Oracle ASSM three-bit block structure

Apr 8 posted in Oracle (RSS), 151 views.

Piner a few days ago issued a reward: the three-bit block ASSM find the article, at the same time give a guess for the structure of ASSM.

The structure and Piner guess my imagination is different from the structure of ASSM in my opinion should be as follows:

That is to say in my opinion the structure of BMB should be balanced, while the first paragraph of PAGETABLE SEGMENT HEADER simultaneously serve as the first bit 0 Block 3 role.

Medium at PAGETABLE SEGMENT HEADER in fact we can easily see this output:

-------------------------------------------------- ------
Segment Type: 1 nl2: 103 blksz: 2048 fbsz: 0
L2 Array start offset: 0x00000434
First Level 3 BMB: 0x00000000
L2 Hint for inserts: 0x0355cfad
Last Level 1 BMB: 0x03560c9c
Last Level II BMB: 0x0355cfad
Last Level III BMB: 0x00000000
Map Header:: next 0x034000bf # extents: 51 obj #: 33141 flag: 0x20000000
Extent Map
-------------------------------------------------- ---------------

In other words, here records the First Level 3 BMB and Last Level III BMB address, then this is enough, there can be two-way pointer class to Level 3-bit block of navigation, which is the first three bitmap 0 block that is the first paragraph, and no need to record all 3-bit block address.

Generated because of a 3-bit block is not easy, so to reward only Piner, 873G, he constructed a large table, still do not have other three-bit block:

SQL> select bytes/1024/1024/1024 "SIZE (G)" from user_segments where segment_name = 'TEST';

SIZE (G)
----------
873.25

Search for 3-bit block, I started to do the following experiment to be able to:
1. Express faster implementation and expansion of the range distribution
2. To make the first 3-bit 0 Block segment header that is as small as possible in order to further expand

To this end I created a table 2k block_size space uniform size range of the size of 10K, so the space can be seen as far as possible consumption:

SQL> create tablespace eygle
2 datafile 'd: \ EYGLE01.DBF' size 1024M reuse blocksize 2048
3 extent management local uniform size 10k
4 segment space management auto;
Table space has been created.

SQL> set timing on
SQL> alter tablespace eygle add datafile 'f: \ eygle02.dbf' size 8191M reuse;

Table space has been changed.

Has spent time: 00: 44: 42.08

Note that the addition of a data file 8G, took me 44 minutes, this is a Windows platform, unusually slow.

And create a data table, set a high value pctfree, making each Block and his only store data, then insert one of millions of records:

SQL> create table EYGLE
2 (
3 ID NUMBER (8),
4 UNAME CHAR (1000)
5)
6 tablespace eygle
7 pctfree 50
8 initrans 1
9 maxtrans 255
10;
Table has been created.

Has spent time: 00: 00: 00.00
SQL> begin
2 for i in 1 .. 100 loop
3 for i in 1 .. 100000 loop
4 insert into eygle values (i, 'eygle');
5 end loop;
6 commit;
7 end loop;
8 end;
9 /

After the completion of these operations, the table space used around 9G:

SQL> select bytes/1024/1024/1024 sizegb from dba_segments
2 where segment_name = 'EYGLE';
SIZEGB
----------
8.9988327

At this point the first three-bit block there, This is how valuable a three-bit block ah:

Start dump data blocks tsn: 12 file #: 13 minblk 4032222 maxblk 4032222
buffer tsn: 12 rdba: 0x037d86de (13/4032222)
scn: 0x0000.00bdc864 seq: 0x01 flg: 0x04 tail: 0xc8642201
frmt: 0x02 chkval: 0xf597 type: 0x22 = THIRD LEVEL BITMAP BLOCK
Dump of Third Level Bitmap Block
number: 9, next: 0x00000000
L2 Ranges:
-------------------------------------------------- ------
0x037d86dd
0x037dd22d 0x037e1d7d 0x037e68cd 0x037eb41d
0x037eff6d 0x037f4abd 0x037f960d 0x037fe15d

-------------------------------------------------- ------
End dump data blocks tsn: 12 file #: 13 minblk 4032222 maxblk 4032222

Bitmap on the existence on a downward pointer: next: 0x00000000, of course, there is no value, we can generate a 3-bit block to observe.

Well enough in fact to have been here, my icon has been enough of that.