Understanding the storage structure 2

Take up the article http://blog.csdn.net/ashic/article/details/44117867
In the previous article we dump out the L1 L2 L3 block, and now let's look at the information contained in them

content	Notes
L1	First Level BITMAP BLOCK
L2	SECOND level BITMAP BLOCK
L3 (segment head)	Pagetable SEGMENT HEADER

Look at the dump file through the table above and we can clearly find out
In this uniform size 1M table space, there are two L1 blocks in a zone, and 1 l2,1 L3

In the first L1 block

Dump ofFirst Level Bitmap Block--------------------------------Nbits:4Nranges:1Parent DBA:0x01800082Poffset:0Unformatted: -Total -         FirstUseful BLOCK:4Owning instance:1Instance ownership changed at Geneva/ -/ -  -: +: -Last Successful SearchGeneva/ -/ -  -: +: -Freeness STATUS:NF10Nf20Nf30Nf40Extent Map Block Offset:4294967295First free DataBlock:4Bitmap block Lock opcode9Locker XID::0x0006. 020. 00000594Dealloc SCN:2275418.0Flag:0x00000021(OBJD/-/-/-/-/HWM) Inc#: 0 objd:77412HWM FLAG:HWM Set highwater::0x01800084Ext#: 0 blk#: 4 ext size:128  #blocks in seg. HDR ' s freelists:0  #blocks below:0Mapblk0x00000000  Offset:0     

The parent dba:0x01800082 table is the L2 block location that manages it

can be passed dbms_utility. Data_block_address Package comes out L1 block position

[email protected]>select dbms_utility.data_block_address_file(TO_NUMBER(‘&entervalue‘‘XXXXXXXX‘)) file_id,dbms_utility.data_block_address_block(TO_NUMBER(‘&entervalue‘‘XXXXXXXX‘fromvaluefor01800082valuefor01800082   FILE_ID   BLOCK_ID---------- ----------         6        130

Unformatted:60 total:64 First Useful block:4

Represents the unformatted block has 60, this L1 manages 64 blocks of data altogether, the first usable data block is 4th number block, namely 6th number file 132th number block

Set      Highwater::  0x01800084  ext#: 0      blk#: 4      ext size: 128   

High water level first in 0x01800084 is the 132th good block of document 6th, this is because the fan table in my experiment was truncate no data, so the high watermark in the first available block

One thing to note is that the move rule for high watermark in ASSM is: When the first row is inserted in the zone, the high water point moves to the first L1 of the zone
The largest chunk of data in the block. After moving to the largest chunk of data in the second L2 block, and so on

ext#:0 Indicates the first area of the
BLK#:4 Fourth block
Ext size:128 The area consists of 128 blocks

--------------------------------------------------------DBA Ranges :--------------------------------------------------------0x01800080  Length:  -     Offset: 0         0: Metadata   1: Metadata   2: Metadata   3: Metadata   4: Unformatted   5: Unformatted   6: Unformatted   7: Unformatted   8: Unformatted   9: Unformatted   Ten: Unformatted    One: Unformatted    A: Unformatted    -: Unformatted    -: Unformatted    the: Unformatted    -: Unformatted    -: Unformatted    -: Unformatted    +: Unformatted    -: Unformatted    +: Unformatted    A: Unformatted    at: Unformatted    -: Unformatted    -: Unformatted    -: Unformatted    -: Unformatted    -: Unformatted    in: Unformatted    -: Unformatted    to: Unformatted    +: Unformatted    -: Unformatted    the: Unformatted    *: Unformatted    $: Unformatted   Panax Notoginseng: Unformatted    -: Unformatted    the: Unformatted    +: Unformatted    A: Unformatted    the: Unformatted    +: Unformatted    -: Unformatted    $: Unformatted    $: Unformatted    -: Unformatted    -: Unformatted    the: Unformatted    -: Unformatted   Wuyi: Unformatted    the: Unformatted    -: Unformatted    Wu: Unformatted    -: Unformatted    About: Unformatted    $: Unformatted    -: Unformatted    -: Unformatted    -: Unformatted    A: Unformatted    +: Unformatted    the: Unformatted--------------------------------------------------------

0x01800080 represents the location of the L1 block
can be passed dbms_utility. Data_block_address Package comes out L1 block position

[email protected]>set verify off[email protected]>select dbms_utility.data_block_address_file(TO_NUMBER(‘&entervalue‘‘XXXXXXXX‘)) file_id,dbms_utility.data_block_address_block(TO_NUMBER(‘&entervalue‘‘XXXXXXXX‘fromvaluefor01800080valuefor01800080   FILE_ID   BLOCK_ID---------- ----------         6        128

The block number is actually not a bag.

Look, we can see that we've managed 64 blocks of data, the 128~191 block, in the L1 block.
Use of >75%,50%-75%,25%-50% and <25% to mark blocks
At present, our L1 management of the 64 block 0~3 block is metadata block, that is, 128,129,130,131 pieces
4~63 These 60 blocks are data blocks with a status of unformatted unformatted

What is unformatted?

As we said in the previous article, the table ID and the segment ID are the same in the initial case

[email protected]>selectfromwhere object_name=‘FAN‘; OBJECT_ID DATA_OBJECT_ID---------- --------------     77411          77411

The table ID does not change once it is created, but the segment ID changes, such as when the table is truncate

scott@PROD>truncate table fan;Tabletruncated.scott@PROD>select object_id,data_object_id from dba_objects where object_name=‘FAN‘OBJECT_IDDATA_OBJECT_ID------------------------     77411          77412

After the Segment ID and table ID are different, the formatted block is the seg/obj number of the record in the block is the segment ID
Unformatted is the same as the segment ID before truncate.
You can dump an unformatted quick view of the seg/obj, compare it and know, I will not do the experiment

Keep looking at the L2 block.

The second L1 and the first L1 almost, did not say, see L2

dump of  Second Level Bitmap Block number : 2  nfree: 2  ffree: 0  pdba: 0x018000  Inc class= "hljs-comment" >#: 0 objd:77412  opcode:4  xid:l1 Ranges: -------------------------------------------------------- 0x01800080  free: 5  Inst: 1  Span class= "Hljs-number" >0x01800081  free: 5  Inst: 1  -------------------------------------------------- ------

The address of the address 0x01800083 and L1 blocks of the PDBA and L3 blocks is recorded in the L2 block.
What do you mean here free:5 I don't know, ╮ (╯_╰) ╭, who knows tell me

L3 Block

Extent Control Header-----------------------------------------------------------------Extent Header:: spare1:0Spare2:0      #extents: 1 #blocks:                   LastMap0x00000000  #maps: 0 offset:2716Highwater::0x018000c0Ext#: 0 blk#: 4 ext size:128  #blocks in seg. HDR ' s freelists:0  #blocks below:0Mapblk0x00000000  Offset:0Unlocked--------------------------------------------------------Low Highwater Mark:highwater::0x01800084Ext#: 0 blk#: 4 ext size:128  #blocks in seg. HDR ' s freelists:0  #blocks below:0Mapblk0x00000000  Offset:0Level1BMB forHigh HWM BLOCK:0x01800080Level1BMB forLow HWM BLOCK:0x01800080

The note here is Highwater:: 0x018000c0 low Highwater Mark
: 0x01800084 low and high water level line

A block that has been formatted when the low high watermark is below
The block between the low high water level and the high water level may be formatted, or there may be no
A description of an official document

All you have to remember is that the full table scan usually reads to the low high watermark and then reads the formatted block from the low height to the high with the bitmap, avoiding the unformatted block
The easiest way to see the high watermark is the dump header block.

[email protected]>selectfromwhere segment_name=‘FAN‘and owner=‘SCOTT‘;HEADER_FILE HEADER_BLOCK----------- ------------          6          131

The above command makes it easy to find the segment head block

--------------------------------------------------------Segment type:1 nl2:1 blksz:8192 fbsz:0 L2 ArrayStartOffset0x00001434   First  Level 3BMB:0x00000000L2 Hint forInserts:0x01800082   Last  Level 1BMB:0x01800081   Last  LevelII BMB:0x01800082   Last  LevelIII BMB:0x00000000Map Header::Next  0x00000000#extents:1obj#:77412Flag0x10000000INC #0 

content	Notes
First Level 3 bmb:0x00000000	The library is large, the area is super, the block is too long to appear
Last Level 1 bmb:0x01800081	The address of the last L1 BMB
Last level II bmb:0x01800082	The address of the last L2 BMB
Last level III bmb:0x0000000	The address of the last L3 BMB

Extent Map  -----------------------------------------------------------------   0x01800080  length: 128   

Information for the area recorded in the L3
The first zone starts from 0x01800080, but it is important to note that the full table scan is not the area map that Oracle reads.
But the following.

Auxillary Map  --------------------------------------------------------   Extent 0     :  L1 dba:  0x01800080 Data dba:  0x01800084  --------------------------------------------------------   Second Level Bitmap block DBAs    --------------------------------------------------------   DBA 1:   0x01800082

Zone 0 first L1 for 0x01800080 first non-metadata data block is 0x01800084
Oracle full scan is based on the DBA lookup zone after "Data DBA: * *". But there is no area length, so the above section of the map information is still to be read.

Understanding the storage structure 2