写入值顺序和乱序对数据访问的影响
数据写入到表时， 写入值顺序和乱序对数据访问的影响
2017-12-13 听了高斌的讲解， 自己做了实验，验证了下面的结论：
当普通 heap表，即堆表， 在写入值时，被索引值的写入顺序会影响访问性能 ：
1. 当写入值是顺序的时候， 表记录也是在 block 里按照顺序写入， 即 id = 1，2，3，4，5 记录 会写入 第一个 block ，当第一个block写满后 ，
顺序写入下一个block， 这个顺序指的是磁盘访问顺序 。
2. 当写入值是乱序时， 乱序表记录就会存放在顺序的block里面， 差别很大的 id 值的 几条记录放在同一个块里面 。
3. 当 使用索引的时候， 被索引的值是根据 B* 树来进行从小到大排序的，
上述 情况 1的时候， 多个索引块指向 一个数据块 ，
上述情况2 的时候， 一个索引块里面的值 指向 多个 表 数据块
4. 分区以后， 打破 数据块 热点
5. reverse 键值后 打破了索引热块
drop table testseq ;
drop table testsca ;
create table testseq ( id number(18) , fname varchar(1000) ) ;
create index ind_seq on testseq(id) ;
create table testsca ( id number(18) , fname varchar(1000) ) ;
create index ind_sca on testsca(id) ;
---- 写入1 万行数据，
SQL> select * from v$version ;
BANNER
------------------------------------------------------------------------------
Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production
PL/SQL Release 12.2.0.1.0 - Production
CORE 12.2.0.1.0 Production
TNS for 64-bit Windows: Version 12.2.0.1.0 - Production
NLSRTL Version 12.2.0.1.0 - Production
SQL> select extent_id , bytes, blocks from user_extents where segment_name='TESTSEQ' ;
no rows selected
SQL> select extent_id , bytes , blocks from user_extents where segment_name='TESTSCA' ;
no rows selected
SQL>
begin
for i in 1..10000 loop
insert into testseq ( id , fname ) values ( i , dbms_random.String('a', 1000 ) ) ;
end loop ;
commit;
end;
/
Elapsed: 00:00:44.70
begin
for i in 1..10000 loop
insert into testsca ( id , fname ) values ( dbms_random.value(1, 10000 ) , dbms_random.String('a', 1000 ) ) ;
end loop ;
commit;
end;
/
Elapsed: 00:00:45.82
select extent_id , bytes, blocks from user_extents where segment_name='TESTSEQ' ;
EXTENT_ID BYTES BLOCKS
---------- ---------- ----------
0 65536 8
1 65536 8
2 65536 8
3 65536 8
4 65536 8
5 65536 8
6 65536 8
7 65536 8
8 65536 8
9 65536 8
10 65536 8
EXTENT_ID BYTES BLOCKS
---------- ---------- ----------
11 65536 8
12 65536 8
13 65536 8
14 65536 8
15 65536 8
16 1048576 128
17 1048576 128
18 1048576 128
19 1048576 128
20 1048576 128
21 1048576 128
EXTENT_ID BYTES BLOCKS
---------- ---------- ----------
22 1048576 128
23 1048576 128
24 1048576 128
25 1048576 128
26 1048576 128
27 rows selected.
select sum(blocks) from user_extents where segment_name='TESTSEQ' ;
SUM(BLOCKS)
-----------
1536
exec dbms_stats.gather_table_stats(user,'TESTSEQ');
analyze table TESTSEQ compute statistics;
select num_rows, blocks, empty_blocks, avg_row_len from user_tables where table_name = 'TESTSEQ' ;
NUM_ROWS BLOCKS EMPTY_BLOCKS AVG_ROW_LEN
---------- ---------- ------------ -----------
10000 1504 32 1010
一共 1536 block 分配给表, 32 是空的 1504 是使用的 ,
1504 + 32 = 1536
select id, rowid from testseq where rownum < 50 order by id ;
select id, substr(rowid,10,6) blocknumber , substr(rowid,16,3) rownumber from testseq where rownum < 100 order by id ;
ID BLOCKNUMBE ROWNUMBER
---------- ---------- ----------
1 AAAc7u AAA
2 AAAc7u AAB
3 AAAc7u AAC
4 AAAc7u AAD
5 AAAc7u AAE
6 AAAc7u AAF
7 AAAc7u AAG
8 AAAc7v AAA
9 AAAc7v AAB
10 AAAc7v AAC
11 AAAc7v AAD
ID BLOCKNUMBE ROWNUMBER
---------- ---------- ----------
12 AAAc7v AAE
13 AAAc7v AAF
14 AAAc7v AAG
15 AAAc7r AAA
16 AAAc7r AAB
17 AAAc7r AAC
18 AAAc7r AAD
19 AAAc7r AAE
20 AAAc7r AAF
21 AAAc7r AAG
22 AAAc7s AAA
ID BLOCKNUMBE ROWNUMBER
---------- ---------- ----------
23 AAAc7s AAB
24 AAAc7s AAC
25 AAAc7s AAD
26 AAAc7s AAE
27 AAAc7s AAF
28 AAAc7s AAG
29 AAAc7t AAA
30 AAAc7t AAB
31 AAAc7t AAC
32 AAAc7t AAD
33 AAAc7t AAE
ID BLOCKNUMBE ROWNUMBER
---------- ---------- ----------
34 AAAc7t AAF
35 AAAc7t AAG
36 AAAc74 AAA
37 AAAc74 AAB
38 AAAc74 AAC
39 AAAc74 AAD
40 AAAc74 AAE
41 AAAc74 AAF
42 AAAc74 AAG
43 AAAc76 AAA
44 AAAc76 AAB
ID BLOCKNUMBE ROWNUMBER
---------- ---------- ----------
45 AAAc76 AAC
46 AAAc76 AAD
47 AAAc76 AAE
48 AAAc76 AAF
49 AAAc76 AAG
50 AAAc77 AAA
51 AAAc77 AAB
52 AAAc77 AAC
53 AAAc77 AAD
54 AAAc77 AAE
55 AAAc77 AAF
ID BLOCKNUMBE ROWNUMBER
---------- ---------- ----------
56 AAAc77 AAG
57 AAAc78 AAA
58 AAAc78 AAB
59 AAAc78 AAC
60 AAAc78 AAD
61 AAAc78 AAE
62 AAAc78 AAF
63 AAAc78 AAG
64 AAAc79 AAA
65 AAAc79 AAB
66 AAAc79 AAC
ID BLOCKNUMBE ROWNUMBER
---------- ---------- ----------
67 AAAc79 AAD
68 AAAc79 AAE
69 AAAc79 AAF
70 AAAc79 AAG
71 AAAc7+ AAA
72 AAAc7+ AAB
73 AAAc7+ AAC
74 AAAc7+ AAD
75 AAAc7+ AAE
76 AAAc7+ AAF
77 AAAc7+ AAG
ID BLOCKNUMBE ROWNUMBER
---------- ---------- ----------
78 AAAc7/ AAA
79 AAAc7/ AAB
80 AAAc7/ AAC
81 AAAc7/ AAD
82 AAAc7/ AAE
83 AAAc7/ AAF
84 AAAc7/ AAG
85 AAAc75 AAA
86 AAAc75 AAB
87 AAAc75 AAC
88 AAAc75 AAD
ID BLOCKNUMBE ROWNUMBER
---------- ---------- ----------
89 AAAc75 AAE
90 AAAc75 AAF
91 AAAc75 AAG
92 AAAdoC AAA
134 AAAdoB AAA
135 AAAdoB AAB
136 AAAdoB AAC
137 AAAdoB AAD
138 AAAdoB AAE
139 AAAdoB AAF
140 AAAdoB AAG
select distinct blocknumber from ( select id, substr(rowid,10,6) blocknumber , substr(rowid,16,3) rownumber from testseq where rownum < 100 order by id ) ;
顺序写入的数据基本按照顺序在一个数据块里面， 当根据id的范围来选择数据时， 例如 id > 1 and id < 100 , 要读 15 个块
BLOCKNUMBE
----------
AAAc7s
AAAc7r
AAAc76
AAAc74
AAAc75
AAAdoB
AAAc7u
AAAc7v
AAAc78
AAAc7+
AAAdoC
BLOCKNUMBE
----------
AAAc77
AAAc7/
AAAc7t
AAAc79
15 rows selected.
select extent_id , bytes , blocks from user_extents where segment_name='TESTSCA' ;
EXTENT_ID BYTES BLOCKS
---------- ---------- ----------
0 65536 8
1 65536 8
2 65536 8
3 65536 8
4 65536 8
5 65536 8
6 65536 8
7 65536 8
8 65536 8
9 65536 8
10 65536 8
EXTENT_ID BYTES BLOCKS
---------- ---------- ----------
11 65536 8
12 65536 8
13 65536 8
14 65536 8
15 65536 8
16 1048576 128
17 1048576 128
18 1048576 128
19 1048576 128
20 1048576 128
21 1048576 128
EXTENT_ID BYTES BLOCKS
---------- ---------- ----------
22 1048576 128
23 1048576 128
24 1048576 128
25 1048576 128
26 1048576 128
27 rows selected.
select sum(blocks) from user_extents where segment_name='TESTSCA' ;
SUM(BLOCKS)
-----------
1536
exec dbms_stats.gather_table_stats(user,'TESTSCA');
analyze table TESTSCA compute statistics;
select num_rows, blocks, empty_blocks, avg_row_len from user_tables where table_name = 'TESTSCA' ;
NUM_ROWS BLOCKS EMPTY_BLOCKS AVG_ROW_LEN
---------- ---------- ------------ -----------
10000 1504 32 1011
select id, rowid from testsca where rownum < 100 order by id ;
select id, substr(rowid,10,6) blocknumber , substr(rowid,16,3) rownumber from testsca where rownum < 100 order by id ;
ID BLOCKNUMBE ROWNUMBER
---------- ---------- ----------
90 AAAeC/ AAD
210 AAAeDK AAA
285 AAAeDP AAG
298 AAAeC7 AAA
657 AAAeC7 AAF
740 AAAeDJ AAA
871 AAAeDP AAA
882 AAAeDI AAB
1022 AAAeC8 AAE
1028 AAAeC+ AAG
1082 AAAeC/ AAG
ID BLOCKNUMBE ROWNUMBER
---------- ---------- ----------
1142 AAAeDO AAC
1589 AAAeC8 AAA
1745 AAAeC/ AAF
1774 AAAeC/ AAA
1886 AAAeC9 AAE
2130 AAAeDK AAF
2259 AAAeC8 AAD
2352 AAAeDJ AAD
2441 AAAeDI AAG
2615 AAAeDR AAC
2759 AAAeC7 AAD
ID BLOCKNUMBE ROWNUMBER
---------- ---------- ----------
2768 AAAeDM AAG
2832 AAAeC/ AAB
2975 AAAeDI AAA
3184 AAAeDK AAC
3195 AAAeDN AAA
3229 AAAeDR AAA
3311 AAAeC8 AAB
3430 AAAeDI AAE
3506 AAAeC8 AAF
3659 AAAeDP AAD
3831 AAAeC+ AAB
ID BLOCKNUMBE ROWNUMBER
---------- ---------- ----------
3879 AAAeC+ AAA
3980 AAAeDM AAA
4202 AAAeC/ AAE
4291 AAAeDO AAG
4372 AAAeDL AAD
4437 AAAeDJ AAG
4519 AAAeC7 AAB
4541 AAAeC8 AAC
4588 AAAeDN AAD
4674 AAAeDM AAB
4715 AAAeC7 AAG
ID BLOCKNUMBE ROWNUMBER
---------- ---------- ----------
4772 AAAeC+ AAE
4942 AAAeC8 AAG
5051 AAAeDN AAF
5054 AAAeDI AAC
5107 AAAeC/ AAC
5238 AAAeDO AAE
5289 AAAeC7 AAE
5318 AAAeDJ AAF
5447 AAAeDL AAE
5468 AAAeDO AAB
5477 AAAeC9 AAA
ID BLOCKNUMBE ROWNUMBER
---------- ---------- ----------
5514 AAAeDR AAE
5624 AAAeC9 AAG
5908 AAAeDK AAE
5934 AAAeDJ AAB
6318 AAAeC+ AAF
6371 AAAeDJ AAC
6510 AAAeDS AAA
6568 AAAeDN AAC
6668 AAAeDO AAF
6763 AAAeDP AAF
6845 AAAeDL AAF
ID BLOCKNUMBE ROWNUMBER
---------- ---------- ----------
6850 AAAeDL AAG
6937 AAAeDR AAF
7054 AAAeDL AAA
7127 AAAeDJ AAE
7256 AAAeC9 AAB
7303 AAAeDN AAB
7348 AAAeDP AAC
7455 AAAeDR AAD
7504 AAAeDM AAF
7574 AAAeC9 AAF
7751 AAAeDK AAG
ID BLOCKNUMBE ROWNUMBER
---------- ---------- ----------
7869 AAAeDI AAF
8018 AAAeDO AAD
8136 AAAeC9 AAD
8264 AAAeDK AAD
8433 AAAeDK AAB
8527 AAAeDN AAE
8559 AAAeC7 AAC
8559 AAAeC+ AAC
8586 AAAeDM AAD
8659 AAAeDO AAA
8729 AAAeC9 AAC
ID BLOCKNUMBE ROWNUMBER
---------- ---------- ----------
8812 AAAeDP AAE
8813 AAAeDR AAG
8841 AAAeDR AAB
8901 AAAeC+ AAD
8968 AAAeDL AAB
9108 AAAeDI AAD
9330 AAAeDP AAB
9396 AAAeDN AAG
9513 AAAeDM AAC
9702 AAAeDM AAE
9783 AAAeDL AAC
select distinct blocknumber from ( select id, substr(rowid,10,6) blocknumber , substr(rowid,16,3) rownumber from testsca where rownum < 100 order by id ) ;
BLOCKNUMBE
----------
AAAeC+
AAAeDR
AAAeC/
AAAeDK
AAAeDO
AAAeC8
AAAeDL
AAAeDP
AAAeDJ
AAAeC9
AAAeDI
BLOCKNUMBE
----------
AAAeDN
AAAeDS
AAAeC7
AAAeDM
15 rows selected.
同样写入 15 个块， 但是 访问时 被索引的值是分布在多个数据块里面进行排序。
2017-12-13 听了高斌的讲解， 自己做了实验，验证了下面的结论：
当普通 heap表，即堆表， 在写入值时，被索引值的写入顺序会影响访问性能 ：
1. 当写入值是顺序的时候， 表记录也是在 block 里按照顺序写入， 即 id = 1，2，3，4，5 记录 会写入 第一个 block ，当第一个block写满后 ，
顺序写入下一个block， 这个顺序指的是磁盘访问顺序 。
2. 当写入值是乱序时， 乱序表记录就会存放在顺序的block里面， 差别很大的 id 值的 几条记录放在同一个块里面 。
3. 当 使用索引的时候， 被索引的值是根据 B* 树来进行从小到大排序的，
上述 情况 1的时候， 多个索引块指向 一个数据块 ，
上述情况2 的时候， 一个索引块里面的值 指向 多个 表 数据块
4. 分区以后， 打破 数据块 热点
5. reverse 键值后 打破了索引热块
drop table testseq ;
drop table testsca ;
create table testseq ( id number(18) , fname varchar(1000) ) ;
create index ind_seq on testseq(id) ;
create table testsca ( id number(18) , fname varchar(1000) ) ;
create index ind_sca on testsca(id) ;
---- 写入1 万行数据，
SQL> select * from v$version ;
BANNER
------------------------------------------------------------------------------
Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production
PL/SQL Release 12.2.0.1.0 - Production
CORE 12.2.0.1.0 Production
TNS for 64-bit Windows: Version 12.2.0.1.0 - Production
NLSRTL Version 12.2.0.1.0 - Production
SQL> select extent_id , bytes, blocks from user_extents where segment_name='TESTSEQ' ;
no rows selected
SQL> select extent_id , bytes , blocks from user_extents where segment_name='TESTSCA' ;
no rows selected
SQL>
begin
for i in 1..10000 loop
insert into testseq ( id , fname ) values ( i , dbms_random.String('a', 1000 ) ) ;
end loop ;
commit;
end;
/
Elapsed: 00:00:44.70
begin
for i in 1..10000 loop
insert into testsca ( id , fname ) values ( dbms_random.value(1, 10000 ) , dbms_random.String('a', 1000 ) ) ;
end loop ;
commit;
end;
/
Elapsed: 00:00:45.82
select extent_id , bytes, blocks from user_extents where segment_name='TESTSEQ' ;
EXTENT_ID BYTES BLOCKS
---------- ---------- ----------
0 65536 8
1 65536 8
2 65536 8
3 65536 8
4 65536 8
5 65536 8
6 65536 8
7 65536 8
8 65536 8
9 65536 8
10 65536 8
EXTENT_ID BYTES BLOCKS
---------- ---------- ----------
11 65536 8
12 65536 8
13 65536 8
14 65536 8
15 65536 8
16 1048576 128
17 1048576 128
18 1048576 128
19 1048576 128
20 1048576 128
21 1048576 128
EXTENT_ID BYTES BLOCKS
---------- ---------- ----------
22 1048576 128
23 1048576 128
24 1048576 128
25 1048576 128
26 1048576 128
27 rows selected.
select sum(blocks) from user_extents where segment_name='TESTSEQ' ;
SUM(BLOCKS)
-----------
1536
exec dbms_stats.gather_table_stats(user,'TESTSEQ');
analyze table TESTSEQ compute statistics;
select num_rows, blocks, empty_blocks, avg_row_len from user_tables where table_name = 'TESTSEQ' ;
NUM_ROWS BLOCKS EMPTY_BLOCKS AVG_ROW_LEN
---------- ---------- ------------ -----------
10000 1504 32 1010
一共 1536 block 分配给表, 32 是空的 1504 是使用的 ,
1504 + 32 = 1536
select id, rowid from testseq where rownum < 50 order by id ;
select id, substr(rowid,10,6) blocknumber , substr(rowid,16,3) rownumber from testseq where rownum < 100 order by id ;
ID BLOCKNUMBE ROWNUMBER
---------- ---------- ----------
1 AAAc7u AAA
2 AAAc7u AAB
3 AAAc7u AAC
4 AAAc7u AAD
5 AAAc7u AAE
6 AAAc7u AAF
7 AAAc7u AAG
8 AAAc7v AAA
9 AAAc7v AAB
10 AAAc7v AAC
11 AAAc7v AAD
ID BLOCKNUMBE ROWNUMBER
---------- ---------- ----------
12 AAAc7v AAE
13 AAAc7v AAF
14 AAAc7v AAG
15 AAAc7r AAA
16 AAAc7r AAB
17 AAAc7r AAC
18 AAAc7r AAD
19 AAAc7r AAE
20 AAAc7r AAF
21 AAAc7r AAG
22 AAAc7s AAA
ID BLOCKNUMBE ROWNUMBER
---------- ---------- ----------
23 AAAc7s AAB
24 AAAc7s AAC
25 AAAc7s AAD
26 AAAc7s AAE
27 AAAc7s AAF
28 AAAc7s AAG
29 AAAc7t AAA
30 AAAc7t AAB
31 AAAc7t AAC
32 AAAc7t AAD
33 AAAc7t AAE
ID BLOCKNUMBE ROWNUMBER
---------- ---------- ----------
34 AAAc7t AAF
35 AAAc7t AAG
36 AAAc74 AAA
37 AAAc74 AAB
38 AAAc74 AAC
39 AAAc74 AAD
40 AAAc74 AAE
41 AAAc74 AAF
42 AAAc74 AAG
43 AAAc76 AAA
44 AAAc76 AAB
ID BLOCKNUMBE ROWNUMBER
---------- ---------- ----------
45 AAAc76 AAC
46 AAAc76 AAD
47 AAAc76 AAE
48 AAAc76 AAF
49 AAAc76 AAG
50 AAAc77 AAA
51 AAAc77 AAB
52 AAAc77 AAC
53 AAAc77 AAD
54 AAAc77 AAE
55 AAAc77 AAF
ID BLOCKNUMBE ROWNUMBER
---------- ---------- ----------
56 AAAc77 AAG
57 AAAc78 AAA
58 AAAc78 AAB
59 AAAc78 AAC
60 AAAc78 AAD
61 AAAc78 AAE
62 AAAc78 AAF
63 AAAc78 AAG
64 AAAc79 AAA
65 AAAc79 AAB
66 AAAc79 AAC
ID BLOCKNUMBE ROWNUMBER
---------- ---------- ----------
67 AAAc79 AAD
68 AAAc79 AAE
69 AAAc79 AAF
70 AAAc79 AAG
71 AAAc7+ AAA
72 AAAc7+ AAB
73 AAAc7+ AAC
74 AAAc7+ AAD
75 AAAc7+ AAE
76 AAAc7+ AAF
77 AAAc7+ AAG
ID BLOCKNUMBE ROWNUMBER
---------- ---------- ----------
78 AAAc7/ AAA
79 AAAc7/ AAB
80 AAAc7/ AAC
81 AAAc7/ AAD
82 AAAc7/ AAE
83 AAAc7/ AAF
84 AAAc7/ AAG
85 AAAc75 AAA
86 AAAc75 AAB
87 AAAc75 AAC
88 AAAc75 AAD
ID BLOCKNUMBE ROWNUMBER
---------- ---------- ----------
89 AAAc75 AAE
90 AAAc75 AAF
91 AAAc75 AAG
92 AAAdoC AAA
134 AAAdoB AAA
135 AAAdoB AAB
136 AAAdoB AAC
137 AAAdoB AAD
138 AAAdoB AAE
139 AAAdoB AAF
140 AAAdoB AAG
select distinct blocknumber from ( select id, substr(rowid,10,6) blocknumber , substr(rowid,16,3) rownumber from testseq where rownum < 100 order by id ) ;
顺序写入的数据基本按照顺序在一个数据块里面， 当根据id的范围来选择数据时， 例如 id > 1 and id < 100 , 要读 15 个块
BLOCKNUMBE
----------
AAAc7s
AAAc7r
AAAc76
AAAc74
AAAc75
AAAdoB
AAAc7u
AAAc7v
AAAc78
AAAc7+
AAAdoC
BLOCKNUMBE
----------
AAAc77
AAAc7/
AAAc7t
AAAc79
15 rows selected.
select extent_id , bytes , blocks from user_extents where segment_name='TESTSCA' ;
EXTENT_ID BYTES BLOCKS
---------- ---------- ----------
0 65536 8
1 65536 8
2 65536 8
3 65536 8
4 65536 8
5 65536 8
6 65536 8
7 65536 8
8 65536 8
9 65536 8
10 65536 8
EXTENT_ID BYTES BLOCKS
---------- ---------- ----------
11 65536 8
12 65536 8
13 65536 8
14 65536 8
15 65536 8
16 1048576 128
17 1048576 128
18 1048576 128
19 1048576 128
20 1048576 128
21 1048576 128
EXTENT_ID BYTES BLOCKS
---------- ---------- ----------
22 1048576 128
23 1048576 128
24 1048576 128
25 1048576 128
26 1048576 128
27 rows selected.
select sum(blocks) from user_extents where segment_name='TESTSCA' ;
SUM(BLOCKS)
-----------
1536
exec dbms_stats.gather_table_stats(user,'TESTSCA');
analyze table TESTSCA compute statistics;
select num_rows, blocks, empty_blocks, avg_row_len from user_tables where table_name = 'TESTSCA' ;
NUM_ROWS BLOCKS EMPTY_BLOCKS AVG_ROW_LEN
---------- ---------- ------------ -----------
10000 1504 32 1011
select id, rowid from testsca where rownum < 100 order by id ;
select id, substr(rowid,10,6) blocknumber , substr(rowid,16,3) rownumber from testsca where rownum < 100 order by id ;
ID BLOCKNUMBE ROWNUMBER
---------- ---------- ----------
90 AAAeC/ AAD
210 AAAeDK AAA
285 AAAeDP AAG
298 AAAeC7 AAA
657 AAAeC7 AAF
740 AAAeDJ AAA
871 AAAeDP AAA
882 AAAeDI AAB
1022 AAAeC8 AAE
1028 AAAeC+ AAG
1082 AAAeC/ AAG
ID BLOCKNUMBE ROWNUMBER
---------- ---------- ----------
1142 AAAeDO AAC
1589 AAAeC8 AAA
1745 AAAeC/ AAF
1774 AAAeC/ AAA
1886 AAAeC9 AAE
2130 AAAeDK AAF
2259 AAAeC8 AAD
2352 AAAeDJ AAD
2441 AAAeDI AAG
2615 AAAeDR AAC
2759 AAAeC7 AAD
ID BLOCKNUMBE ROWNUMBER
---------- ---------- ----------
2768 AAAeDM AAG
2832 AAAeC/ AAB
2975 AAAeDI AAA
3184 AAAeDK AAC
3195 AAAeDN AAA
3229 AAAeDR AAA
3311 AAAeC8 AAB
3430 AAAeDI AAE
3506 AAAeC8 AAF
3659 AAAeDP AAD
3831 AAAeC+ AAB
ID BLOCKNUMBE ROWNUMBER
---------- ---------- ----------
3879 AAAeC+ AAA
3980 AAAeDM AAA
4202 AAAeC/ AAE
4291 AAAeDO AAG
4372 AAAeDL AAD
4437 AAAeDJ AAG
4519 AAAeC7 AAB
4541 AAAeC8 AAC
4588 AAAeDN AAD
4674 AAAeDM AAB
4715 AAAeC7 AAG
ID BLOCKNUMBE ROWNUMBER
---------- ---------- ----------
4772 AAAeC+ AAE
4942 AAAeC8 AAG
5051 AAAeDN AAF
5054 AAAeDI AAC
5107 AAAeC/ AAC
5238 AAAeDO AAE
5289 AAAeC7 AAE
5318 AAAeDJ AAF
5447 AAAeDL AAE
5468 AAAeDO AAB
5477 AAAeC9 AAA
ID BLOCKNUMBE ROWNUMBER
---------- ---------- ----------
5514 AAAeDR AAE
5624 AAAeC9 AAG
5908 AAAeDK AAE
5934 AAAeDJ AAB
6318 AAAeC+ AAF
6371 AAAeDJ AAC
6510 AAAeDS AAA
6568 AAAeDN AAC
6668 AAAeDO AAF
6763 AAAeDP AAF
6845 AAAeDL AAF
ID BLOCKNUMBE ROWNUMBER
---------- ---------- ----------
6850 AAAeDL AAG
6937 AAAeDR AAF
7054 AAAeDL AAA
7127 AAAeDJ AAE
7256 AAAeC9 AAB
7303 AAAeDN AAB
7348 AAAeDP AAC
7455 AAAeDR AAD
7504 AAAeDM AAF
7574 AAAeC9 AAF
7751 AAAeDK AAG
ID BLOCKNUMBE ROWNUMBER
---------- ---------- ----------
7869 AAAeDI AAF
8018 AAAeDO AAD
8136 AAAeC9 AAD
8264 AAAeDK AAD
8433 AAAeDK AAB
8527 AAAeDN AAE
8559 AAAeC7 AAC
8559 AAAeC+ AAC
8586 AAAeDM AAD
8659 AAAeDO AAA
8729 AAAeC9 AAC
ID BLOCKNUMBE ROWNUMBER
---------- ---------- ----------
8812 AAAeDP AAE
8813 AAAeDR AAG
8841 AAAeDR AAB
8901 AAAeC+ AAD
8968 AAAeDL AAB
9108 AAAeDI AAD
9330 AAAeDP AAB
9396 AAAeDN AAG
9513 AAAeDM AAC
9702 AAAeDM AAE
9783 AAAeDL AAC
select distinct blocknumber from ( select id, substr(rowid,10,6) blocknumber , substr(rowid,16,3) rownumber from testsca where rownum < 100 order by id ) ;
BLOCKNUMBE
----------
AAAeC+
AAAeDR
AAAeC/
AAAeDK
AAAeDO
AAAeC8
AAAeDL
AAAeDP
AAAeDJ
AAAeC9
AAAeDI
BLOCKNUMBE
----------
AAAeDN
AAAeDS
AAAeC7
AAAeDM
15 rows selected.
同样写入 15 个块， 但是 访问时 被索引的值是分布在多个数据块里面进行排序。
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转载于:http://blog.itpub.net/16993226/viewspace-2148681/