揭密一致性读------之UNDO回滚链
揭密一致性读------之UNDO回滚链
Table created.
gyj@OCM> insert into gyj values(1,'AAAAA');
1 row created.
gyj@OCM> commit;
Commit complete.
gyj@OCM> var x refcursor;
gyj@OCM> exec open :x for select * from gyj where id=1;
PL/SQL procedure successfully completed.
gyj@OCM> update gyj set name='BBBBB' where id=1;
1 row updated.
gyj@OCM> commit;
Commit complete.
gyj@OCM> update gyj set name='CCCCC' where id=1;
1 row updated.
gyj@OCM> commit;
Commit complete.
gyj@OCM> update gyj set name='DDDDD' where id=1;
1 row updated.
gyj@OCM> commit;
Commit complete.
gyj@OCM> update gyj set name='EEEEE' where id=1;
1 row updated.
gyj@OCM> print :x;
ID NAME
---------- ----------
1 AAAAA
gyj@OCM> alter system flush buffer_cache;
System altered.
[html]
gyj@OCM> select * from v$transaction;
ADDR XIDUSN XIDSLOT XIDSQN UBAFIL UBABLK UBASQN UBAREC STATUS START_TIME START_SCNB START_SCNW START_UEXT START_UBAFIL START_UBABLK START_UBASQN START_UBAREC SES_ADDR FLAG SPA REC NOU PTX NAME PRV_XIDUSN PRV_XIDSLT PRV_XIDSQN PTX_XIDUSN PTX_XIDSLT PTX_XIDSQN DSCN-B DSCN-W USED_UBLK USED_UREC LOG_IO PHY_IO CR_GET CR_CHANGE START_DATE DSCN_BASE DSCN_WRAP START_SCN DEPENDENT_SCN XID PRV_XID PTX_XID
---------------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------------- -------------------- ---------- ---------- ---------- ------------ ------------ ------------ ------------ ---------------- ---------- --- --- --- --- ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ------------ ---------- ---------- ---------- ------------- ---------------- ---------------- ----------------
000000008FF105A0 7 2 14757 3 84972 1174 21 ACTIVE 11/02/13 18:29:52 13027640 13 3 84972 1174 21 000000009147B7E0 3587 NO NO NO NO 0 0 0 0 0 0 0 0 1 1 11 3 24 0 02-NOV-13 0 0 13027640 0 07000200A5390000 0000000000000000 0000000000000000
sys@OCM> select * from X$KTUXE where KTUXESTA='ACTIVE';
ADDR INDX INST_ID KTUXEUSN KTUXESLT KTUXESQN KTUXERDBF KTUXERDBB KTUXESCNB KTUXESCNW KTUXESTA KTUXECFL KTUXEUEL KTUXEDDBF KTUXEDDBB KTUXEPUSN KTUXEPSLT KTUXEPSQN KTUXESIZ
---------------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------------- ------------------------ ---------- ---------- ---------- ---------- ---------- ---------- ----------
00002AC148607908 304 1 7 2 14757 3 84972 13027640 0 ACTIVE NONE 13 0 0 0 0 0 1
sys@OCM> select header_file,header_block from dba_segments where segment_name='_SYSSMU7_4222772309$';
HEADER_FILE HEADER_BLOCK
----------- ------------
3 224
sys@OCM> select EXTENT_ID,FILE_ID, BLOCK_ID,BYTES,BLOCKS,STATUS from dba_undo_extents where segment_name='_SYSSMU7_4222772309$';
EXTENT_ID FILE_ID BLOCK_ID BYTES BLOCKS STATUS
---------- ---------- ---------- ---------- ---------- ---------
0 3 224 65536 8 EXPIRED
1 3 600 65536 8 EXPIRED
2 3 3200 1048576 128 EXPIRED
3 3 4992 1048576 128 EXPIRED
4 3 6528 1048576 128 EXPIRED
5 3 8192 1048576 128 EXPIRED
6 3 9600 1048576 128 EXPIRED
7 3 11136 1048576 128 EXPIRED
8 3 12800 1048576 128 EXPIRED
9 3 14208 1048576 128 EXPIRED
10 3 15744 1048576 128 EXPIRED
11 3 17408 1048576 128 EXPIRED
12 3 18688 1048576 128 EXPIRED
13 3 84864 8388608 1024 ACTIVE
14 3 178560 8388608 1024 EXPIRED
sys@OCM> select * from v$rollstat;
USN LATCH EXTENTS RSSIZE WRITES XACTS GETS WAITS OPTSIZE HWMSIZE SHRINKS WRAPS EXTENDSAVESHRINK AVEACTIVE STATUS CUREXT CURBLK
---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- --------------- ---------- ----------
0 0 6 385024 8112 0 93 0 385024 0 0 0 0 ONLINE 5 4
1 1 16 14802944 1172136 0 832 0 14802944 0 1 00 104857 ONLINE 15 45
2 2 5 3268608 930888 0 871 0 3268608 0 1 00 104857 ONLINE 3 53
3 0 17 2088960 1175554 0 948 0 2088960 0 16 140 123087 ONLINE 14 56
4 1 17 15851520 981912 0 779 0 15851520 0 1 00 104857 ONLINE 16 45
5 2 24 19259392 581992 0 688 0 19259392 0 1 00 104857 ONLINE 23 81
6 0 3 1171456 807088 0 810 0 1171456 0 1 00 104857 ONLINE 0 4
7 1 15 28434432 246082 1 361 0 28434432 0 0 0 0 ONLINE 13 108
8 2 5 3268608 843906 0 789 0 3268608 0 1 00 104857 ONLINE 4 95
9 0 12 10608640 725944 0 775 0 10608640 0 1 00 104857 ONLINE 3 75
10 1 5 2285568 800262 0 727 0 2285568 0 4 00 109093 ONLINE 2 83
********************************************************************************
Undo Segment: _SYSSMU7_4222772309$ (7)
********************************************************************************
Extent Control Header
-----------------------------------------------------------------
Extent Header:: spare1:
