[20181116]18c DML 日志优化.txt

1.环境:
xxxxxxxx> select banner_full from v$version;
BANNER_FULL
-----------------------------------------------------------------------------
Oracle Database 18c Enterprise Edition Release 18.0.0.0.0 - Production
Version 18.3.0.0.0

2.建立测试脚本:
xxxxxxxx> create table t as select rownum id ,lpad('y',200,'y') v1,lpad('z',100,'z') v2 from dual connect by level<=100;
Table created.

xxxxxxxx> select dump('x',16),dump('y',16),dump('z',16) from dual ;
DUMP('X',16) DUMP('Y',16) DUMP('Z',16)
-------------------------------- -------------------------------- --------------------------------
Typ=96 Len=1: 78 Typ=96 Len=1: 79 Typ=96 Len=1: 7a

xxxxxxxx> @ viewsess redo%size
NAME                               STATISTIC#          VALUE        SID
---------------------------------- ---------- -------------- ----------
redo size                                 293            684        258
redo size for lost write detection        295              0        258
redo size for direct writes               296              0        258
redo write size count (   4KB)            321              0        258
redo write size count (   8KB)            322              0        258
redo write size count ( 16KB)            323              0        258
redo write size count ( 32KB)            324              0        258
redo write size count ( 64KB)            325              0        258
redo write size count ( 128KB)            326              0        258
redo write size count ( 256KB)            327              0        258
redo write size count ( 512KB)            328              0        258
redo write size count (1024KB)            329              0        258
redo write size count (inf)               330              0        258
IMU Redo allocation size                  736              0        258
14 rows selected.

--//建立测试脚本a.txt
column member new_value v_member
column member noprint
set numw 12
alter system switch logfile ;
--//alter system archive log current;
--//12c以上不允许在pluggable database执行这条命令.注这个库没有打开归档,alter system archive log current;会报错.
--//采用alter system switch logfile ;.
SELECT member FROM v$log a, v$logfile b WHERE a.group#(+) = b.group# and a.STATUS='CURRENT' and rownum=1;

column curr1 new_value v_curr1
select current_scn curr1 from v$database;

--//以下操作DML内容:
update t set v1=lpad('y',200,'y') ,v2=lpad('z',100,'z');
commit ;

exec dbms_session.sleep(3);

column curr2 new_value v_curr2
select current_scn curr2 from v$database;

prompt exec DBMS_LOGMNR.START_LOGMNR(STARTSCN => &&v_curr1 ,ENDSCN => &&v_curr2 ,OPTIONS => DBMS_LOGMNR.DICT_FROM_ONLINE_CATALOG + DBMS_LOGMNR.CONTINUOUS_MINE);
prompt alter system dump logfile '&&v_member' scn min &&v_curr1 scn max &&v_curr2;
alter system dump logfile '&&v_member' scn min &&v_curr1 scn max &&v_curr2;

--//执行脚本a.txt:
xxxxxxxx> @ a.txt
System altered.
CURR1
------------
1336662128
100 rows updated.

Commit complete.

PL/SQL procedure successfully completed.
CURR2
------------
1336662131

exec DBMS_LOGMNR.START_LOGMNR(STARTSCN => 1336662128 ,ENDSCN => 1336662131 ,OPTIONS => DBMS_LOGMNR.DICT_FROM_ONLINE_CATALOG + DBMS_LOGMNR.CONTINUOUS_MINE)
alter system dump logfile '+DATA/ORCLCDB/ONLINELOG/group_2.264.985030477' scn min 1336662128 scn max 1336662131

System altered.

xxxxxxxx> @ viewsess redo%size
NAME                               STATISTIC#          VALUE          SID
---------------------------------- ---------- -------------- ------------
redo size                                 293          23692          258
redo size for lost write detection        295              0          258
redo size for direct writes               296              0          258
redo write size count (   4KB)            321              0          258
redo write size count (   8KB)            322              0          258
redo write size count ( 16KB)            323              0          258
redo write size count ( 32KB)            324              0          258
redo write size count ( 64KB)            325              0          258
redo write size count ( 128KB)            326              0          258
redo write size count ( 256KB)            327              0          258
redo write size count ( 512KB)            328              0          258
redo write size count (1024KB)            329              0          258
redo write size count (inf)               330              0          258
IMU Redo allocation size                  736          49012          258

14 rows selected.

--//日志大小 23692-648 = 23044 ,大约22K.
--//如果你查询转储文件,你可以发现一个奇特的信息,你根本找不到yyyy,zzzz相关的字符串信息.
--//也就是如果dml字段前后两者一样,日志根本没有记录.

3.修改dml语句重复测试:
$ cat a.txt
..
update t set v1=lpad('z',200,'z') ,v2=lpad('y',100,'y');
commit ;
...

--//执行a.txt
xxxxxxxx> @ viewsess redo%size
NAME                               STATISTIC#          VALUE        SID
---------------------------------- ---------- -------------- ----------
redo size                                 293            684        258
redo size for lost write detection        295              0        258
redo size for direct writes               296              0        258
redo write size count (   4KB)            321              0        258
redo write size count (   8KB)            322              0        258
redo write size count ( 16KB)            323              0        258
redo write size count ( 32KB)            324              0        258
redo write size count ( 64KB)            325              0        258
redo write size count ( 128KB)            326              0        258
redo write size count ( 256KB)            327              0        258
redo write size count ( 512KB)            328              0        258
redo write size count (1024KB)            329              0        258
redo write size count (inf)               330              0        258
IMU Redo allocation size                  736              0        258
14 rows selected.

xxxxxxxx> @ a.txt
System altered.
CURR1
------------
1336662429
100 rows updated.
Commit complete.

PL/SQL procedure successfully completed.
CURR2
------------
1336662432

exec DBMS_LOGMNR.START_LOGMNR(STARTSCN => 1336662429 ,ENDSCN => 1336662432 ,OPTIONS => DBMS_LOGMNR.DICT_FROM_ONLINE_CATALOG + DBMS_LOGMNR.CONTINUOUS_MINE)
alter system dump logfile '+DATA/ORCLCDB/ONLINELOG/group_3.262.985030477' scn min 1336662429 scn max 1336662432
System altered.

xxxxxxxx> @ viewsess redo%size
NAME                               STATISTIC#          VALUE          SID
---------------------------------- ---------- -------------- ------------
redo size                                 293          73948          258
redo size for lost write detection        295              0          258
redo size for direct writes               296              0          258
redo write size count (   4KB)            321              0          258
redo write size count (   8KB)            322              0          258
redo write size count ( 16KB)            323              0          258
redo write size count ( 32KB)            324              0          258
redo write size count ( 64KB)            325              0          258
redo write size count ( 128KB)            326              0          258
redo write size count ( 256KB)            327              0          258
redo write size count ( 512KB)            328              0          258
redo write size count (1024KB)            329              0          258
redo write size count (inf)               330              0          258
IMU Redo allocation size                  736          36236          258
14 rows selected.

--//日志大小73948-648 = 73300,至少72K,比原来增加不少.
--//你可以看到如下:
REDO RECORD - Thread:1 RBA: 0x0008b3.0000002c.0134 LEN: 0x00e0 VLD: 0x01 CON_UID: 1
SCN: 0x000000004fabd870 SUBSCN: 2 11/16/2018 10:30:36
CHANGE #1 CON_ID:1 TYP:0 CLS:24 AFN:4 DBA:0x010008de OBJ:4294967295 SCN:0x000000004fabd870 SEQ:96 OP:5.1 ENC:0 RBL:0 FLG:0x0000
ktudb redo: siz: 68 spc: 866 flg: 0x0022 seq: 0x0ba1 rec: 0x69
            xid: 0x0004.004.00002086
ktubu redo: slt: 4 rci: 104 opc: 11.1 objn: 104890 objd: 104890 tsn: 0
Undo type: Regular undo       Undo type: Last buffer split: No
Tablespace Undo: No
             0x00000000
KDO undo record:
KTB Redo
op: 0x02 ver: 0x01
compat bit: 4 (post-11) padding: 1
op: C uba: 0x010008de.0ba1.68
KDO Op code: LKR row dependencies Disabled
ktudb redo: siz: 68 spc: 656 flg: 0x0022 seq: 0x0ba1 rec: 0x6c
op: F xid: 0x0006.00d.00002131    uba: 0x010000c8.0b0c.01
Block cleanout record, scn: 0x000000004fabd99d ver: 0x01 opt: 0x02 bigscn: Y compact: Y spare: 00000000, entries follow...
itli: 3 flg: (opt=2 whr=1) scn: 0x000000004fabd871
Array Update of 20 rows:
tabn: 0 slot: 0(0x0) flag: 0x2c lock: 1 ckix: 0
ncol: 3 nnew: 2 size: 0
KDO Op code: 21 row dependencies Disabled
xtype: XAxtype KDO_KDOM2 flags: 0x00000080 bdba: 0x0041af39 hdba: 0x0041af38
itli: 1 ispac: 0 maxfr: 4863
vect = 3
col 1: [200]
7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a
7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a
7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a
7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a
7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a
7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a
7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a
7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a 7a
col 2: [100]
79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79
79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79
79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79
79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79
tabn: 0 slot: 1(0x1) flag: 0x2c lock: 1 ckix: 0

4.修改dml语句重复测试:
$ cat a.txt
..
update t set v1=lpad('z',200,'z') ,v2=lpad('x',100,'x');
commit ;
...

--//v1字段修改前后一样,v2字段前后不同,开始是lpad('y',100,'y')后面变成lpad('x',100,'x').

xxxxxxxx> @ viewsess redo%size
NAME STATISTIC# VALUE SID
----------- ---------- -------------- ----------
redo size 293 684 258
....

xxxxxxxx> @ a.txt
System altered.
CURR1
------------
1336662656
100 rows updated.
Commit complete.
PL/SQL procedure successfully completed.
CURR2
------------
1336662659

exec DBMS_LOGMNR.START_LOGMNR(STARTSCN => 1336662656 ,ENDSCN => 1336662659 ,OPTIONS => DBMS_LOGMNR.DICT_FROM_ONLINE_CATALOG + DBMS_LOGMNR.CONTINUOUS_MINE)
alter system dump logfile '+DATA/ORCLCDB/ONLINELOG/group_1.265.985030477' scn min 1336662656 scn max 1336662659
System altered.

xxxxxxxx> @ viewsess redo%size
NAME STATISTIC# VALUE SID
--------- ---------- -------------- ------------
redo size 293 48340 258
....

--//日志大小48340-648 = 47692,47K上下.
--//检查跟踪文件你可以发现:
REDO RECORD - Thread:1 RBA: 0x0008b5.0000005f.0040 LEN: 0x01d0 VLD: 0x01 CON_UID: 1
SCN: 0x000000004fabda80 SUBSCN:1176 11/16/2018 10:44:53
CHANGE #1 CON_ID:1 TYP:0 CLS:18 AFN:4 DBA:0x01000087 OBJ:4294967295 SCN:0x000000004fabda80 SEQ:27 OP:5.1 ENC:0 RBL:0 FLG:0x0000
ktudb redo: siz: 188 spc: 3282 flg: 0x0022 seq: 0x0b4d rec: 0x1b
            xid: 0x0001.002.000020c9
ktubu redo: slt: 2 rci: 26 opc: 11.1 objn: 104890 objd: 104890 tsn: 0
Undo type: Regular undo       Undo type: Last buffer split: No
Tablespace Undo: No
             0x00000000
KDO undo record:
KTB Redo
op: 0x02 ver: 0x01
compat bit: 4 (post-11) padding: 1
op: C uba: 0x01000087.0b4d.1a
KDO Op code: URP row dependencies Disabled
xtype: XA flags: 0x00000000 bdba: 0x0041af3d hdba: 0x0041af38
itli: 2 ispac: 0 maxfr: 4863
tabn: 0 slot: 7(0x7) flag: 0x2c lock: 0 ckix: 0
ncol: 3 nnew: 1 size: 0
col 2: [100]
79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79
79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79
79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79
79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79 79
CHANGE #2 CON_ID:1 TYP:0 CLS:1 AFN:1 DBA:0x0041af3d OBJ:104890 SCN:0x000000004fabda80 SEQ:8 OP:11.5 ENC:0 RBL:0 FLG:0x0000
KTB Redo
op: 0x02 ver: 0x01
compat bit: 4 (post-11) padding: 1
op: C uba: 0x01000087.0b4d.1b
KDO Op code: URP row dependencies Disabled
xtype: XA flags: 0x00000000 bdba: 0x0041af3d hdba: 0x0041af38
itli: 2 ispac: 0 maxfr: 4863
tabn: 0 slot: 7(0x7) flag: 0x2c lock: 2 ckix: 0
ncol: 3 nnew: 1 size: 0
col 2: [100]
78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78
78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78
78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78
78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78 78

--//没有字符z相关内容(7a 7a).

5.总结:
--//你可以发现oracle 18c在dml下修改字段前后如果信息不变,日志根本没有记录,这样一定程度减少日志大小.

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[20181116]18c DML 日志优化.txt

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