[20171113]修改表结构删除列相关问题3.txt

[20171113]修改表结构删除列相关问题3.txt

--//维护表结构删除字段一般都是先
ALTER TABLE <table_name> SET UNUSED (<column_name>);

--//然后等空闲时候删除列.
ALTER TABLE <table_name> DROP UNUSED COLUMNS CHECKPOINT <n>;

--//参考文档:
https://docs.oracle.com/cd/E11882_01/server.112/e25494/tables.htm#ADMIN11662

Removing Unused Columns

The ALTER TABLE...DROP UNUSED COLUMNS statement is the only action allowed on unused columns. It physically removes
unused columns from the table and reclaims disk space.

In the ALTER TABLE statement that follows, the optional clause CHECKPOINT is specified. This clause causes a checkpoint
to be applied after processing the specified number of rows, in this case 250. Checkpointing cuts down on the amount of
undo logs accumulated during the drop column operation to avoid a potential exhaustion of undo space.

ALTER TABLE hr.admin_emp DROP UNUSED COLUMNS CHECKPOINT 250;
 
--//从文档上可以看出加入CHECKPOINT关键字可以一定程度减少undo空间的消耗.

--//测试看看使用CHECKPOINT <n>的情况.如果执行中断会出现什么情况呢?会回滚吗,oracle如何处理这些细节问题.而且这个时候sys.col$并不能修改.
--//因为这些修改没有完成.通过测试理解这些问题.

1.环境:

SCOTT@book> @ &r/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

create table t (id number,v1 varchar2(5),v2 varchar2(10));
insert into t select rownum,lpad('a',5,'a'),lpad('b',10,'b') from xmltable('1 to 1000000');
commit;

SCOTT@book> SELECT obj#,col#, segcol#, name, intcol#, type#,PROPERTY FROM sys.col$ WHERE obj# IN (SELECT object_id FROM dba_objects WHERE object_name = 'T' AND owner = user);
        OBJ#         COL#      SEGCOL# NAME                      INTCOL#        TYPE#     PROPERTY
------------ ------------ ------------ -------------------- ------------ ------------ ------------
       90622            1            1 ID                              1            2            0
       90622            2            2 V1                              2            1            0
       90622            3            3 V2                              3            1            0

SCOTT@book> ALTER TABLE t SET UNUSED (v1);
Table altered.

SCOTT@book> SELECT obj#,col#, segcol#, name, intcol#, type#,PROPERTY FROM sys.col$ WHERE obj# IN (SELECT object_id FROM dba_objects WHERE object_name = 'T' AND owner = user);
        OBJ#         COL#      SEGCOL# NAME                                INTCOL#        TYPE#     PROPERTY
------------ ------------ ------------ ------------------------------ ------------ ------------ ------------
       90622            1            1 ID                                        1            2            0
       90622            0            2 SYS_C00002_17111311:56:47$                2            1        32800
       90622            2            3 V2                                        3            1            0

COTT@book> @ &r/spid
         SID      SERIAL# PROCESS                  SERVER    SPID       PID    P_SERIAL# C50
------------ ------------ ------------------------ --------- ------ ------- ------------ --------------------------------------------------
          67           93 48102                    DEDICATED 48103       29           35 alter system kill session '67,93' immediate;

--// 记下进程号spid=48103

2.执行DROP UNUSED COLUMNS:
--//session 1:
ALTER TABLE t DROP UNUSED COLUMNS CHECKPOINT 10;

--//session 2, 在命令行执行:
$ kill -l
 1) SIGHUP       2) SIGINT       3) SIGQUIT      4) SIGILL
 5) SIGTRAP      6) SIGABRT      7) SIGBUS       8) SIGFPE
 9) SIGKILL     10) SIGUSR1     11) SIGSEGV     12) SIGUSR2
13) SIGPIPE     14) SIGALRM     15) SIGTERM     16) SIGSTKFLT
17) SIGCHLD     18) SIGCONT     19) SIGSTOP     20) SIGTSTP
21) SIGTTIN     22) SIGTTOU     23) SIGURG      24) SIGXCPU
25) SIGXFSZ     26) SIGVTALRM   27) SIGPROF     28) SIGWINCH
29) SIGIO       30) SIGPWR      31) SIGSYS      34) SIGRTMIN
35) SIGRTMIN+1  36) SIGRTMIN+2  37) SIGRTMIN+3  38) SIGRTMIN+4
39) SIGRTMIN+5  40) SIGRTMIN+6  41) SIGRTMIN+7  42) SIGRTMIN+8
43) SIGRTMIN+9  44) SIGRTMIN+10 45) SIGRTMIN+11 46) SIGRTMIN+12
47) SIGRTMIN+13 48) SIGRTMIN+14 49) SIGRTMIN+15 50) SIGRTMAX-14
51) SIGRTMAX-13 52) SIGRTMAX-12 53) SIGRTMAX-11 54) SIGRTMAX-10
55) SIGRTMAX-9  56) SIGRTMAX-8  57) SIGRTMAX-7  58) SIGRTMAX-6
59) SIGRTMAX-5  60) SIGRTMAX-4  61) SIGRTMAX-3  62) SIGRTMAX-2
63) SIGRTMAX-1  64) SIGRTMAX

--//19 是 stop,18是cout,9 kill.我直接使用-9 kill进程.
--//先写下命令,避免手忙脚乱.先在session 1发出ALTER TABLE t DROP UNUSED COLUMNS CHECKPOINT 10;,然后切换到session 2执行如下命令.
$ kill -9 48103

--//session 1:
SCOTT@book> ALTER TABLE t DROP UNUSED COLUMNS CHECKPOINT 10;
ALTER TABLE t DROP UNUSED COLUMNS CHECKPOINT 10
*
ERROR at line 1:
ORA-03113: end-of-file on communication channel
Process ID: 48103
Session ID: 67 Serial number: 93

SCOTT@book> select * from t where rownum<=10;
select * from t where rownum<=10
              *
ERROR at line 1:
ORA-12986: columns in partially dropped state. Submit ALTER TABLE DROP COLUMNS CONTINUE

--  //可以发现无法select,也就是要Submit ALTER TABLE DROP COLUMNS CONTINUE.

SCOTT@book>  ALTER TABLE t DROP UNUSED COLUMNS CHECKPOINT 1000;
 ALTER TABLE t DROP UNUSED COLUMNS CHECKPOINT 1000
             *
ERROR at line 1:
ORA-12986: columns in partially dropped state. Submit ALTER TABLE DROP COLUMNS CONTINUE

$ oerr ora 12986
12986, 00000, "columns in partially dropped state. Submit ALTER TABLE DROP COLUMNS CONTINUE"
// *Cause:  An attempt was made to access a table with columns in partially
//          dropped state (i.e., drop column operation was interrupted).
// *Action: Submit ALTER TABLE DROP COLUMNS CONTINUE to complete the drop
//          column operation before accessing the table.

--//一旦出现这样的情况,就不能在使用CHECKPOINT参数.而是执行:

SCOTT@book> ALTER TABLE t DROP COLUMNS CONTINUE;
Table altered.

SCOTT@book> select * from t where rownum<=1;
        ID V2
---------- ----------
       563 bbbbbbbbbb

--ok. 问题在于oracle如何知道发生了中断,重新产生问题跟踪看看(步骤略).

SCOTT@book> @ &r/10046on 12
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.

SCOTT@book> select * from t where rownum<=1;
select * from t where rownum<=1
              *
ERROR at line 1:
ORA-12986: columns in partially dropped state. Submit ALTER TABLE DROP COLUMNS CONTINUE

SCOTT@book> @ &r/10046off
Session altered.

--//看不出问题.没有任何线索.

SYS@book> select * from sys.tab$  where obj#=90622;
...省略...
SP2-0784: Invalid or incomplete character beginning 0xEF returned

--//报SP2-0784错误.

SYS@book> host oerr  SP2 0784
00784,0, "Invalid or incomplete character beginning 0x%02X returned\n"
// *Cause:  Attempted to return a string from the database that contained
//          an invalid or incomplete character.
// *Action: Replace the invalid or incomplete string in the database with
//          a valid or complete string.

--//一个一个字段查询确定,问题在spare4字段上.

SYS@book> select SPARE4 from sys.tab$  where obj#=90622;
SPARE4
-----------------------------------------------------------------
SP2-0784: Invalid or incomplete character beginning 0xEF returned

SCOTT@book> select dump(SPARE4,16) c30 ,spare6 from sys.tab$  where obj#=90622;
C30                            SPARE6
------------------------------ --------------------
Typ=1 Len=6: 1,0,3,e1,0,ef     2017-11-13 03:56:47

--//注意后面有一个ef表示.

--//再建立一个表T1 对比看看.

SCOTT@book> create table t1 (id number,v1 varchar2(5),v2 varchar2(10));
Table created.

SCOTT@book> insert into t1 select rownum,lpad('a',5,'a'),lpad('b',10,'b') from xmltable('1 to 100000');
100000 rows created.

SCOTT@book> commit ;
Commit complete.

SCOTT@book> SELECT obj#,col#, segcol#, name, intcol#, type#,PROPERTY FROM sys.col$ WHERE obj# IN (SELECT object_id FROM dba_objects WHERE object_name = 'T1' AND owner = user);
      OBJ#       COL#    SEGCOL# NAME                    INTCOL#      TYPE#   PROPERTY
---------- ---------- ---------- -------------------- ---------- ---------- ----------
     90624          1          1 ID                            1          2          0
     90624          2          2 V1                            2          1          0
     90624          3          3 V2                            3          1          0

SCOTT@book> column spare6 format a20
SCOTT@book> select  OBJ#,DATAOBJ#,spare1,spare2,spare3,spare4,spare5,spare6 from sys.tab$  where obj#=90624;
      OBJ#   DATAOBJ#       SPARE1     SPARE2     SPARE3 SPARE4     SPARE5     SPARE6
---------- ---------- ------------ ---------- ---------- ---------- ---------- --------------------
     90624      90624          736                                             2017-11-13 06:59:26

SCOTT@book> ALTER TABLE t1 SET UNUSED (v1);
Table altered.

SCOTT@book> select  OBJ#,DATAOBJ#,spare1,spare2,spare3,spare4,spare5,spare6 from sys.tab$  where obj#=90624;
      OBJ#   DATAOBJ#       SPARE1     SPARE2     SPARE3 SPARE4     SPARE5     SPARE6
---------- ---------- ------------ ---------- ---------- ---------- ---------- --------------------
     90624      90624          736                                             2017-11-13 07:01:07

SCOTT@book>  SELECT obj#,col#, segcol#, name, intcol#, type#,PROPERTY FROM sys.col$ WHERE obj# IN (SELECT object_id FROM dba_objects WHERE object_name = 'T1' AND owner = user);
      OBJ#       COL#    SEGCOL# NAME                              INTCOL#      TYPE#   PROPERTY
---------- ---------- ---------- ------------------------------ ---------- ---------- ----------
     90624          1          1 ID                                      1          2          0
     90624          0          2 SYS_C00002_17111315:01:08$              2          1      32800
     90624          2          3 V2                                      3          1          0

--//你可以发现在ALTER TABLE t1 DROP UNUSED COLUMNS CHECKPOINT 10;前,sys.tab$的spare4为null.
--//session 1:

SCOTT@book> @ &r/spid
       SID    SERIAL# PROCESS                  SERVER    SPID       PID  P_SERIAL# C50
---------- ---------- ------------------------ --------- ------ ------- ---------- --------------------------------------------------
        54        203 49380                    DEDICATED 49381       28         74 alter system kill session '54,203' immediate;

--//确定转储文件: /u01/app/oracle/diag/rdbms/book/book/trace/book_ora_49381.trc

$ cat x1.sql
@ &r/10046on 12
select current_scn from v$database ;
ALTER TABLE t1 DROP UNUSED COLUMNS CHECKPOINT 10;
select current_scn from v$database ;
@ &r/10046off

SCOTT@book> select  OBJ#,DATAOBJ#,spare1,spare2,spare3,spare4,dump(spare4,16) c30,spare5,spare6 from sys.tab$  where obj#=90624;
      OBJ#   DATAOBJ#     SPARE1     SPARE2     SPARE3 SPARE4     C30                            SPARE5     SPARE6
---------- ---------- ---------- ---------- ---------- ---------- ------------------------------ ---------- --------------------
     90624      90624        736                        寠 k     Typ=1 Len=6: 1,0,8c,8a,0,6b               2017-11-13 07:01:07

--// 检查跟踪文件,发现如下:(注sql语句我做了格式化处理.)
PARSING IN CURSOR #140630994050912 len=532 dep=1 uid=0 oct=6 lid=0 tim=1510556663952810 hv=685354830 ad='7bc57128' sqlid='b5cr4hhndmbuf'
UPDATE tab$
   SET ts#  = :2,
       file# = :3,
       block# = :4,
       bobj# = decode(:5,
       0,
       null,
       :5),
       tab# = decode(:6,
       0,
       null,
       :6),
       intcols = :7,
       kernelcols = :8,
       clucols = decode(:9,
       0,
       null,
       :9),
       audit$ = :10,
       flags = :11,
       pctfree$ = :12,
       pctused$ = :13,
       initrans = :14,
       maxtrans = :15,
       rowcnt = :16,
       blkcnt = :17,
       empcnt = :18,
       avgspc = :19,
       chncnt = :20,
       avgrln = :21,
       analyzetime = :22,
       samplesize = :23,
       cols = :24,
       property = :25,
       degree = decode(:26,
       1,
       null,
       :26),
       instances = decode(:27,
       1,
       null,
       :27),
       dataobj# = :28,
       avgspc_flb = :29,
       flbcnt = :30,
       trigflag = :31,
       spare1 = :32,
       spare2 = decode(:33,
       0,
       null,
       :33),
       spare4 = :34,
       spare6 = :35
 WHERE obj# = :1
END OF STMT

*** 2017-11-13 15:04:23.953
BINDS #140630995900744:
 Bind#0
  oacdty=02 mxl=22(22) mxlc=00 mal=00 scl=00 pre=00
  oacflg=00 fl2=0001 frm=00 csi=00 siz=48 off=0
  kxsbbbfp=7fe73485db08  bln=22  avl=02  flg=05
  value=4
 Bind#1
  oacdty=02 mxl=22(22) mxlc=00 mal=00 scl=00 pre=00
  oacflg=00 fl2=0001 frm=00 csi=00 siz=0 off=24
  kxsbbbfp=7fe73485db20  bln=22  avl=02  flg=01
  value=3
...

Bind#38
  oacdty=01 mxl=32(06) mxlc=00 mal=00 scl=00 pre=00
  oacflg=10 fl2=0001 frm=01 csi=852 siz=32 off=0
  kxsbbbfp=7c1eef40  bln=32  avl=06  flg=09
  value="^A"
~~~~~~~~~~~~~~~~~~  
 Bind#39
  oacdty=12 mxl=07(07) mxlc=00 mal=00 scl=00 pre=00
  oacflg=10 fl2=0001 frm=00 csi=00 siz=8 off=0
  kxsbbbfp=7c1eef5e  bln=07  avl=07  flg=09
  value="11/13/2017 7:1:7"
 Bind#40
  oacdty=02 mxl=22(22) mxlc=00 mal=00 scl=00 pre=00
  oacflg=00 fl2=0001 frm=00 csi=00 siz=24 off=0
  kxsbbbfp=7fe734950188  bln=22  avl=04  flg=05
  value=90624

--//注意看下划线就是插入sprae4的值.

SCOTT@book> select  OBJ#,DATAOBJ#,spare1,spare2,spare3,spare4,dump(spare4,16) c30,spare5,spare6 from sys.tab$  where obj#=90624;
      OBJ#   DATAOBJ#     SPARE1     SPARE2     SPARE3 SPARE4     C30                            SPARE5     SPARE6
---------- ---------- ---------- ---------- ---------- ---------- ------------------------------ ---------- --------------------
     90624      90624        736                        寠 k     Typ=1 Len=6: 1,0,8c,8a,0,6b                2017-11-13 07:01:07

--//不知道spare4的插入值的具体含义.可以知道仅仅与drop 字段有关.转储日志分析看看:

alter system dump logfile '/mnt/ramdisk/book/redo02.log' scn min 13277923577 scn max 13277943577;

$ egrep "col 33: \[ 6\]  01 00|col  0: \[ 4\]  c3 0a 07 19" /u01/app/oracle/diag/rdbms/book/book/trace/book_ora_49641.trc > /tmp/aa.txt
--//注 c3 0a 07 18 对应的是obj#字段
SCOTT@book> select dump(90624,16) from dual ;
DUMP(90624,16)
----------------------
Typ=2 Len=4: c3,a,7,19

--//检查/tmp/aa.txt文本,可以发现如下信息.
col  0: [ 4]  c3 0a 07 19
col 33: [ 6]  01 00 7a cb 00 0a
col  0: [ 4]  c3 0a 07 19
col 33: [ 6]  01 00 7a cb 00 0a
col  0: [ 4]  c3 0a 07 19
col 33: [ 6]  01 00 7a cb 00 14
col  0: [ 4]  c3 0a 07 19
col 33: [ 6]  01 00 7a cb 00 14
col  0: [ 4]  c3 0a 07 19
col 33: [ 6]  01 00 7a cb 00 1e
col  0: [ 4]  c3 0a 07 19
col 33: [ 6]  01 00 7a cb 00 1e
col  0: [ 4]  c3 0a 07 19
col 33: [ 6]  01 00 7a cb 00 28
col  0: [ 4]  c3 0a 07 19
col 33: [ 6]  01 00 7a cb 00 28
col  0: [ 4]  c3 0a 07 19
...

--//0x0a=10,0x14=20,1e=30,0x28=40.哈哈看出来了吗?这个就是每次提交的记录行号. 我是每10条一个提交,这样就很好猜测rowid之类的信息.
--//spare4记录下一条操作的记录rowid,我估计.
--//如果继续往下看

col  0: [ 4]  c3 0a 07 19
col 33: [ 6]  01 00 7a cb 01 0e
col  0: [ 4]  c3 0a 07 19
col 33: [ 6]  01 00 7a cc 00 01
col  0: [ 4]  c3 0a 07 19

--//这里跨块了,0x10e=270.
--//好了修复看看该表的rowid一切就清楚了.

SCOTT@book> ALTER TABLE t1 DROP COLUMNS CONTINUE;
Table altered.

SCOTT@book> select  OBJ#,DATAOBJ#,spare1,spare2,spare3,spare4,dump(spare4,16) c30,spare5,spare6 from sys.tab$  where obj#=90624;
        OBJ#     DATAOBJ#     SPARE1     SPARE2     SPARE3 SPARE4     C30                            SPARE5     SPARE6
------------ ------------ ---------- ---------- ---------- ---------- ------------------------------ ---------- --------------------
       90624        90624        736                                  NULL                                      2017-11-13 07:54:14
--//完成后spare4内容清空.

SCOTT@book> select rowid,t1.* from t1 where rownum<=2;
ROWID                        ID V2
------------------ ------------ ----------
AAAWIAAAEAAAHrLAAA          563 bbbbbbbbbb
AAAWIAAAEAAAHrLAAB          564 bbbbbbbbbb

SCOTT@book> @ &r/rowid AAAWIAAAEAAAHrLAAA
      OBJECT         FILE        BLOCK          ROW ROWID_DBA            DBA                  TEXT
------------ ------------ ------------ ------------ -------------------- -------------------- ----------------------------------------
       90624            4        31435            0  0x1007ACB           4,31435              alter system dump datafile 4 block 31435

--//注意看ROWID_DBA,就是块地址.与前面的转储内容一直.可以猜测这块279条记录.因为下一个记录是"01 00 7a cc 00 01".
--//块dba=0x01007acc有1条已经提交了+加上剩下9条作为一个事务提交.验证看看.

SCOTT@book> select count(*) from t1 where rowid between 'AAAWIAAAEAAAHrLAAA' and 'AAAWIAAAEAAAHrLBBB';
    COUNT(*)
------------
         279

--//继续看下面也验证了猜测.
col  0: [ 4]  c3 0a 07 19
col 33: [ 6]  01 00 7a cc 01 0f
col  0: [ 4]  c3 0a 07 19
col 33: [ 6]  01 00 7a cd 00 02
col  0: [ 4]  c3 0a 07 19

总结:
1.ALTER TABLE <table_name> DROP UNUSED COLUMNS CHECKPOINT <n>;
In the ALTER TABLE statement that follows, the optional clause CHECKPOINT is specified. This clause causes a checkpoint
to be applied after processing the specified number of rows, in this case 250. Checkpointing cuts down on the amount of
undo logs accumulated during the drop column operation to avoid a potential exhaustion of undo space.

--//虽然减少undo的使用,但是如果中断或者中途退出,表无法查询与使用,必须执行ALTER TABLE <table_name> DROP COLUMNS CONTINUE;修复.
--//并且再使用checkpoint 参数.

--//oracle是通过修改相应sys.tab$表的spare4的值来确定这个工作是否完成,并且这里记录的是下一次要操作记录的rowid.

2.测试很幸运正好sys.tab$显示pare4线索异常, 最佳的方式应该是直接跟踪ALTER TABLE t1 DROP UNUSED COLUMNS CHECKPOINT 10;操作.走了一个弯路.^_^.