewspace-2775396/=>[20210604]索引分裂与 itl ktbitflg.txt
--//转抄 英文版PDF文档内容 P41:
Table 3-2. Columns in the Interested Transaction List
-----------------------------------------------------------------------------------------------------
Column Description
-----------------------------------------------------------------------------------------------------
...
Flag Bit flag identifying the apparent state of this transaction:
----: active (or "never existed" if every field in the Xid is zero).
--U-: Upper bound commit (also set during "fast commit").
C---: Committed and cleaned out (all associated lock bytes have been reset to zero).
-B--: May be relevant to the recursive transactions for index block splits. I have seen
comments that this flag means the UBA will point to a record holding the previous
content of the ITL entry, but I have not managed to confirm this.
---T: I have seen comments that this means the transaction was active during block
cleanout, but I have not managed to confirm this.
-----------------------------------------------------------------------------------------------------
--//里面提到-B--标识与索引分裂有关.里面提到了recursive transactions,既然是递规事务表示不会回滚的,应该查看索引分裂时可以
--//看到这个标识.转储对应数据块看看。
--//0x10002b7 = set dba 4,695 = alter system dump datafile 4 block 695 = 16777911
--//0x10002b4 = set dba 4,692 = alter system dump datafile 4 block 692 = 16777908
--//0x10002b3 = set dba 4,691 = alter system dump datafile 4 block 691 = 16777907
SCOTT@book> select rowid,id from t1 where id in (1,578,579);
ROWID ID
------------------ ----------
AABQdBAAEAAAAIkAAA 1
AABQdBAAEAAAAK8AAy 578
AABQdBAAEAAAAK8AAx 579
SCOTT@book> alter system checkpoint ;
System altered.
/
/
SCOTT@book> @ rowid AABQdBAAEAAAAK8AAx
OBJECT FILE BLOCK ROW ROWID_DBA DBA TEXT
---------- ---------- ---------- ---------- -------------------- -------------------- ----------------------------------------
329537 4 700 49 0x10002BC 4,700 alter system dump datafile 4 block 700 ;
--//alter system dump datafile 4 block 691;索引的root节点。
Block header dump: 0x010002b3
Object id on Block? Y
seg/obj: 0x50740 csc: 0x03.1dac5765 itc: 1 flg: E typ: 2 - INDEX
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
brn: 0 bdba: 0x10002b0 ver: 0x01 opc: 0
inc: 0 exflg: 0
Itl Xid Uba Flag Lck Scn/Fsc
0x01 0x000a.014.00037e64 0x00c00d30.1297.01 -BU- 1 fsc 0x0000.1dac5767
Branch block dump
=================
header address 140085000411724=0x7f6814b01a4c
kdxcolev 1
KDXCOLEV Flags = - - -
kdxcolok 1
kdxcoopc 0x80: opcode=0: iot flags=--- is converted=Y
kdxconco 1
kdxcosdc 1
kdxconro 1
kdxcofbo 30=0x1e
kdxcofeo 8048=0x1f70
kdxcoavs 8018
kdxbrlmc 16777911=0x10002b7
kdxbrsno 0
kdxbrbksz 8056
kdxbr2urrc 0
row#0[8048] dba: 16777908=0x10002b4
col 0; len 3; (3): c2 03 64 --// id=299
----- end of branch block dump -----
--//注意FLAG=-BU-.
--//alter system dump datafile 4 block 692;
Block header dump: 0x010002b4
Object id on Block? Y
seg/obj: 0x50740 csc: 0x03.1dac5957 itc: 2 flg: E typ: 2 - INDEX
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
brn: 0 bdba: 0x10002b0 ver: 0x01 opc: 0
inc: 0 exflg: 0
Itl Xid Uba Flag Lck Scn/Fsc
0x01 0x000a.014.00037e64 0x00c00d31.1297.02 CB-- 0 scn 0x0003.1dac5767
0x02 0x0002.01d.00002f84 0x00c006bc.032a.1e ---- 1 fsc 0x0000.00000000
Leaf block dump
===============
header address 140085000411748=0x7f6814b01a64
kdxcolev 0
KDXCOLEV Flags = - - -
kdxcolok 0
kdxcoopc 0x80: opcode=0: iot flags=--- is converted=Y
kdxconco 1
kdxcosdc 1
kdxconro 281
kdxcofbo 598=0x256
kdxcofeo 4663=0x1237
kdxcoavs 4065
kdxlespl 0
kdxlende 0
kdxlenxt 0=0x0
kdxleprv 16777911=0x10002b7
kdxledsz 6
kdxlebksz 8032
row#0[4663] flag: ------, lock: 0, len=12, data:(6): 01 00 02 23 00 22
col 0; len 3; (3): c2 03 64
...
row#279[8008] flag: ------, lock: 2, len=12, data:(6): 01 00 02 bc 00 32
col 0; len 3; (3): c2 06 4f --//id=578键值
row#280[8020] flag: ------, lock: 0, len=12, data:(6): 01 00 02 bc 00 31
col 0; len 3; (3): c2 06 50 --//id=579键值
----- end of leaf block dump -----
--//注意看ITL=0x01,flag=CB--. C表示已经提交，B表示递归事务索引分裂。也就是索引分裂不会回滚的。
--//0x0003.1dac5767 = scn(10): 13382735719 = scn(16): 0x31dac5767
SCOTT@book> select current_scn from v$database;
CURRENT_SCN
------------
13382739012
SCOTT@book> select rowid from t1 where id=578;
no rows selected
SCOTT@book> select current_scn from v$database;
CURRENT_SCN
------------
13382739020
SCOTT@book> @ tix
New tracefile_identifier = /u01/app/oracle/diag/rdbms/book/book/trace/book_ora_24916_0004.trc
SCOTT@book> alter system dump logfile '/mnt/ramdisk/book/redo02.log' scn min 13382739012 scn max 13382739020;
System altered.
SCOTT@book> alter system checkpoint ;
System altered.
SCOTT@book> alter system checkpoint ;
System altered.
SCOTT@book> @ tix
New tracefile_identifier = /u01/app/oracle/diag/rdbms/book/book/trace/book_ora_24916_0005.trc
SCOTT@book> alter system dump datafile 4 block 692;
System altered.
--//日志转储：
REDO RECORD - Thread:1 RBA: 0x0004b6.00002a4e.0010 LEN: 0x006c VLD: 0x05
SCN: 0x0003.1dac6449 SUBSCN: 1 11/08/2021 09:29:49
(LWN RBA: 0x0004b6.00002a4e.0010 LEN: 0001 NST: 0001 SCN: 0x0003.1dac6449)
CHANGE #1 TYP:0 CLS:1 AFN:4 DBA:0x010002b4 OBJ:329536 SCN:0x0003.1dac5957 SEQ:1 OP:4.1 ENC:0 RBL:0
Block cleanout record, scn: 0x0003.1dac6449 ver: 0x01 opt: 0x01, entries follow...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
END OF REDO DUMP
--//dba=4,692转储：
Block header dump: 0x010002b4
Object id on Block? Y
seg/obj: 0x50740 csc: 0x03.1dac6449 itc: 2 flg: E typ: 2 - INDEX
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
brn: 0 bdba: 0x10002b0 ver: 0x01 opc: 0
inc: 0 exflg: 0
Itl Xid Uba Flag Lck Scn/Fsc
0x01 0x000a.014.00037e64 0x00c00d31.1297.02 CB-- 0 scn 0x0003.1dac5767
0x02 0x0002.01d.00002f84 0x00c006bc.032a.1e ---- 1 fsc 0x0000.00000000
--//注意看下划线，改变csc的值。ITL槽信息的Scn信息并没有修改，Itl=0x01事务(索引分裂)已经提交。
--//ITL=0x02事务还没有提交。
--//alter system dump datafile 4 block 695
Block header dump: 0x010002b7
Object id on Block? Y
seg/obj: 0x50740 csc: 0x03.1dac5775 itc: 2 flg: E typ: 2 - INDEX
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
brn: 0 bdba: 0x10002b0 ver: 0x01 opc: 0
inc: 0 exflg: 0
Itl Xid Uba Flag Lck Scn/Fsc
0x01 0x000a.014.00037e64 0x00c00d31.1297.01 CB-- 0 scn 0x0003.1dac5767
0x02 0x0000.000.00000000 0x00000000.0000.00 ---- 0 fsc 0x0000.00000000
Leaf block dump
===============
header address 140085000411748=0x7f6814b01a64
kdxcolev 0
KDXCOLEV Flags = - - -
kdxcolok 0
kdxcoopc 0x80: opcode=0: iot flags=--- is converted=Y
kdxconco 1
kdxcosdc 1
kdxconro 298
kdxcofbo 632=0x278
kdxcofeo 4557=0x11cd
kdxcoavs 3925
kdxlespl 0
kdxlende 0
kdxlenxt 16777908=0x10002b4
kdxleprv 0=0x0
kdxledsz 6
kdxlebksz 8032
--//该块的csc应该没有变化。 0x03.1dac5775 与 0x0003.1dac5767 仅仅相差8.
--//数据块呢，oracle如何知道了索引发生分裂没有提交，为什么触摸脏块时每次执行一次Block cleanout record，
--//alter system dump datafile 4 block 700 ;
SCOTT@book> @ tix
New tracefile_identifier = /u01/app/oracle/diag/rdbms/book/book/trace/book_ora_24916_0007.trc
SCOTT@book> alter system dump datafile 4 block 700 ;
System altered.
Block header dump: 0x010002bc
Object id on Block? Y
seg/obj: 0x50741 csc: 0x03.1dac6348 itc: 2 flg: E typ: 1 - DATA
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
brn: 1 bdba: 0x1000220 ver: 0x01 opc: 0
inc: 0 exflg: 0
Itl Xid Uba Flag Lck Scn/Fsc
0x01 0x0002.01d.00002f84 0x00c006bc.032a.1d ---- 1 fsc 0x0000.00000000
0x02 0x000a.00f.00037e62 0x00c00d2f.1297.06 C--- 0 scn 0x0003.1dac5705
--//select /*+ full(t1) */ * from t1 where id=1;
--//alter system dump datafile 4 block 700 ;
Block header dump: 0x010002bc
Object id on Block? Y
seg/obj: 0x50741 csc: 0x03.1dac67b1 itc: 2 flg: E typ: 1 - DATA
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
brn: 1 bdba: 0x1000220 ver: 0x01 opc: 0
inc: 0 exflg: 0
Itl Xid Uba Flag Lck Scn/Fsc
0x01 0x0002.01d.00002f84 0x00c006bc.032a.1d ---- 1 fsc 0x0000.00000000
0x02 0x000a.00f.00037e62 0x00c00d2f.1297.06 C--- 0 scn 0x0003.1dac5705
--//注意看csc前面发生了变化。
--//我估计通过重构块可以知道索引发生了分裂，至于为什么做一次块清除呢我还是不清楚。
--//我找到一个链接blog.sina.com.cn/s/blog_6b8448e70100lvht.html=>索引块分裂引起的交易超时分析(二).
--//帖子是2010年的，说明很早之前就有人遇到类似的问题。
5.总结:
--//唯一索引分裂时估计影响小一点。
--//还是不清楚oracle为什么要这样设计,不管如何事务还是尽早提交。
6.补充：
SCOTT@book> @ viewsessx 'redo size' 58
NAME STATISTIC# VALUE SID
------------------------------ ------------ ------------ ------------
redo size 194 23384 58
SCOTT@book> select * from t1 where id between 510 and 511 ;
ID VC
------------ ----------------------------------------------------------------------------------------------------
510 510xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
511 511xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
SCOTT@book> @ viewsessx 'redo size' 58
NAME STATISTIC# VALUE SID
------------------------------ ------------ ------------ ------------
redo size 194 23492 58
--//可以看出索引范围扫描就不行，redo增加。
SCOTT@book> select * from t1 where id = 510 or id= 511 ;
ID VC
------------ ----------------------------------------------------------------------------------------------------
510 510xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
511 511xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
SCOTT@book> @ viewsessx 'redo size' 58
NAME STATISTIC# VALUE SID
------------------------------ ------------ ------------ ------------
redo size 194 23492 58
--//redo增加。
--//采用or 执行计划是INDEX UNIQUE SCAN。
Plan hash value: 2204817227
------------------------------------------------------------------------------
| Id | Operation | Name | E-Rows |E-Bytes| Cost (%CPU)|
------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | | | 1 (100)|
| 1 | INLIST ITERATOR | | | | |
| 2 | TABLE ACCESS BY INDEX ROWID| T1 | 1 | 65 | 0 (0)|
|* 3 | INDEX UNIQUE SCAN | I_T1_ID | 1 | | 0 (0)|
------------------------------------------------------------------------------
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