[20181206]关于一致性读取3.txt
–//简单演示一致性读取以及如何读取undo重构数据块的.我不想转储对应的undo块,解析那些复杂的过程.
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
–//以scott用户登录,执行如下:
create table t (id number,name varchar2(10));
insert into t select 1 id ,lpad(‘a’,10,’a’) name from dual ;
commit ;
–//分析略.
scott@book> select rowid,t.* from t;
rowid id name
—————— ———- ——————–
aaawgdaaeaaaaimaaa 1 aaaaaaaaaa
scott@book> @ rowid aaawgdaaeaaaaimaaa
object file block row rowid_dba dba text
———- ———- ———- ———- ——————– ——————– —————————————-
90525 4 524 0 0x100020c 4,524 alter system dump datafile 4 block 524 ;
sql> alter system set “_smu_debug_mode” = 45;
system altered.
–//可以指定回滚段.要重启才生效.
–//说明之所以这样,主要我发现执行dml使用的回滚段会使用相同的块.
2.建立测试脚本:
$ cat b1.txt
var x refcursor;
set numw 12
select current_scn from v$database;
exec open :x for select * from t where id=1;
pause
alter system flush buffer_cache;
alter system flush buffer_cache;
@ 10046on 12
print :x
@ 10046off
@ pp
quit
$ cat b4.txt
set linesize 300
column name new_value v_rollname
column name noprint
select name from v$rollname where usn=1;
set transaction use rollback segment “&&v_rollname”;
update t set name=lpad(‘b’,9,’b’) where id=1;
@ xid
commit ;
select name from v$rollname where usn=2;
set transaction use rollback segment “&&v_rollname”;
update t set name=lpad(‘c’,8,’c’) where id=1;
@ xid
commit;
select name from v$rollname where usn=3;
set transaction use rollback segment “&&v_rollname”;
update t set name=lpad(‘d’,7,’d’) where id=1;
@ xid
commit ;
select name from v$rollname where usn=4;
set transaction use rollback segment “&&v_rollname”;
update t set name=lpad(‘e’,6,’e’) where id=1;
@ xid
commit ;
column name print
3.执行脚本:
scott@book> @ b1.txt
current_scn
————
13815694556
pl/sql procedure successfully completed.
–//这里暂停执行脚本 b4.txt
system altered.
system altered.
old 1: alter session set events ‘10046 trace name context forever, level &1’
new 1: alter session set events ‘10046 trace name context forever, level 12’
session altered.
id name
———— ——————–
1 aaaaaaaaaa
session altered.
tracefile
——————————————————————————–
/u01/app/oracle/diag/rdbms/book/book/trace/book_ora_38984.trc
scott@book> @ b4.txt
old 1: set transaction use rollback segment “&&v_rollname”
new 1: set transaction use rollback segment “_syssmu1_3724004606$”
transaction set.
1 row updated.
xidusn_xidslot_xidsqn
——————————
1.22.1560
c70 xidusn xidslot xidsqn ubafil ubablk ubasqn ubarec status used_ublk used_urec xid addr start_date flag
———————————————————————- ———- ———- ———- ———- ———- ———- ———- —————- ———- ———- —————- —————- ——————- ———-
alter system dump undo block ‘_syssmu1_3724004606$’ xid 1 22 1560; 1 22 1560 3 1356 768 11 active 1 1 0100160018060000 0000000082360348 2018-12-06 08:48:44 -2.147e+09
alter system dump undo header ‘_syssmu1_3724004606$’;
alter system dump datafile 3 block 1356;
commit complete.
old 1: set transaction use rollback segment “&&v_rollname”
new 1: set transaction use rollback segment “_syssmu2_2996391332$”
transaction set.
1 row updated.
xidusn_xidslot_xidsqn
——————————
2.24.1784
c70 xidusn xidslot xidsqn ubafil ubablk ubasqn ubarec status used_ublk used_urec xid addr start_date flag
———————————————————————- ———- ———- ———- ———- ———- ———- ———- —————- ———- ———- —————- —————- ——————- ———-
alter system dump undo block ‘_syssmu2_2996391332$’ xid 2 24 1784; 2 24 1784 3 1217 559 46 active 1 1 02001800f8060000 0000000082360348 2018-12-06 08:48:44 -2.147e+09
alter system dump undo header ‘_syssmu2_2996391332$’;
alter system dump datafile 3 block 1217;
commit complete.
old 1: set transaction use rollback segment “&&v_rollname”
new 1: set transaction use rollback segment “_syssmu3_1723003836$”
transaction set.
1 row updated.
xidusn_xidslot_xidsqn
——————————
3.18.1777
c70 xidusn xidslot xidsqn ubafil ubablk ubasqn ubarec status used_ublk used_urec xid addr start_date flag
———————————————————————- ———- ———- ———- ———- ———- ———- ———- —————- ———- ———- —————- —————- ——————- ———-
alter system dump undo block ‘_syssmu3_1723003836$’ xid 3 18 1777; 3 18 1777 3 1010 921 52 active 1 1 03001200f1060000 0000000082360348 2018-12-06 08:48:44 -2.147e+09
alter system dump undo header ‘_syssmu3_1723003836$’;
alter system dump datafile 3 block 1010;
commit complete.
old 1: set transaction use rollback segment “&&v_rollname”
new 1: set transaction use rollback segment “_syssmu4_1254879796$”
transaction set.
1 row updated.
xidusn_xidslot_xidsqn
——————————
4.11.1571
c70 xidusn xidslot xidsqn ubafil ubablk ubasqn ubarec status used_ublk used_urec xid addr start_date flag
———————————————————————- ———- ———- ———- ———- ———- ———- ———- —————- ———- ———- —————- —————- ——————- ———-
alter system dump undo block ‘_syssmu4_1254879796$’ xid 4 11 1571; 4 11 1571 3 179 811 45 active 1 1 04000b0023060000 0000000082360348 2018-12-06 08:48:44 -2.147e+09
alter system dump undo header ‘_syssmu4_1254879796$’;
alter system dump datafile 3 block 179;
commit complete.
–//使用的回滚段保存前映像的块的dba是(3,179) (3,1010) (3,1217) (3,1356) [注:从尾部向前看.]
4.分析转储:
$ grep -i “nam=’db file” /u01/app/oracle/diag/rdbms/book/book/trace/book_ora_38984.trc
wait #140008354428832: nam=’db file sequential read’ ela= 12 file#=4 block#=522 blocks=1 obj#=90525 tim=1544057363227135 –//读数据段段头.
wait #140008354428832: nam=’db file scattered read’ ela= 27 file#=4 block#=523 blocks=5 obj#=90525 tim=1544057363227276 –//读数据块,注意blocks=5,包括了dba=4,524.
wait #140008354428832: nam=’db file sequential read’ ela= 10 file#=3 block#=179 blocks=1 obj#=0 tim=1544057363227374 –//修改lpad(‘e’,6,’e’)的事务.
wait #140008354428832: nam=’db file sequential read’ ela= 11 file#=3 block#=1010 blocks=1 obj#=0 tim=1544057363227490 –//修改lpad(‘d’,7,’d’)的事务.
wait #140008354428832: nam=’db file sequential read’ ela= 8 file#=3 block#=1217 blocks=1 obj#=0 tim=1544057363227553 –//修改lpad(‘c’,6,’c’)的事务
wait #140008354428832: nam=’db file sequential read’ ela= 17 file#=3 block#=1356 blocks=1 obj#=0 tim=1544057363227624 –//修改lpad(‘b’,6,’b’)的事务.
sys@book> @ bh 4 524
hladdr dbarfil dbablk class class_type state tch cr_scn_bas cr_scn_wrp cr_uba_fil cr_uba_blk cr_uba_seq ba object_name
—————- ———- ———- ———- —————— ———- ———- ———- ———- ———- ———- ———- —————- ——————–
0000000084d68628 4 524 1 data block cr 1 930792668 3 3 179 811 0000000076b3c000 t
0000000084d68628 4 524 1 data block xcur 0 0 0 0 0 0 0000000078784000 t
–//看看state=’cr’,ba=0000000063c2a000地址指向的块信息:
sys@book> oradebug setmypid
statement processed.
sys@book> oradebug peek 0x76b3c000 8192 1
[076b3c000, 076b3e000) = 0000a206 0100020c 377ac521 00000003 00000000 00000001 0001619d 377ac4f1 00000003 00320002 01000208 0018000a 000052d1 00c001b1 …
sys@book> oradebug tracefile_name
/u01/app/oracle/diag/rdbms/book/book/trace/book_ora_39054.trc
–//检查转储:
*** 2018-12-06 08:53:44.097
processing oradebug command ‘peek 0x76b3c000 8192 1’
[076b3c000, 076b3e000) = 0000a206 0100020c 377ac521 00000003 00000000 …
dump of memory from 0x076b3c014 to 0x076b3e000
076b3c010 00000001 0001619d 377ac4f1 […..a….z7]
076b3c020 00000003 00320002 01000208 0018000a [……2………]
076b3c030 000052d1 00c001b1 00070f3b 00038000 [.r……;…….]
076b3c040 377ac304 00000000 00000000 00000000 [..z7…………]
076b3c050 00000000 00000000 00000000 00000000 […………….]
076b3c060 00000000 00010100 0014ffff 1f731f0f […………..s.]
076b3c070 00001f73 1f0f0001 00000000 00000000 [s……………]
076b3c080 00000000 00000000 00000000 00000000 […………….]
repeat 494 times
076b3df70 2c000000 c1020200 41410a02 41414141 […,……aaaaaa]
076b3df80 41414141 0202002c 420902c1 42424242 [aaaa,……bbbbb]
076b3df90 42424242 0202002c 430802c1 43434343 [bbbb,……ccccc]
076b3dfa0 2c434343 c1020200 44440702 44444444 [ccc,……dddddd]
076b3dfb0 02012c44 0602c102 45454545 002c4545 [d,……eeeeee,.]
076b3dfc0 02c10202 44444407 44444444 0202002c […..ddddddd,…]
076b3dfd0 430802c1 43434343 2c434343 c1020200 […cccccccc,….]
076b3dfe0 42420902 42424242 2c424242 c1020200 [..bbbbbbbbb,….]
076b3dff0 41410a02 41414141 41414141 c5210600 [..aaaaaaaaaa..!.]
*** 2018-12-06 08:53:44.098
oradebug command ‘peek 0x76b3c000 8192 1’ console output:
[076b3c000, 076b3e000) = 0000a206 0100020c 377ac521 00000003 00000000 00000001 0001619d 377ac4f1 00000003 00320002 01000208 0018000a 000052d1 00c001b1 …
–//你可以发现一致性读取如何通过undo重构数据块的信息,就好像反转操作.由于我每次修改长度都不等于原来的长度.这样看到转储的信息包含a,b,c,d,e等字符串2遍.
–//换一种方式转储数据缓存的对应数据块dba=4,524:
sys@book> @ bbvi 4 524
bvi_command
—————————————————————————————————-
bvi -b 4292608 -s 8192 /mnt/ramdisk/book/users01.dbf
xxd -c16 -g 2 -s 4292608 -l 8192 /mnt/ramdisk/book/users01.dbf
dd if=/mnt/ramdisk/book/users01.dbf bs=8192 skip=524 count=1 of=4_524.dd conv=notrunc 2>/dev/null
od -j 4292608 -n 8192 -t x1 -v /mnt/ramdisk/book/users01.dbf
hexdump -s 4292608 -n 8192 -c -v /mnt/ramdisk/book/users01.dbf
alter system dump datafile ‘/mnt/ramdisk/book/users01.dbf’ block 524;
alter session set events ‘immediate trace name set_tsn_p1 level 5’;
alter session set events ‘immediate trace name buffer level 16777740’;
9 rows selected.
sys@book> alter session set events ‘immediate trace name set_tsn_p1 level 5’;
session altered.
sys@book> alter session set events ‘immediate trace name buffer level 16777740’;
session altered.
bh (0x76bf5770) file#: 4 rdba: 0x0100020c (4/524) class: 1 ba: 0x76b3c000
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~//ba地址与前面看到的一致.
set: 65 pool: 3 bsz: 8192 bsi: 0 sflg: 2 pwc: 18,19
dbwrid: 1 obj: 90525 objn: 90525 tsn: 4 afn: 4 hint: f
hash: [0x787f8408,0x84d69f20] lru: [0x84bd22c0,0x783dbee0]
ckptq: [null] fileq: [null] objq: [null] objaq: [null]
st: cr md: null tch: 1
cr: [scn: 0x3.377ac4dc],[xid: 0x4.b.623],[uba: 0xc000b3.32b.2d],[cls: 0x3.377ac520],[sfl: 0x1],[lc: 0x3.377ac4f2]
flags: only_sequential_access
buffer tsn: 4 rdba: 0x0100020c (4/524)
scn: 0x0003.377ac521 seq: 0x00 flg: 0x00 tail: 0xc5210600
frmt: 0x02 chkval: 0x0000 type: 0x06=trans data
hex dump of block: st=0, typ_found=1
dump of memory from 0x0000000076b3c000 to 0x0000000076b3e000
076b3c000 0000a206 0100020c 377ac521 00000003 [……..!.z7….]
076b3c010 00000000 00000001 0001619d 377ac4f1 [………a….z7]
076b3c020 00000003 00320002 01000208 0018000a [……2………]
076b3c030 000052d1 00c001b1 00070f3b 00038000 [.r……;…….]
076b3c040 377ac304 00000000 00000000 00000000 [..z7…………]
076b3c050 00000000 00000000 00000000 00000000 […………….]
076b3c060 00000000 00010100 0014ffff 1f731f0f […………..s.]
076b3c070 00001f73 1f0f0001 00000000 00000000 [s……………]
076b3c080 00000000 00000000 00000000 00000000 […………….]
repeat 494 times
076b3df70 2c000000 c1020200 41410a02 41414141 […,……aaaaaa]
076b3df80 41414141 0202002c 420902c1 42424242 [aaaa,……bbbbb]
076b3df90 42424242 0202002c 430802c1 43434343 [bbbb,……ccccc]
076b3dfa0 2c434343 c1020200 44440702 44444444 [ccc,……dddddd]
076b3dfb0 02012c44 0602c102 45454545 002c4545 [d,……eeeeee,.]
076b3dfc0 02c10202 44444407 44444444 0202002c […..ddddddd,…]
076b3dfd0 430802c1 43434343 2c434343 c1020200 […cccccccc,….]
076b3dfe0 42420902 42424242 2c424242 c1020200 [..bbbbbbbbb,….]
076b3dff0 41410a02 41414141 41414141 c5210600 [..aaaaaaaaaa..!.]
block header dump: 0x0100020c
object id on block? y
seg/obj: 0x1619d csc: 0x03.377ac4f1 itc: 2 flg: e typ: 1 – data
brn: 0 bdba: 0x1000208 ver: 0x01 opc: 0
inc: 0 exflg: 0
itl xid uba flag lck scn/fsc
0x01 0x000a.018.000052d1 0x00c001b1.0f3b.07 c— 0 scn 0x0003.377ac304
0x02 0x0000.000.00000000 0x00000000.0000.00 —- 0 fsc 0x0000.00000000
bdba: 0x0100020c
data_block_dump,data header at 0x76b3c064
===============
tsiz: 0x1f98
hsiz: 0x14
pbl: 0x76b3c064
76543210
flag=——–
ntab=1
nrow=1
frre=-1
fsbo=0x14
fseo=0x1f0f
avsp=0x1f73
tosp=0x1f73
0xe:pti[0] nrow=1 offs=0
0x12:pri[0] offs=0x1f0f
block_row_dump:
tab 0, row 0, @0x1f0f –//这个偏移与第1次插入的问题不同.
tl: 17 fb: –h-fl– lb: 0x0 cc: 2
col 0: [ 2] c1 02
col 1: [10] 41 41 41 41 41 41 41 41 41 41
end_of_block_dump
4.换一种方式:
$ cat b5.txt
alter system flush buffer_cache;
alter system flush buffer_cache;
@ 10046on 12
select * from t as of scn 13815694556 where id=1;
@ 10046off
@ pp
scott@book> @ b5.txt
system altered.
system altered.
old 1: alter session set events ‘10046 trace name context forever, level &1’
new 1: alter session set events ‘10046 trace name context forever, level 12’
session altered.
id name
———- ——————–
1 aaaaaaaaaa
session altered.
tracefile
——————————————————————————–
/u01/app/oracle/diag/rdbms/book/book/trace/book_ora_39134.trc
$ grep -i “nam=’db file” /u01/app/oracle/diag/rdbms/book/book/trace/book_ora_39134.trc
wait #140406431959032: nam=’db file scattered read’ ela= 45 file#=2 block#=416 blocks=8 obj#=272 tim=1544058316954648
wait #140406431959032: nam=’db file scattered read’ ela= 48 file#=2 block#=74816 blocks=8 obj#=272 tim=1544058316954781
wait #140406431959032: nam=’db file scattered read’ ela= 52 file#=2 block#=71376 blocks=8 obj#=270 tim=1544058316954972
–//上面是读 以下部分访问的数据块与前面测试一直.
wait #140406431960096: nam=’db file sequential read’ ela= 11 file#=4 block#=522 blocks=1 obj#=90525 tim=1544058316956075
wait #140406431960096: nam=’db file scattered read’ ela= 38 file#=4 block#=523 blocks=5 obj#=90525 tim=1544058316956220
wait #140406431960096: nam=’db file sequential read’ ela= 17 file#=3 block#=179 blocks=1 obj#=0 tim=1544058316956314
wait #140406431960096: nam=’db file sequential read’ ela= 10 file#=3 block#=1010 blocks=1 obj#=0 tim=1544058316956431
wait #140406431960096: nam=’db file sequential read’ ela= 10 file#=3 block#=1217 blocks=1 obj#=0 tim=1544058316956497
wait #140406431960096: nam=’db file sequential read’ ela= 9 file#=3 block#=1356 blocks=1 obj#=0 tim=1544058316956558
–//前面的3条访问的数据块是:
scott@book> @ which_obj 2 416
owner segment_name partition_name segment_type tablespace_name extent_id file_id block_id bytes blocks relative_fno
—— ——————— ————– —————— ————— ———- ———- ———- ———- ———- ————
sys smon_scn_time_scn_idx index sysaux 0 2 416 65536 8 2
scott@book> @ which_obj 2 74816
owner segment_name partition_name segment_type tablespace_name extent_id file_id block_id bytes blocks relative_fno
—— ——————— ————– —————— ————— ———- ———- ———- ———- ———- ————
sys smon_scn_time_scn_idx index sysaux 1 2 74816 65536 8 2
scott@book> @ which_obj 2 71376
owner segment_name partition_name segment_type tablespace_name extent_id file_id block_id bytes blocks relative_fno
—— ——————— ————– —————— ————— ———- ———- ———- ———- ———- ————
sys smon_scn_to_time_aux cluster sysaux 17 2 71296 1048576 128 2
–//如果建立唯一索引在id字段,你再重复前面的测试,你会发现结果不同,大家可以参考我以前写的:
–//链接:http://blog.itpub.net/267265/viewspace-772101/
–//附上测试脚本:
$ cat xid.sql
column xidusn_xidslot_xidsqn format a30
select dbms_transaction.local_transaction_id() xidusn_xidslot_xidsqn from dual ;
–select xidusn,xidslot,xidsqn,ubafil,ubablk,ubarec, ubasqn,status,used_ublk,used_urec,xid,addr from v$transaction;
select ‘alter system dump undo block ”’
|| (select name
from sys.undo$
where us# = xidusn)
|| ”’ xid ‘
|| xidusn
|| ‘ ‘
|| xidslot
|| ‘ ‘
|| xidsqn
|| ‘;’
|| chr (10)
|| ‘alter system dump undo header ”’
|| (select name
from sys.undo$
where us# = xidusn)
|| ””
|| ‘;’
|| chr (10)
|| ‘alter system dump datafile ‘
|| ubafil
|| ‘ block ‘
|| ubablk
|| ‘;’
c70
,xidusn
,xidslot
,xidsqn
,ubafil
,ubablk
,ubasqn
,ubarec
,status
,used_ublk
,used_urec
,xid
,addr
,start_date
,flag
from v$transaction;
$ cat bbvi.sql
column bvi_command format a100
select ‘bvi -b ‘|| &2*block_size||’ -s ‘||block_size||’ ‘||name bvi_command from v$datafile where file#=&1
union all
select ‘xxd -c16 -g 2 -s ‘|| &2*block_size||’ -l ‘||block_size||’ ‘||name bvi_command from v$datafile where file#=&1
union all
select ‘dd if=’||name||’ bs=’||block_size||’ skip=’||&2||’ count=1 of=’||&1||’_’||&2||’.dd conv=notrunc 2>/dev/null’ bvi_command from v$datafile where file#=&1
union all
select ‘od -j ‘||&2*block_size||’ -n ‘||block_size||’ -t x1 -v ‘||name bvi_command from v$datafile where file#=&1
union all
select ‘hexdump -s ‘||&2*block_size||’ -n ‘||block_size||’ -c -v ‘||name bvi_command from v$datafile where file#=&1
union all
select ‘alter system dump datafile ‘||””||name||””||’ block ‘||&2||’;’ from v$datafile where file#=&1
union all
select ” bvi_command from dual
union all
select ‘alter session set events ”immediate trace name set_tsn_p1 level ‘|| to_char(ts#+1)||”’;’ bvi_command from sys.ts$
where name in (select tablespace_name from v$datafile_header where file# = &&1)
union all
select ‘alter session set events ”immediate trace name buffer level ‘||dbms_utility.make_data_block_address(&&1,&&2)||”’;’ bvi_command from dual;