高水位 HWM
高水位实验
]$ sqlplus /nolog
SQL*Plus: Release 10.2.0.3.0 - Production on Wed Nov 14 14:09:20 2012
Copyright (c) 1982, 2006, Oracle. All Rights Reserved.
SQL> conn oss03/oss03@oss2
Connected.
--设置下环境
SQL> set linesize 1000
SQL> set pagesize 100;
SQL> set timing on;
-- 删除要测试的表
SQL> drop table zfk_test;
Table dropped.
Elapsed: 00:00:00.64
--创建测试表的结构
SQL> create table zfk_test as select * from dba_objects where rownum<=0;
Table created.
Elapsed: 00:00:00.76
--表结构信息
-- Create table
create table ZFK_TEST
(
OWNER VARCHAR2(30),
OBJECT_NAME VARCHAR2(128),
SUBOBJECT_NAME VARCHAR2(30),
OBJECT_ID NUMBER,
DATA_OBJECT_ID NUMBER,
OBJECT_TYPE VARCHAR2(19),
CREATED DATE,
LAST_DDL_TIME DATE,
TIMESTAMP VARCHAR2(19),
STATUS VARCHAR2(7),
TEMPORARY VARCHAR2(1),
GENERATED VARCHAR2(1),
SECONDARY VARCHAR2(1)
)
tablespace OSS03_DATA
pctfree 10
initrans 1
maxtrans 255
storage
(
initial 64K
minextents 1
maxextents unlimited
);
--分析表
SQL> analyze table zfk_test compute statistics;
Table analyzed.
Elapsed: 00:00:00.74
--查看表信息 默认有8个空块
SQL> select blocks,empty_blocks,num_rows from user_tables where table_name='ZFK_TEST';
BLOCKS EMPTY_BLOCKS NUM_ROWS
---------- ------------ ----------
0 8 0
Elapsed: 00:00:00.02
--查看段信息 占了8个块
SQL> select segment_name,segment_type,blocks from dba_segments where segment_name='ZFK_TEST';
SEGMENT_NAME SEGMENT_TYPE BLOCKS
------------------------------ ------------------ ----------
ZFK_TEST TABLE 8
Elapsed: 00:00:00.25
--查看源表ID值
SQL> select min(object_id),max(object_id),count(object_id) from dba_objects;
MIN(OBJECT_ID) MAX(OBJECT_ID) COUNT(OBJECT_ID)
-------------- -------------- ----------------
2 504463 139255
Elapsed: 00:00:01.29
--插入100行数据
SQL> insert into zfk_test select * from dba_objects where object_id <=2+100;
101 rows created.
Elapsed: 00:00:00.08
SQL> commit;
SQL> col object_name for a30
SQL> col object_id for 99999999
SQL> select object_name,object_id from zfk_test where rownum<=10;
OBJECT_NAME OBJECT_ID
------------------------------ ---------
C_USER# 10
I_FILE#_BLOCK# 9
C_FILE#_BLOCK# 8
I_TS# 7
C_TS# 6
CLU$ 5
TAB$ 4
I_OBJ# 3
C_OBJ# 2
I_SEQ1 102
10 rows selected.
Elapsed: 00:00:00.00
--没有分析,表空块还是那么多
SQL> select blocks,empty_blocks,num_rows from user_tables where table_name='ZFK_TEST';
BLOCKS EMPTY_BLOCKS NUM_ROWS
---------- ------------ ----------
0 8 0
Elapsed: 00:00:00.03
-- 段空间没增大
SQL> select segment_name,segment_type,blocks from dba_segments where segment_name='ZFK_TEST';
SEGMENT_NAME SEGMENT_TYPE BLOCKS
------------------------------ ------------------ ----------
ZFK_TEST TABLE 8
Elapsed: 00:00:00.24
--再次分析看看
SQL> analyze table zfk_test compute statistics;
Table analyzed.
Elapsed: 00:00:00.26
--表段没有变大
SQL> select segment_name,segment_type,blocks from dba_segments where segment_name='ZFK_TEST';
SEGMENT_NAME SEGMENT_TYPE BLOCKS
------------------------------ ------------------ ----------
ZFK_TEST TABLE 8
Elapsed: 00:00:00.15
--表信息出现了 占用了5个块,3个空块,101行数据
SQL> select blocks,empty_blocks,num_rows from user_tables where table_name='ZFK_TEST';
BLOCKS EMPTY_BLOCKS NUM_ROWS
---------- ------------ ----------
5 3 101
Elapsed: 00:00:00.01
BLOCKS 列代表该表中曾经使用过得数据库块的数目，即水线。EMPTY_BLOCKS 代表分配给该表，但是在水线以上的数据库块，即从来没有使用的数据块.
SQL> insert into zfk_test select * from dba_objects where object_id <=102+1000;
1056 rows created.
Elapsed: 00:00:00.05
--先看看两个信息表
SQL> select blocks,empty_blocks,num_rows from user_tables where table_name='ZFK_TEST';
BLOCKS EMPTY_BLOCKS NUM_ROWS
---------- ------------ ----------
5 3 101
Elapsed: 00:00:00.00
SQL> select segment_name,segment_type,blocks from dba_segments where segment_name='ZFK_TEST';
SEGMENT_NAME SEGMENT_TYPE BLOCKS
------------------------------ ------------------ ----------
ZFK_TEST TABLE 24
Elapsed: 00:00:00.14
--段的空间会自动扩大
--分析下看看
SQL> analyze table zfk_test compute statistics;
Table analyzed.
Elapsed: 00:00:00.43
SQL> select segment_name,segment_type,blocks from dba_segments where segment_name='ZFK_TEST';
SEGMENT_NAME SEGMENT_TYPE BLOCKS
------------------------------ ------------------ ----------
ZFK_TEST TABLE 24
Elapsed: 00:00:00.15
SQL> select blocks,empty_blocks,num_rows from user_tables where table_name='ZFK_TEST';
BLOCKS EMPTY_BLOCKS NUM_ROWS
---------- ------------ ----------
20 4 1157
Elapsed: 00:00:00.00
--结论是 新追加数据是从表空间获取块或者说EXTENT区来分配给表段.没有经过分析就不会把高水位反应到表信息中去.
问题是如果查入数据或者APPEND方式高水位会自动改变吗?
--现在删除数据看看
SQL> delete zfk_test;
1157 rows deleted.
Elapsed: 00:00:00.02
SQL> commit;
Commit complete.
Elapsed: 00:00:00.02
SQL> select blocks,empty_blocks,num_rows from user_tables where table_name='ZFK_TEST';
BLOCKS EMPTY_BLOCKS NUM_ROWS
---------- ------------ ----------
20 4 1157
Elapsed: 00:00:00.02
SQL> select segment_name,segment_type,blocks from dba_segments where segment_name='ZFK_TEST';
SEGMENT_NAME SEGMENT_TYPE BLOCKS
------------------------------ ------------------ ----------
ZFK_TEST TABLE 24
Elapsed: 00:00:00.24
--一切都没有变化 再分析下看
SQL> analyze table zfk_test compute statistics;
Table analyzed.
Elapsed: 00:00:00.49
SQL> select segment_name,segment_type,blocks from dba_segments where segment_name='ZFK_TEST';
SEGMENT_NAME SEGMENT_TYPE BLOCKS
------------------------------ ------------------ ----------
ZFK_TEST TABLE 24
Elapsed: 00:00:00.15
SQL> select blocks,empty_blocks,num_rows from user_tables where table_name='ZFK_TEST';
BLOCKS EMPTY_BLOCKS NUM_ROWS
---------- ------------ ----------
20 4 0
Elapsed: 00:00:00.01
--删除数据不会降低高水位,分析后也不会,段空间也不会减少
SQL> alter table zfk_test deallocate unused;
Table altered.
Elapsed: 00:00:00.15
SQL> select blocks,empty_blocks,num_rows from user_tables where table_name='ZFK_TEST';
BLOCKS EMPTY_BLOCKS NUM_ROWS
---------- ------------ ----------
20 4 0
Elapsed: 00:00:00.00
SQL> select segment_name,segment_type,blocks from dba_segments where segment_name='ZFK_TEST';
SEGMENT_NAME SEGMENT_TYPE BLOCKS
------------------------------ ------------------ ----------
ZFK_TEST TABLE 24
--一个区控制8个块
SQL> select extent_id,block_id,blocks from dba_extents where segment_name='ZFK_TEST';
EXTENT_ID BLOCK_ID BLOCKS
---------- ---------- ----------
0 1966321 8
1 1966329 8
2 1966337 8
Elapsed: 00:00:00.55
--deallocate unused 释放的是 HWM 之上的数据块,但是还是要保留你整个表空间中extent的完整性
--因此4个空块不足以被释放
--再插巨量数据后
SQL> select count(*) from zfk_test;
COUNT(*)
----------
148218
Elapsed: 00:00:00.08
--删除
SQL> delete zfk_test where object_Id>1000;
147244 rows deleted.
Elapsed: 00:00:09.67
SQL> commit;
Commit complete.
Elapsed: 00:00:00.01
--查看段信息有4736个块
SQL> select segment_name,segment_type,blocks from dba_segments where segment_name='ZFK_TEST';
SEGMENT_NAME SEGMENT_TYPE BLOCKS
------------------------------ ------------------ ----------
ZFK_TEST TABLE 4736
Elapsed: 00:00:00.09
--释放未使用的块
SQL> alter table zfk_test deallocate unused;
Table altered.
Elapsed: 00:00:00.98
--释放了些块从段信息中
SQL> select segment_name,segment_type,blocks from dba_segments where segment_name='ZFK_TEST';
SEGMENT_NAME SEGMENT_TYPE BLOCKS
------------------------------ ------------------ ----------
ZFK_TEST TABLE 4648
Elapsed: 00:00:00.08
--表信息原来有95个空块
SQL> select blocks,empty_blocks,num_rows from user_tables where table_name='ZFK_TEST';
BLOCKS EMPTY_BLOCKS NUM_ROWS
---------- ------------ ----------
4641 95 145950
Elapsed: 00:00:00.01
--分析后块少了88个空块 位于高水位上的
SQL> analyze table zfk_test compute statistics;
Table analyzed.
Elapsed: 00:00:00.37
SQL> select blocks,empty_blocks,num_rows from user_tables where table_name='ZFK_TEST';
BLOCKS EMPTY_BLOCKS NUM_ROWS
---------- ------------ ----------
4641 7 29
Elapsed: 00:00:00.00
--查看区信息 最后个区从128块减少到40块.
SQL> select extent_id,block_id,blocks from dba_extents where segment_name='ZFK_TEST';
EXTENT_ID BLOCK_ID BLOCKS
---------- ---------- ----------
0 1966321 8
1 1966329 8
2 1966337 8
3 1966753 8
4 1966761 8
5 1966769 8
6 1966777 8
7 1966785 8
8 1966793 8
9 1966801 8
10 1966809 8
11 1966817 8
12 1966825 8
13 1966833 8
14 1966841 8
15 1966849 8
16 1966345 128
17 1966473 128
18 1966601 128
19 1966857 128
20 1966985 128
21 1967113 128
22 1967241 128
23 1967369 128
24 1967497 128
25 1967625 128
26 1967753 128
27 1967881 128
28 1968009 128
29 1968137 128
30 1968265 128
31 1968393 128
32 1968521 128
33 1968649 128
34 1968777 128
35 1969033 128
36 1969161 128
37 1969289 128
38 1969417 128
39 1969545 128
40 1969673 128
41 1969801 128
42 1969929 128
43 1970057 128
44 1970185 128
45 1970313 128
46 1970441 128
47 1970569 128
48 1978249 128
49 1964425 128
50 1964553 128
51 1964681 40
52 rows selected.
Elapsed: 00:00:00.79
--接下来再删,全部删除也无法释放了.因为高水位没有降低
--采用SHRINK方法释放
SQL> alter table zfk_test enable row movement;
Table altered.
Elapsed: 00:00:00.80
SQL> alter table zfk_test shrink space;
Table altered.
Elapsed: 00:00:00.36
SQL> select extent_id,block_id,blocks from dba_extents where segment_name='ZFK_TEST';
EXTENT_ID BLOCK_ID BLOCKS
---------- ---------- ----------
0 1966321 8
Elapsed: 00:00:00.89
SQL> select blocks,empty_blocks,num_rows from user_tables where table_name='ZFK_TEST';
BLOCKS EMPTY_BLOCKS NUM_ROWS
---------- ------------ ----------
20 4 0
Elapsed: 00:00:00.02
--段空间得到了释放,表的统计信息还是老样子的
SQL> analyze table zfk_test compute statistics;
Table analyzed.
Elapsed: 00:00:00.18
SQL> select blocks,empty_blocks,num_rows from user_tables where table_name='ZFK_TEST';
BLOCKS EMPTY_BLOCKS NUM_ROWS
---------- ------------ ----------
1 7 0
Elapsed: 00:00:00.01
SQL> insert into zfk_test select * from dba_objects;
139866 rows created.
Elapsed: 00:00:07.19
SQL> select blocks,empty_blocks,num_rows from user_tables where table_name='ZFK_TEST';
BLOCKS EMPTY_BLOCKS NUM_ROWS
---------- ------------ ----------
1 7 0
Elapsed: 00:00:00.00
-- 可以看到区16的时候管辖的块突然变成了128块
SQL> select extent_id,block_id,blocks from dba_extents where segment_name='ZFK_TEST';
EXTENT_ID BLOCK_ID BLOCKS
---------- ---------- ----------
0 1966321 8
1 1966329 8
2 1966337 8
3 1966345 8
4 1966353 8
5 1966361 8
6 1966369 8
7 1966377 8
8 1966385 8
9 1966393 8
10 1966401 8
11 1966409 8
12 1966417 8
13 1966425 8
14 1966433 8
15 1966441 8
16 1966473 128
17 1966601 128
18 1966857 128
19 1966985 128
20 1967113 128
21 1967241 128
22 1967369 128
23 1967497 128
24 1967625 128
25 1967753 128
26 1967881 128
27 1968009 128
28 1968137 128
29 1968265 128
30 1968393 128
31 1968521 128
32 1968649 128
33 1968777 128
34 rows selected.
Elapsed: 00:00:00.14
SQL> select segment_name,segment_type,blocks from dba_segments where segment_name='ZFK_TEST';
SEGMENT_NAME SEGMENT_TYPE BLOCKS
------------------------------ ------------------ ----------
ZFK_TEST TABLE 2432
Elapsed: 00:00:00.23
SQL> analyze table zfk_test compute statistics;
Table analyzed.
Elapsed: 00:00:04.18
SQL> select blocks,empty_blocks,num_rows from user_tables where table_name='ZFK_TEST';
BLOCKS EMPTY_BLOCKS NUM_ROWS
---------- ------------ ----------
2386 46 139866
Elapsed: 00:00:00.02
--有46个空块,当达不到EXTENT 128个块.
--TRUNCATE TABLE
SQL> truncate table zfk_test;
Table truncated.
Elapsed: 00:00:01.20
SQL> select blocks,empty_blocks,num_rows from user_tables where table_name='ZFK_TEST';
BLOCKS EMPTY_BLOCKS NUM_ROWS
---------- ------------ ----------
2386 46 139866
Elapsed: 00:00:00.03
SQL> select segment_name,segment_type,blocks from dba_segments where segment_name='ZFK_TEST';
SEGMENT_NAME SEGMENT_TYPE BLOCKS
------------------------------ ------------------ ----------
ZFK_TEST TABLE 8
Elapsed: 00:00:00.25
--TRUNCATE TABLE 会缩小段的空间
--删除再插入数据
SQL> insert into zfk_test select * from dba_objects;
139825 rows created.
Elapsed: 00:00:01.21
SQL> commit;
Commit complete.
Elapsed: 00:00:00.01
SQL> select segment_name,segment_type,blocks from dba_segments where segment_name='ZFK_TEST';
SEGMENT_NAME SEGMENT_TYPE BLOCKS
------------------------------ ------------------ ----------
ZFK_TEST TABLE 2432
Elapsed: 00:00:00.13
SQL> analyze table zfk_test compute statistics;
Table analyzed.
Elapsed: 00:00:02.93
SQL> select blocks,empty_blocks,num_rows from user_tables where table_name='ZFK_TEST';
BLOCKS EMPTY_BLOCKS NUM_ROWS
---------- ------------ ----------
2386 46 139825
Elapsed: 00:00:00.00
SQL> delete zfk_test where object_id >10000;
130222 rows deleted.
Elapsed: 00:00:05.64
SQL> commit;
Commit complete.
Elapsed: 00:00:00.05
--删除13,0222万 后段和表信息没有变化
SQL> select blocks,empty_blocks,num_rows from user_tables where table_name='ZFK_TEST';
BLOCKS EMPTY_BLOCKS NUM_ROWS
---------- ------------ ----------
2386 46 139825
Elapsed: 00:00:00.00
SQL> select segment_name,segment_type,blocks from dba_segments where segment_name='ZFK_TEST';
SEGMENT_NAME SEGMENT_TYPE BLOCKS
------------------------------ ------------------ ----------
ZFK_TEST TABLE 2432
Elapsed: 00:00:00.07
-- 分析后 表信息中的行数才剩9千条,当块和空块没有变化. 说明高水位下有大量的空块和空闲块
SQL> analyze table zfk_test compute statistics;
Table analyzed.
Elapsed: 00:00:00.24
SQL> select blocks,empty_blocks,num_rows from user_tables where table_name='ZFK_TEST';
BLOCKS EMPTY_BLOCKS NUM_ROWS
---------- ------------ ----------
2386 46 9603
Elapsed: 00:00:00.00
--再插入回数据去
SQL> insert into zfk_test select * from dba_objects where object_id>10000;
130222 rows created.
Elapsed: 00:00:00.84
SQL> commit;
Commit complete.
Elapsed: 00:00:00.02
--查看下段和表信息 都没有发生变化
SQL> select blocks,empty_blocks,num_rows from user_tables where table_name='ZFK_TEST';
BLOCKS EMPTY_BLOCKS NUM_ROWS
---------- ------------ ----------
2386 46 9603
Elapsed: 00:00:00.03
SQL> select segment_name,segment_type,blocks from dba_segments where segment_name='ZFK_TEST';
SEGMENT_NAME SEGMENT_TYPE BLOCKS
------------------------------ ------------------ ----------
ZFK_TEST TABLE 2432
Elapsed: 00:00:00.26
--分析后 表的行数变化了
SQL> analyze table zfk_test compute statistics;
Table analyzed.
Elapsed: 00:00:03.74
SQL> select blocks,empty_blocks,num_rows from user_tables where table_name='ZFK_TEST';
BLOCKS EMPTY_BLOCKS NUM_ROWS
---------- ------------ ----------
2386 46 139825
Elapsed: 00:00:00.00
--说明插入到高水位下面的空闲块里了
---APPEND
SQL> insert /*+append*/ into zfk_test select * from dba_objects where object_id>10000;
130224 rows created.
Elapsed: 00:00:27.13
SQL> select segment_name,segment_type,blocks from dba_segments where segment_name='ZFK_TEST';
SEGMENT_NAME SEGMENT_TYPE BLOCKS
------------------------------ ------------------ ----------
ZFK_TEST TABLE 4736
Elapsed: 00:00:00.24
--- Append 删除居然会报错 这个问题待日后研究下
SQL> delete zfk_test where object_id>10000;
delete zfk_test where object_id>10000
*
ERROR at line 1:
ORA-12838: cannot read/modify an object after modifying it in parallel
insert /*+append*/ 如果不commit的话，会对该表加6级锁，也就是说，即使此时select这个表都会报错。
因此append提示的语句首先不能是业务表，其次要尽快提交
SQL> analyze table zfk_test compute statistics;
Table analyzed.
Elapsed: 00:00:04.19
SQL> delete zfk_test where object_id>10000;
130224 rows deleted.
Elapsed: 00:00:04.00
--- 这方式的APPEND 是普通方式插入的
SQL> insert into /*+append*/ zfk_test select * from dba_objects where object_id >10000;
129986 rows created.
Elapsed: 00:00:01.18
SQL> commit;
Commit complete.
Elapsed: 00:00:00.04
SQL> select segment_name,segment_type,blocks from dba_segments where segment_name='ZFK_TEST';
SEGMENT_NAME SEGMENT_TYPE BLOCKS
------------------------------ ------------------ ----------
ZFK_TEST TABLE 4736
Elapsed: 00:00:00.14
--删除所有数据 使用下面查看表段具体使用多少个块,就是非空闲块有多少?
SQL> select count(distinct dbms_rowid.rowid_block_number(rowid)|| dbms_rowid.rowid_relative_fno(rowid)) "used" from zfk_test;
used
----------
0
Elapsed: 00:00:00.10
--插入1万条进去
SQL> insert into zfk_test select * from dba_objects where object_id <10000;
9582 rows created.
Elapsed: 00:00:00.12
SQL> commit;
Commit complete.
Elapsed: 00:00:00.02
-- 显示使用了119个块
SQL> select count(distinct dbms_rowid.rowid_block_number(rowid)|| dbms_rowid.rowid_relative_fno(rowid)) "used" from zfk_test;
used
----------
119
Elapsed: 00:00:00.37
-- 分析后 段和表信息都没有反应,还是那么多块.
SQL> analyze table zfk_test compute statistics;
Table analyzed.
Elapsed: 00:00:01.02
SQL> select segment_name,segment_type,blocks from dba_segments where segment_name='ZFK_TEST';
SEGMENT_NAME SEGMENT_TYPE BLOCKS
------------------------------ ------------------ ----------
ZFK_TEST TABLE 4648
Elapsed: 00:00:00.25
SQL> select blocks,empty_blocks,num_rows from user_tables where table_name='ZFK_TEST';
BLOCKS EMPTY_BLOCKS NUM_ROWS
---------- ------------ ----------
4641 7 9582
Elapsed: 00:00:00.03
-- Shrink下
SQL> alter table zfk_test enable row movement;
Table altered.
Elapsed: 00:00:00.18
SQL> alter table zfk_test shrink space;
Table altered.
Elapsed: 00:00:19.25
SQL> select segment_name,segment_type,blocks from dba_segments where segment_name='ZFK_TEST';
SEGMENT_NAME SEGMENT_TYPE BLOCKS
------------------------------ ------------------ ----------
ZFK_TEST TABLE 128
Elapsed: 00:00:00.14
SQL> analyze table zfk_test compute statistics;
Table analyzed.
Elapsed: 00:00:00.35
SQL> select blocks,empty_blocks,num_rows from user_tables where table_name='ZFK_TEST';
BLOCKS EMPTY_BLOCKS NUM_ROWS
---------- ------------ ----------
113 15 9582
Elapsed: 00:00:00.01
-- Shrink后 分析所得 从原来的119块使用变成了113个块,也就是说Shrink 不仅降低高水位,释放空块,还整理碎块功效!
SQL> select count(distinct dbms_rowid.rowid_block_number(rowid)|| dbms_rowid.rowid_relative_fno(rowid)) "used" from zfk_test;
used
----------
113
Elapsed: 00:00:00.25
总结
1 高水位随着数据增多而向上扩展,这个是自动的.
2 如果块不够用了,就分配1个新的区给段,这个区含有的块可以指定,可以ORACLE自动分配.
3 高水位上面的空间 是未使用过的空块,当这些空块数量不会超过一个区EXTENT
4 段的大小随者数据增大而得到反映在信息表中,
5 表信息表不会随者数据的变化而得到反应,除非通过分析获得.
6 alter table shrink space;和truncate talbe 才可以降低高水位标志,并且释放段的空间
7 Alter table table_name deallocate unused 只能释放高水位上未使用的空块,无法降低高水位
8 查看表段使用多少个块
select count(distinct dbms_rowid.rowid_block_number(rowid)|| dbms_rowid.rowid_relative_fno(rowid)) "used" from table_name