[20140731]关于LOB字段存储特性4.txt
--12c开始建立表如果包含lob，缺省建立的是securefile，securefile支持一些新特性，比如： Deduplication, Compression and Encryption.
--在11g下测试securefile看看。
SCOTT@test> @ver
BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production
CREATE TABLE "SCOTT"."T1"
( "ID" NUMBER,
"IDX" NUMBER,
"COL1" CLOB,
"COL2" CLOB,
"COL3" CLOB
)
LOB ("COL1") STORE AS SECUREFILE
LOB ("COL2") STORE AS SECUREFILE
LOB ("COL3") STORE AS SECUREFILE (disable storage in row);
create unique index i_t1_id on t1(id);
insert into t1 values (1,1,lpad('a',100,'a'),lpad('b',4000,'b'),lpad('c',4000,'c'));
commit ;
execute dbms_stats.gather_table_stats(user,'t1',cascade=>true,method_opt=>'for all columns size 1',no_invalidate=>false);
--安装的语言选择NLS_LANG=SIMPLIFIED CHINESE_CHINA.ZHS16GBK.这样即使1个英文字符也占用2个字节.
--这样都是插入8000字节,lob的信息保存在块外（我的数据库是8k的).
--题外话题:最好使用blob类型,这样可以原样保存,特别保存的文本是英文的情况下,空间浪费比较严重,对于中文字符集.
--col1=lpad('a',100,'a'),应该在块内。
--col2=lpad('b',4000,'b'),长度超出3964，应该在块外。
--col3=lpad('c',4000,'c'),使用DISABLE STORAGE IN ROW，无论如何都在块外。
SCOTT@test> SELECT DBMS_METADATA.get_ddl ('TABLE','T1') from dual ;
DBMS_METADATA.GET_DDL('TABLE','T1')
----------------------------------------------------------------------------
CREATE TABLE "SCOTT"."T1"
( "ID" NUMBER,
"IDX" NUMBER,
"COL1" CLOB,
"COL2" CLOB,
"COL3" CLOB
) SEGMENT CREATION IMMEDIATE
PCTFREE 10 PCTUSED 40 INITRANS 1 MAXTRANS 255
NOCOMPRESS LOGGING
STORAGE(INITIAL 65536 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645
PCTINCREASE 0 FREELISTS 1 FREELIST GROUPS 1
BUFFER_POOL DEFAULT FLASH_CACHE DEFAULT CELL_FLASH_CACHE DEFAULT)
TABLESPACE "USERS"
LOB ("COL1") STORE AS SECUREFILE (
TABLESPACE "USERS" ENABLE STORAGE IN ROW CHUNK 8192
NOCACHE LOGGING NOCOMPRESS KEEP_DUPLICATES
STORAGE(INITIAL 106496 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645
PCTINCREASE 0
BUFFER_POOL DEFAULT FLASH_CACHE DEFAULT CELL_FLASH_CACHE DEFAULT))
LOB ("COL2") STORE AS SECUREFILE (
TABLESPACE "USERS" ENABLE STORAGE IN ROW CHUNK 8192
NOCACHE LOGGING NOCOMPRESS KEEP_DUPLICATES
STORAGE(INITIAL 106496 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645
PCTINCREASE 0
BUFFER_POOL DEFAULT FLASH_CACHE DEFAULT CELL_FLASH_CACHE DEFAULT))
LOB ("COL3") STORE AS SECUREFILE (
TABLESPACE "USERS" DISABLE STORAGE IN ROW CHUNK 8192
NOCACHE LOGGING NOCOMPRESS KEEP_DUPLICATES
STORAGE(INITIAL 106496 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645
PCTINCREASE 0
BUFFER_POOL DEFAULT FLASH_CACHE DEFAULT CELL_FLASH_CACHE DEFAULT))
SCOTT@test> set autot trace
SCOTT@test> select id,idx from t1 where id=1;
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
2 consistent gets
0 physical reads
0 redo size
--注意如果出现recursive calls0,可以执行多次。可以发现仅仅2个逻辑读。
SCOTT@test> select id,col1 from t1 where id=1;
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
2 consistent gets
0 physical reads
0 redo size
--col1的信息长度
SCOTT@test> select id,col2 from t1 where id=1;
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
4 consistent gets
2 physical reads
0 redo size
--如果col2是ENABLE STORAGE IN ROW,由于长度大于3964,保存在块外,导致 consistent gets增加到4,同时存在
--2个physical reads,无论执行多少次.
SCOTT@test> select id,col3 from t1 where id=1;
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
4 consistent gets
2 physical reads
0 redo size
--对比发现，ENABLE/DISABLE STORAGE IN ROW两者的逻辑读一样对于securefile，都是4个逻辑读，而且每次都是2个物理读。
--在块内字段col1外，执行的语句select id,idx from t1 where id=1 与select id,col1 from t1 where id=1，两者的逻辑读一样。
先做一个转储：
SCOTT@test> select rowid,id,idx from t1 where id=1;
ROWID ID IDX
------------------ ---------- ----------
AABGjbAAEAAAAWmAAA 1 1
SCOTT@test> @lookup_rowid AABGjbAAEAAAAWmAAA
OBJECT FILE BLOCK ROW DBA TEXT
---------- ---------- ---------- ---------- -------------------- ----------------------------------------
288987 4 1446 0 4,1446 alter system dump datafile 4 block 1446
SCOTT@test> alter system dump datafile 4 block 1446;
System altered.
Block header dump: 0x010005a6
Object id on Block? Y
seg/obj: 0x468db csc: 0x02.a6127dc2 itc: 2 flg: E typ: 1 - DATA
brn: 0 bdba: 0x10005a0 ver: 0x01 opc: 0
inc: 0 exflg: 0
Itl Xid Uba Flag Lck Scn/Fsc
0x01 0x0005.000.00006a25 0x00c002fb.2321.1e --U- 1 fsc 0x0000.a6127ee0
0x02 0x0000.000.00000000 0x00000000.0000.00 ---- 0 fsc 0x0000.00000000
bdba: 0x010005a6
data_block_dump,data header at 0x2a9751e264
===============
tsiz: 0x1f98
hsiz: 0x14
pbl: 0x2a9751e264
76543210
flag=--------
ntab=1
nrow=1
frre=-1
fsbo=0x14
fseo=0x1e5a
avsp=0x1e46
tosp=0x1e46
0xe:pti[0] nrow=1 offs=0
0x12:pri[0] offs=0x1e5a
block_row_dump:
tab 0, row 0, @0x1e5a
tl: 318 fb: --H-FL-- lb: 0x1 cc: 5
col 0: [ 2] c1 02
col 1: [ 2] c1 02
col 2: [230]
00 54 00 01 02 0c 80 80 00 02 00 00 00 01 00 00 02 35 33 cd 00 d2 48 90 00
cc 00 00 c8 01 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61
00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00
61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61
00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00
61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61
00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00
61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61
00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00
61 00 61 00 61
LOB
Locator:
Length: 84(230)
Version: 1
Byte Length: 2
LobID: 00.00.00.01.00.00.02.35.33.cd
Flags[ 0x02 0x0c 0x80 0x80 ]:
Type: CLOB
Storage: SecureFile
Characterset Format: IMPLICIT
Partitioned Table: No
Options: VaringWidthReadWrite
SecureFile Header:
Length: 210
Old Flag: 0x48 [ DataInRow SecureFile ]
Flag 0: 0x90 [ INODE Valid ]
Layers:
Lengths Array: INODE:204
INODE:
00 00 c8 01 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61
00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61
00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61 00 61
col 3: [38]
00 54 00 01 02 0c 80 80 00 02 00 00 00 01 00 00 02 35 33 ce 00 12 40 90 00
0c 21 00 1f 40 01 00 01 01 00 02 a3 01
LOB
Locator:
Length: 84(38)
Version: 1
Byte Length: 2
LobID: 00.00.00.01.00.00.02.35.33.ce
Flags[ 0x02 0x0c 0x80 0x80 ]:
Type: CLOB
Storage: SecureFile
Characterset Format: IMPLICIT
Partitioned Table: No
Options: VaringWidthReadWrite
SecureFile Header:
Length: 18
Old Flag: 0x40 [ SecureFile ]
Flag 0: 0x90 [ INODE Valid ]
Layers:
Lengths Array: INODE:12
INODE:
21 00 1f 40 01 00 01 01 00 02 a3 01
col 4: [38]
00 54 00 01 02 0c 80 80 00 02 00 00 00 01 00 00 02 35 33 cf 00 12 40 90 00
0c 21 00 1f 40 01 00 01 01 00 02 bb 01
LOB
Locator:
Length: 84(38)
Version: 1
Byte Length: 2
LobID: 00.00.00.01.00.00.02.35.33.cf
Flags[ 0x02 0x0c 0x80 0x80 ]:
Type: CLOB
Storage: SecureFile
Characterset Format: IMPLICIT
Partitioned Table: No
Options: VaringWidthReadWrite
SecureFile Header:
Length: 18
Old Flag: 0x40 [ SecureFile ]
Flag 0: 0x90 [ INODE Valid ]
Layers:
Lengths Array: INODE:12
INODE:
21 00 1f 40 01 00 01 01 00 02 bb 01
end_of_block_dump
End dump data blocks tsn: 4 file#: 4 minblk 1446 maxblk 1446
-- 对比col 3: [38]与col 4: [38]，块内的长度都是一样的。
col 3: [38]
00 54 00 01 02 0c 80 80 00 02 00 00 00 01 00 00 02 35 33 ce 00 12 40 90 00
0c 21 00 1f 40 01 00 01 01 00 02 a3 01
col 4: [38]
00 54 00 01 02 0c 80 80 00 02 00 00 00 01 00 00 02 35 33 cf 00 12 40 90 00
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~lobid
0c 21 00 1f 40 01 00 01 01 00 02 bb 01
~~~~~~~~~~~
如果参考URL http://juliandyke.com/Presentations/LOBInternals.ppt，后面的
01 00 02 bb 表示 DBA of first block in extent
01 表示 # Blocks in extent
SCOTT@test> @dfb 010002a3
RFILE# BLOCK#
---------- ----------
4 675
TEXT
----------------------------------------
alter system dump datafile 4 block 675 ;
SCOTT@test> @dfb 010002bb
RFILE# BLOCK#
---------- ----------
4 699
TEXT
----------------------------------------
alter system dump datafile 4 block 699 ;
--转储对应的块：
alter system dump datafile 4 block 675 ;
Block header dump: 0x010002a3
Object id on Block? Y
seg/obj: 0x468de csc: 0x02.a6127d14 itc: 1 flg: E typ: 5 - LOCAL LOBS
fsl: 0 fnx: 0xffffffff ver: 0x01
Itl Xid Uba Flag Lck Scn/Fsc
0x01 0x0005.000.00006a25 0x00000000.0000.00 -B-- 0 fsc 0x0000.00000000
========
bdba [0x010002a3]
kdlich [0x2a9751e24c 56]
flg0 0x20 [ver=0 typ=data lock=n]
flg1 0x00
scn 0x0002.a6127d14
lid 000000010000023533ce
rid 0x00000000.0000
kdlidh [0x2a9751e264 24]
flg2 0x00 [ver=0 lid=short-rowid hash=n cmap=n pfill=n]
flg3 0x00
pskip 0
sskip 0
hash 0000000000000000000000000000000000000000
hwm 8000
spr 0
data [0x2a9751e280 52 8060]
00 62 00 62 00 62 00 62 00 62 00 62 00 62 00 62 00 62 00 62 00 62 00 62 00 62
00 62 00 62 00 62 00 62 00 62 00 62 00 62 00 62 00 62 00 62 00 62 00 62 00 62
....
00 62 00 62 00 62 00 62 00 62 00 62 00 62 00 62 00 62 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
--- end of lob block dump ---
End dump data blocks tsn: 4 file#: 4 minblk 675 maxblk 675
alter system dump datafile 4 block 699 ;
Block header dump: 0x010002bb
Object id on Block? Y
seg/obj: 0x468e0 csc: 0x02.a6127dc0 itc: 1 flg: E typ: 5 - LOCAL LOBS
fsl: 0 fnx: 0xffffffff ver: 0x01
Itl Xid Uba Flag Lck Scn/Fsc
0x01 0x0005.000.00006a25 0x00000000.0000.00 -B-- 0 fsc 0x0000.00000000
========
bdba [0x010002bb]
kdlich [0x2a9751e24c 56]
flg0 0x20 [ver=0 typ=data lock=n]
flg1 0x00
scn 0x0002.a6127dc0
lid 000000010000023533cf
rid 0x00000000.0000
kdlidh [0x2a9751e264 24]
flg2 0x00 [ver=0 lid=short-rowid hash=n cmap=n pfill=n]
flg3 0x00
pskip 0
sskip 0
hash 0000000000000000000000000000000000000000
hwm 8000
spr 0
data [0x2a9751e280 52 8060]
00 63 00 63 00 63 00 63 00 63 00 63 00 63 00 63 00 63 00 63 00 63 00 63 00 63
00 63 00 63 00 63 00 63 00 63 00 63 00 63 00 63 00 63 00 63 00 63 00 63 00 63
...
00 63 00 63 00 63 00 63 00 63 00 63 00 63 00 63 00 63 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
--- end of lob block dump ---
End dump data blocks tsn: 4 file#: 4 minblk 699 maxblk 699
--从这些可以看出对于使用securefile，无论使用ENABLE/DISABLE STORAGE IN ROW,在块内保存有chunk的信息,不需要通过lob index来定位,能获得很好的性能。
--不知道什么情况下通过lib index来定位????
SCOTT@test> alter table t1 modify lob (col2) (CACHE) modify lob (col3) (cache);
Table altered.
SCOTT@test> select id,col2 from t1 where id=1;
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
6 consistent gets
0 physical reads
0 redo size
SCOTT@test> select id,col3 from t1 where id=1;
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
6 consistent gets
0 physical reads
0 redo size
--可以发现设置cache后，多次执行physical reads=0.
--看来以后设置lob为securefile比较好一些。
