事務槽小記

oracle在對錶進行多事務插入時，採用的是分佈式多數據塊插入，oracle表初始事務槽數量是ini_trans爲2，最多兩個事務對同一個數據塊進行插入，而其餘的事務則插入到新塊中，這樣就不會產生事務槽的爭用。

會話一

SQL> insert into scott.t1 values (1);
insert into scott.t1 values (2);
insert into scott.t1 values (3);
insert into scott.t1 values (4);
insert into scott.t1 values (5);

SQL> select id,dbms_rowid.rowid_relative_fno(rowid),dbms_rowid.rowid_block_number(rowid) from scott.t1;

    ID      DBMS_ROWID.ROWID_RELATIVE_FNO(ROWID) DBMS_ROWID.ROWID_BLOCK_NUMBER(ROWID)
----------  ------------------------------------ ------------------------------------
         1                                    4                                                              171
         2                                    4                                                              171
         3                                    4                                                              171
         4                                    4                                                          171
         5                                    4                                                          171


會話2

SQL> insert into scott.t1 values (5);
insert into scott.t1 values (6);
insert into scott.t1 values (7);

SQL> select id,dbms_rowid.rowid_relative_fno(rowid),dbms_rowid.rowid_block_number(rowid) from scott.t1;

   ID       DBMS_ROWID.ROWID_RELATIVE_FNO(ROWID) DBMS_ROWID.ROWID_BLOCK_NUMBER(ROWID)
---------- ------------------------------------ ------------------------------------
         5                                    4                                                             173
         6                                    4                                                             173
         7                                    4                                                             173


會話3

SQL> insert into scott.t1 values (8);
SQL> select id,dbms_rowid.rowid_relative_fno(rowid),dbms_rowid.rowid_block_number(rowid) from scott.t1;

        ID DBMS_ROWID.ROWID_RELATIVE_FNO(ROWID) DBMS_ROWID.ROWID_BLOCK_NUMBER(ROWID)
---------- ------------------------------------ ------------------------------------
         8                                    4                                                             172

SQL> alter system dump datafile 4 block min 171 block max 173;
SQL> ho vim /opt/app/oracle/diag/rdbms/db2/db2/trace/db2_ora_18916.trc
buffer tsn: 4 rdba: 0x010000ab (4/171)
 seg/obj: 0x12160  csc: 0x00.5a3ec5  itc: 2  flg: E  typ: 1 - DATA
     brn: 0  bdba: 0x10000a8 ver: 0x01 opc: 0
     inc: 0  exflg: 0
 Itl           Xid                  Uba         Flag  Lck        Scn/Fsc
0x01   0x0009.01c.0000031c  0x00c0024c.00d0.10  ----    5  fsc 0x0000.00000000
0x02   0x0000.000.00000000  0x00000000.0000.00  ----    0  fsc 0x0000.00000000
block_row_dump:
tl: 6 fb: --H-FL-- lb: 0x1  cc: 1
col  0: [ 2]  c1 02
tab 0, row 1, @0x1f8c
tl: 6 fb: --H-FL-- lb: 0x1  cc: 1
col  0: [ 2]  c1 03
tab 0, row 2, @0x1f86
tl: 6 fb: --H-FL-- lb: 0x1  cc: 1
col  0: [ 2]  c1 04
tab 0, row 3, @0x1f80
tl: 6 fb: --H-FL-- lb: 0x1  cc: 1
col  0: [ 2]  c1 05
tab 0, row 4, @0x1f7a
tl: 6 fb: --H-FL-- lb: 0x1  cc: 1
col  0: [ 2]  c1 06


buffer tsn: 4 rdba: 0x010000ac (4/172)
 seg/obj: 0x12160  csc: 0x00.5a3e7e  itc: 2  flg: E  typ: 1 - DATA
     brn: 0  bdba: 0x10000a8 ver: 0x01 opc: 0
     inc: 0  exflg: 0

 Itl           Xid                  Uba         Flag  Lck        Scn/Fsc
0x01   0x0005.021.00000362  0x00c002e4.010b.01  ----    1  fsc 0x0000.00000000
0x02   0x0000.000.00000000  0x00000000.0000.00  ----    0  fsc 0x0000.00000000

block_row_dump:
tab 0, row 0, @0x1f92
tl: 6 fb: --H-FL-- lb: 0x1  cc: 1
col  0: [ 2]  c1 09

buffer tsn: 4 rdba: 0x010000ad (4/173)
 seg/obj: 0x12160  csc: 0x00.5a3e7e  itc: 2  flg: E  typ: 1 - DATA
     brn: 0  bdba: 0x10000a8 ver: 0x01 opc: 0
     inc: 0  exflg: 0

 Itl           Xid                  Uba         Flag  Lck        Scn/Fsc
0x01   0x000c.016.00000017  0x00c007e6.001f.05  ----    3  fsc 0x0000.00000000
0x02   0x0000.000.00000000  0x00000000.0000.00  ----    0  fsc 0x0000.00000000
block_row_dump:
tab 0, row 0, @0x1f92
tl: 6 fb: --H-FL-- lb: 0x1  cc: 1
col  0: [ 2]  c1 06
tab 0, row 1, @0x1f8c
tl: 6 fb: --H-FL-- lb: 0x1  cc: 1
col  0: [ 2]  c1 07
tab 0, row 2, @0x1f86
tl: 6 fb: --H-FL-- lb: 0x1  cc: 1
col  0: [ 2]  c1 08
可以看出多事務插入時，採用了多個塊插入，每個數據塊都產生了兩個事務槽，使用了其中一個，每個事務槽的修改對應了所修改的行。

update時當同時修改一個數據塊中的行時，每個回話都會在塊中有一個對應的事務槽，max_trans默認是255，發生ITL的爭用比較少；

SQL> declare
  2  begin
  3  for i in 1..10 loop
  4  insert into scott.t1 values (i);
  5  end loop;
  6  commit;
  7  end;
  8  /

SQL> select id,dbms_rowid.rowid_relative_fno(rowid),dbms_rowid.rowid_block_number(rowid) from scott.t1;

        ID DBMS_ROWID.ROWID_RELATIVE_FNO(ROWID) DBMS_ROWID.ROWID_BLOCK_NUMBER(ROWID)
---------- ------------------------------------ ------------------------------------
         1                                    4                                  171
         2                                    4                                  171
         3                                    4                                  171
         4                                    4                                  171
         5                                    4                                  171
         6                                    4                                  171
         7                                    4                                  171
         8                                    4                                  171
         9                                    4                                  171
        10                                    4                                  171

會話1
SQL> update scott.t1 set idid =id where id in (1,2,3,4);

4 rows updated.

會話2
SQL> update scott.t1 set idid =id where id in (5,6,7,8);

4 rows updated.

會話3
SQL> update scott.t1 set idid =id where id in (9,10);

2 rows updated.

SQL> alter system dump datafile 4 block 171;

SQL> ho vim /opt/app/oracle/diag/rdbms/db2/db2/trace/db2_ora_18916.trc
Start dump data blocks tsn: 4 file#:4 minblk 171 maxblk 171

 Object id on Block? Y
 seg/obj: 0x12162  csc: 0x00.5a44d4  itc: 3  flg: E  typ: 1 - DATA
     brn: 0  bdba: 0x10000a8 ver: 0x01 opc: 0
     inc: 0  exflg: 0

 Itl           Xid                  Uba         Flag  Lck        Scn/Fsc
0x01   0x000a.00c.0000028d  0x00c000bd.00dd.07  ----    4  fsc 0x0000.00000000
0x02   0x0008.007.000003f8  0x00c0037a.00c5.06  ----    4  fsc 0x0000.00000000
0x03   0x0003.006.0000033c  0x00c00c9b.0175.01  ----    2  fsc 0x0000.00000000

block_row_dump:
tab 0, row 0, @0x1f7a
tl: 6 fb: --H-FL-- lb: 0x2  cc: 1
col  0: [ 2]  c1 02
tab 0, row 1, @0x1f74
tl: 6 fb: --H-FL-- lb: 0x2  cc: 1
col  0: [ 2]  c1 03
tab 0, row 2, @0x1f6e
tl: 6 fb: --H-FL-- lb: 0x2  cc: 1
col  0: [ 2]  c1 04
tab 0, row 3, @0x1f68
tl: 6 fb: --H-FL-- lb: 0x2  cc: 1
col  0: [ 2]  c1 05
tab 0, row 4, @0x1f62
tl: 6 fb: --H-FL-- lb: 0x1  cc: 1
col  0: [ 2]  c1 06
tab 0, row 5, @0x1f5c
tl: 6 fb: --H-FL-- lb: 0x1  cc: 1
col  0: [ 2]  c1 07
tab 0, row 6, @0x1f56
tl: 6 fb: --H-FL-- lb: 0x1  cc: 1
col  0: [ 2]  c1 08
tab 0, row 7, @0x1f50
tl: 6 fb: --H-FL-- lb: 0x1  cc: 1
col  0: [ 2]  c1 09
tab 0, row 8, @0x1f4a
tl: 6 fb: --H-FL-- lb: 0x3  cc: 1
col  0: [ 2]  c1 0a
tab 0, row 9, @0x1f44
tl: 6 fb: --H-FL-- lb: 0x3  cc: 1
col  0: [ 2]  c1 0b
可以看到，每個UPDATE的會話都有一個事務槽對應，前兩個會話的事務槽每個對應4行，第三個對應2行

事務槽（事務，是否提交，鎖定）

事務正在使用的回滾段，轉向 http://rilee.blog.51cto.com/467020/772463