[20200814]8K数据库最大行号.txt

[20200814]8K数据库最大行号.txt

--//昨天听别人上课,对方想演示ITL槽不足出现的阻塞和死锁情况,讲到oracle 8K的数据块最大行号不能超过736.实际上
--//比较准确的提法是1块(数据块大小8k)最多仅仅容纳736条记录,实测733.估计采用mssm模式可以达到736条(注:我没测试).

--//我记忆里我以前做过一个例子演示行号可以超过这个限制,找了一下以前的测试,在12c上重复演示看看.
--//原始链接:http://blog.itpub.net/267265/viewspace-746749/=>[20121019]8k数据块到底能放多少行记录.txt

1.环境:
SCOTT@test01p> @ ver1

PORT_STRING                    VERSION        BANNER                                                                               CON_ID
------------------------------ -------------- -------------------------------------------------------------------------------- ----------
IBMPC/WIN_NT64-9.1.0           12.2.0.1.0     Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production              0

2.建立测试脚本:

drop table t2 purge ;

SCOTT@test01p> create table t2 (a number) pctfree 0;
Table created.

SELECT tab.spare1, obj.object_id, obj.data_object_id, obj.object_name
  FROM SYS.tab$ tab, dba_objects obj
 WHERE tab.obj# = obj.object_id AND tab.dataobj# = obj.data_object_id AND obj.owner = USER AND obj.object_name = 'T2';

 SPARE1  OBJECT_ID DATA_OBJECT_ID OBJECT_NAME
------- ---------- -------------- --------------------
    736      28720          28720 T2
--// SPARE1=736.

declare
 v_newrowid rowid;
begin
 for i in 1..4000 loop
   insert into t2 values(null) returning rowid into v_newrowid;
   delete from t2 where rowid=v_newrowid;
 end loop;
 insert into t2 values(NULL);
 commit;
end;
/

--//在一个事务里面,插入1条记录占用1个行目录,再删除记录后,由于在一个事务里面,不会重用原来的行目录,这样最终可以确定最大的
--//行号.为了确定表T2占用的块地址,插入1条记录并提交.

3.测试:
--//执行以上脚本后:
SCOTT@test01p> alter system checkpoint ;
System altered.

SCOTT@test01p> select rowid,t2.* from t2;
ROWID                       A
------------------ ----------
AAAHAwAALAAAAE2AfB

SCOTT@test01p> @ rowid AAAHAwAALAAAAE2AfB
    OBJECT       FILE      BLOCK        ROW ROWID_DBA            DBA                  TEXT
---------- ---------- ---------- ---------- -------------------- -------------------- ----------------------------------------
     28720         11        310       1985  0x2C00136           11,310               alter system dump datafile 11 block 310
--//可以发现行号=1985.

SCOTT@test01p> alter table t2 minimize records_per_block;
Table altered.

SELECT tab.spare1, obj.object_id, obj.data_object_id, obj.object_name
  FROM SYS.tab$ tab, dba_objects obj
 WHERE tab.obj# = obj.object_id AND tab.dataobj# = obj.data_object_id AND obj.owner = USER AND obj.object_name = 'T2';

 SPARE1  OBJECT_ID DATA_OBJECT_ID OBJECT_NAME
------- ---------- -------------- -----------------
  34753      28720          28720 T2
--// SPARE1=34753.
--// 34753-32768=1985,难道12c最大行号1985.具体看后面分析...
--//在这样的情况下建立位图索引,不会存在问题.
SCOTT@test01p> create bitmap index i_t2_a on t2(a);
Index created.

SCOTT@test01p> drop index i_t2_a ;
Index dropped.

--//通过bbed观察,注意bbed for windows查看时block要+1,主要原因是bbed for windows版本对应是9i的,无法识别12c的数据文件的
--//OS头,后面的测试数据块都要+1,不再另外说明.

BBED> map dba 11,311
 File: D:\APP\ORACLE\ORADATA\TEST\TEST01P\USERS01.DBF (11)
 Block: 311                                   Dba:0x02c00137
------------------------------------------------------------
 KTB Data Block (Table/Cluster)
 struct kcbh, 20 bytes                      @0
 struct ktbbh, 72 bytes                     @20
 struct kdbh, 14 bytes                      @100
 struct kdbt[1], 4 bytes                    @114
 sb2 kdbr[1986]                             @118
 ub1 freespace[75]                          @4090
 ub1 rowdata[4023]                          @4165
 ub4 tailchk                                @8188
--//sb2 kdbr[1986] ,也就是最大行号1985(从0开始计算).如果取消minimize records_per_block设置.

SQL> alter table t2 nominimize records_per_block;
Table altered.

SELECT tab.spare1, obj.object_id, obj.data_object_id, obj.object_name
  FROM SYS.tab$ tab, dba_objects obj
 WHERE tab.obj# = obj.object_id AND tab.dataobj# = obj.data_object_id AND obj.owner = USER AND obj.object_name = 'T2';

 SPARE1  OBJECT_ID DATA_OBJECT_ID OBJECT_NAME
------- ---------- -------------- --------------------
    736      28720          28720 T2
--//spare1=736.还原.再次建立位图索引看看.

SCOTT@test01p> create bitmap index i_t2_a on t2(a);
create bitmap index i_t2_a on t2(a)
                              *
ERROR at line 1:
ORA-28604: table too fragmented to build bitmap index (46137654,1985,744)

d:\>oerr ora 28604
28604, 00000, "table too fragmented to build bitmap index (%s,%s,%s)"
// *Cause:  The table has one or more blocks that exceed the maximum number
//          of rows expected when creating a bitmap index. This is probably
//          due to deleted rows. The values in the message are:
//          (data block address, slot number found, maximum slot allowed)
// *Action: Defragment the table or block(s). Use the values in the message
//          to determine the FIRST block affected. (There may be others).

--//翻译: 该表有一个或多个块，超过创建位图索引时预期的最大行数。 这可能是由于删除了行。
--//      消息中的值是： (数据块地址、找到的插槽号、允许的最大插槽)
--//46137654 = set dba 11,310 = alter system dump datefile 11 block 310 = 0x2c00136,对应块地址.
--//第1,2个参数都能对上.而第3个参数是允许的最大插槽744,有点奇怪比736大8.

4.继续:
--//仔细看了原始链接,发现我现在改写的脚本有一点点问题,难道执行4000次循环.接着
--//插入的行目录在1985.minimize records_per_block具有回收行目录的功能吗? 我记忆当时测试最大2015,
--//但是以后重复测试无论如何最大2014.重复测试:

drop table t2 purge ;
create table t2 (a number) pctfree 0;

declare
 v_newrowid rowid;
begin
 for i in 1..4000 loop
   insert into t2 values(null) returning rowid into v_newrowid;
   delete from t2 where rowid=v_newrowid;
 end loop;
end;
/

insert into t2 values(NULL);
commit ;
insert into t2 values(NULL);
rollback;
--//注:这里有点误操作...手快了....

alter system checkpoint ;

SCOTT@test01p> select rowid,t2.* from t2;
ROWID                       A
------------------ ----------
AAAHA7AALAAAAE2AfB

SCOTT@test01p> @ rowid AAAHA7AALAAAAE2AfB
    OBJECT       FILE      BLOCK        ROW ROWID_DBA            DBA                  TEXT
---------- ---------- ---------- ---------- -------------------- -------------------- ----------------------------------------
     28731         11        310       1985  0x2C00136           11,310               alter system dump datafile 11 block 310
--//注:我当前会话没有退出,应该还是插入在dba=11,310的位置.

BBED> map dba 11,311
 File: D:\APP\ORACLE\ORADATA\TEST\TEST01P\USERS01.DBF (11)
 Block: 311                                   Dba:0x02c00137
------------------------------------------------------------
 KTB Data Block (Table/Cluster)
 struct kcbh, 20 bytes                      @0
 struct ktbbh, 72 bytes                     @20
 struct kdbh, 14 bytes                      @100
 struct kdbt[1], 4 bytes                    @114
 sb2 kdbr[1987]                             @118
 ub1 freespace[70]                          @4092
 ub1 rowdata[4026]                          @4162
 ub4 tailchk                                @8188
--// sb2 kdbr[1987]  @118,说明我当前的行号还可以增加,这样解析不通.这样前面4000-1985 = 2015,无法解析得通.

BBED> map dba 11,310
 File: D:\APP\ORACLE\ORADATA\TEST\TEST01P\USERS01.DBF (11)
 Block: 310                                   Dba:0x02c00136
------------------------------------------------------------
 KTB Data Block (Table/Cluster)
 struct kcbh, 20 bytes                      @0
 struct ktbbh, 72 bytes                     @20
 struct kdbh, 14 bytes                      @100
 struct kdbt[1], 4 bytes                    @114
 sb2 kdbr[2015]                             @118
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 ub1 freespace[7]                           @4148
 ub1 rowdata[4033]                          @4155
 ub4 tailchk                                @8188
--//噢!注意看下划线,实际上在另外的块行号已经到2015,对于这个回话相当于该块满了,只能选择新的一块继续DML的执行.
--//这样可以解析先在dba=11,309插入2015条再删除.再在dba=11,310插入1985条.

--//但是还是我无法解析为什么链接http://blog.itpub.net/267265/viewspace-746749/,测试时看到最大2014.
declare
 v_newrowid rowid;
begin
 for i in 1..20000 loop
  if i=2000 then
   insert into t2 values(NULL);
  else
   insert into t2 values(null) returning rowid into v_newrowid;
   delete from t2 where rowid=v_newrowid;
  end if;
 end loop;
end;
/
--//注以上脚本是我当时执行的脚本.继续观察当前的测试:

BBED> set dba 11,310
BBED> p kdbr
BBED> p kdbr
sb2 kdbr[0]                                 @118      8086
sb2 kdbr[1]                                 @120      8084
sb2 kdbr[2]                                 @122      8082
sb2 kdbr[3]                                 @124      8080
sb2 kdbr[4]                                 @126      8078
...
sb2 kdbr[2006]                              @4130     4074
sb2 kdbr[2007]                              @4132     4072
sb2 kdbr[2008]                              @4134     4070
sb2 kdbr[2009]                              @4136     4068
sb2 kdbr[2010]                              @4138     4066
sb2 kdbr[2011]                              @4140     4064
sb2 kdbr[2012]                              @4142     4061
sb2 kdbr[2013]                              @4144     4058
sb2 kdbr[2014]                              @4146     4055
--//发现1点点奇怪之处,前面的偏移开始相差2,而后面3个相差3.看看dba=11,310的情况:

BBED> p dba 11,311 kdbr
sb2 kdbr[0]                                 @118      8086
sb2 kdbr[1]                                 @120      8084
sb2 kdbr[2]                                 @122      8082
sb2 kdbr[3]                                 @124      8080
sb2 kdbr[4]                                 @126      8078
...
sb2 kdbr[1933]                              @3984     4220
sb2 kdbr[1934]                              @3986     4218
--//开始相差3.
sb2 kdbr[1935]                              @3988     4215
sb2 kdbr[1936]                              @3990     4212
sb2 kdbr[1937]                              @3992     4209
sb2 kdbr[1938]                              @3994     4206
sb2 kdbr[1939]                              @3996     4203

sb2 kdbr[1940]                              @3998     4200
sb2 kdbr[1941]                              @4000     4197
sb2 kdbr[1942]                              @4002     4194
sb2 kdbr[1943]                              @4004     4191
sb2 kdbr[1944]                              @4006     4188
sb2 kdbr[1945]                              @4008     4185
sb2 kdbr[1946]                              @4010     4182
sb2 kdbr[1947]                              @4012     4179
sb2 kdbr[1948]                              @4014     4176
sb2 kdbr[1949]                              @4016     4173
sb2 kdbr[1950]                              @4018     4170
sb2 kdbr[1951]                              @4020     4167
sb2 kdbr[1952]                              @4022     4164
sb2 kdbr[1953]                              @4024     4161
sb2 kdbr[1954]                              @4026     4158
sb2 kdbr[1955]                              @4028     4155
sb2 kdbr[1956]                              @4030     4152
sb2 kdbr[1957]                              @4032     4149
sb2 kdbr[1958]                              @4034     4146
sb2 kdbr[1959]                              @4036     4143
sb2 kdbr[1960]                              @4038     4140
sb2 kdbr[1961]                              @4040     4137
sb2 kdbr[1962]                              @4042     4134
sb2 kdbr[1963]                              @4044     4131
sb2 kdbr[1964]                              @4046     4128
sb2 kdbr[1965]                              @4048     4125
sb2 kdbr[1966]                              @4050     4122
sb2 kdbr[1967]                              @4052     4119
sb2 kdbr[1968]                              @4054     4116
sb2 kdbr[1969]                              @4056     4113
sb2 kdbr[1970]                              @4058     4110
sb2 kdbr[1971]                              @4060     4107
sb2 kdbr[1972]                              @4062     4104
sb2 kdbr[1973]                              @4064     4101
sb2 kdbr[1974]                              @4066     4098
sb2 kdbr[1975]                              @4068     4095
sb2 kdbr[1976]                              @4070     4092
sb2 kdbr[1977]                              @4072     4089
sb2 kdbr[1978]                              @4074     4086
sb2 kdbr[1979]                              @4076     4083
sb2 kdbr[1980]                              @4078     4080
sb2 kdbr[1981]                              @4080     4077
sb2 kdbr[1982]                              @4082     4074
sb2 kdbr[1983]                              @4084     4071
sb2 kdbr[1984]                              @4086     4068
sb2 kdbr[1985]                              @4088     4065
sb2 kdbr[1986]                              @4090    -1
--//可以确定oracle在dml时做了块内重整.修改了行目录的偏移量.这样可以容纳更多的行号.
--//也就是如果循环插入NULL再删除,这样在pctrfee=0的情况下看到的最大行号是2015.

5.看看minimize records_per_block后情况,是否会修改kdbr行目录数量.
SCOTT@test01p> alter table t2 minimize records_per_block;
Table altered.

SCOTT@test01p> alter system checkpoint ;
System altered.

SELECT tab.spare1, obj.object_id, obj.data_object_id, obj.object_name
  FROM SYS.tab$ tab, dba_objects obj
 WHERE tab.obj# = obj.object_id AND tab.dataobj# = obj.data_object_id AND obj.owner = USER AND obj.object_name = 'T2';

 SPARE1  OBJECT_ID DATA_OBJECT_ID OBJECT_NAME
------- ---------- -------------- -----------
  34753      28731          28731 T2

--//34753-32767=1986.

BBED> map dba 11,310
 File: D:\APP\ORACLE\ORADATA\TEST\TEST01P\USERS01.DBF (11)
 Block: 310                                   Dba:0x02c00136
------------------------------------------------------------
 KTB Data Block (Table/Cluster)
 struct kcbh, 20 bytes                      @0
 struct ktbbh, 72 bytes                     @20
 struct kdbh, 14 bytes                      @100
 struct kdbt[1], 4 bytes                    @114
 sb2 kdbr[2015]                             @118
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 ub1 freespace[7]                           @4148
 ub1 rowdata[4033]                          @4155
 ub4 tailchk                                @8188
--//并不会改变行目录数量.

BBED> map dba 11,311
 File: D:\APP\ORACLE\ORADATA\TEST\TEST01P\USERS01.DBF (11)
 Block: 311                                   Dba:0x02c00137
------------------------------------------------------------
 KTB Data Block (Table/Cluster)
 struct kcbh, 20 bytes                      @0
 struct ktbbh, 72 bytes                     @20
 struct kdbh, 14 bytes                      @100
 struct kdbt[1], 4 bytes                    @114
 sb2 kdbr[1987]                             @118
 ub1 freespace[70]                          @4092
 ub1 rowdata[4026]                          @4162
 ub4 tailchk                                @8188
--//有点乱...

总结:
--//1.这种情况在实际的生产环境很难遇到.
--//2.从前面建立位图索引时遇到ORA-28604,提示第3个参数是744,是否意味着oracle留有一定的余地.行号在736-744之间时建立位图索
--//引一样建立成功.补充测试看看.

ORA-28604: table too fragmented to build bitmap index (46137654,1985,744)

d:\>oerr ora 28604
28604, 00000, "table too fragmented to build bitmap index (%s,%s,%s)"
// *Cause:  The table has one or more blocks that exceed the maximum number
//          of rows expected when creating a bitmap index. This is probably
//          due to deleted rows. The values in the message are:
//          (data block address, slot number found, maximum slot allowed)
// *Action: Defragment the table or block(s). Use the values in the message
//          to determine the FIRST block affected. (There may be others).

drop table t2 purge ;
create table t2 (a number) pctfree 0;

SELECT tab.spare1, obj.object_id, obj.data_object_id, obj.object_name
  FROM SYS.tab$ tab, dba_objects obj
 WHERE tab.obj# = obj.object_id AND tab.dataobj# = obj.data_object_id AND obj.owner = USER AND obj.object_name = 'T2';

 SPARE1  OBJECT_ID DATA_OBJECT_ID OBJECT_NAME
------- ---------- -------------- --------------------
    736      28740          28740 T2
--//SPARE1=736.

declare
 v_newrowid rowid;
begin
 for i in 1..743 loop
   insert into t2 values(null) returning rowid into v_newrowid;
   delete from t2 where rowid=v_newrowid;
 end loop;
 insert into t2 values(NULL);
 commit;
end;
/

SCOTT@test01p> select rowid,t2.* from t2;
ROWID                       A
------------------ ----------
AAAHBEAALAAAAE1ALn

SCOTT@test01p> @ rowid AAAHBEAALAAAAE1ALn
    OBJECT       FILE      BLOCK        ROW ROWID_DBA            DBA                  TEXT
---------- ---------- ---------- ---------- -------------------- -------------------- ----------------------------------------
     28740         11        309        743  0x2C00135           11,309               alter system dump datafile 11 block 309

SCOTT@test01p> create bitmap index i_t2_a on t2(a);
Index created.

--//位图索引建立成功,而实际上行号=743.

SCOTT@test01p> alter table t2 minimize records_per_block;
alter table t2 minimize records_per_block
*
ERROR at line 1:
ORA-28602: statement not permitted on tables containing bitmap indexes

SCOTT@test01p> drop index i_t2_a;
Index dropped.

SCOTT@test01p> alter table t2 minimize records_per_block;
Table altered.

SELECT tab.spare1, obj.object_id, obj.data_object_id, obj.object_name
  FROM SYS.tab$ tab, dba_objects obj
 WHERE tab.obj# = obj.object_id AND tab.dataobj# = obj.data_object_id AND obj.owner = USER AND obj.object_name = 'T2';

 SPARE1  OBJECT_ID DATA_OBJECT_ID OBJECT_NAME
------- ---------- -------------- --------------------
  33511      28740          28740 T2
--//33511-32767 = 744.

--//如果建立表后执行如下,就无法建立位图索引.

declare
 v_newrowid rowid;
begin
 for i in 1..744 loop
   insert into t2 values(null) returning rowid into v_newrowid;
   delete from t2 where rowid=v_newrowid;
 end loop;
 insert into t2 values(NULL);
 commit;
end;
/

--//留给大家测试,我不做了.^_^.