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db2 block archtiecture

Hi ,

Where can i find information about db2 block structure? I want to know
how it stores rows into blocks , how it handles issues such as row
migration / chaining or etc.
Kind Regards,
hope

Nov 12 '05 #1
4 3122
In IBM jargon (as long as UDB is concerned), a block is referred to as
a page. The following information are some abstracts from the
Administration (Planning) document of UDB.

##########################
By default, table data is stored on 4 KB pages. Each page (regardless
of page size) contains 68 bytes of overhead for the database manager.
This leaves 4028 bytes to hold user data (or rows), although no row on
a 4 KB page can exceed 4005 bytes in length. A row will not span
multiple pages.

Rows are usually inserted into a table in first-fit order. The file is
searched (using a free space map) for the first available space that is
large enough to hold the new row. When a row is updated, it is updated
in place, unless there is insufficient space left on the page to
contain it. If this is the case, a record is created in the original
row location that points to the new location in the table file of the
updated row.

If the ALTER TABLE APPEND ON statement is invoked, data is always
appended, and information about any free space on the data pages is not
kept.

There is a maximum of only 255 rows per page.
##########################

I don't know whether this answers your query or not, but I suggest in
order to dig further, you refer to the UDB documentation. The URL for
the same is: http://publib.boulder.ibm.com/infoce...help/index.jsp
regards,
dotyet

Nov 12 '05 #2
phu
Hi,

I think a lot of that would be proprietory (sp?) information. However,
if you search google for "db2 internals", you will see that there
are occasional presentations given.

I also think that some information about the page layout is also
discussed in the online documentation (e.g. Performance). I don't think
you will find anything on migration or chaining, however.

Good luck :)
Bill

hopehope_123 <ho**********@yahoo.com> wrote:
Hi , Where can i find information about db2 block structure? I want to know
how it stores rows into blocks , how it handles issues such as row
migration / chaining or etc.
Kind Regards,
hope


--
Bill Phu -- Dalhousie University (phu at cs dal ca)
"Three grand essentials to happiness in this life are something to do,
something to love, and something to hope for."
- Joseph Addison
Nov 12 '05 #3
ph*@cs.dal.ca wrote:
Hi,

I think a lot of that would be proprietory (sp?) information. However,
if you search google for "db2 internals", you will see that there
are occasional presentations given.

I also think that some information about the page layout is also
discussed in the online documentation (e.g. Performance). I don't think
you will find anything on migration or chaining, however.

Good luck :)
Bill

hopehope_123 <ho**********@yahoo.com> wrote:
Hi ,


Where can i find information about db2 block structure? I want to know
how it stores rows into blocks , how it handles issues such as row
migration / chaining or etc.

Kind Regards,
hope

Matter of fact IBM provides dosumentation of the physical layout upon
request. This is mostly used by tool-vendors providing custom LOAD
utilities.

Cheers
Serge

Nov 12 '05 #4
Serge Rielau wrote:
Matter of fact IBM provides dosumentation of the physical layout upon
request. This is mostly used by tool-vendors providing custom LOAD
utilities.


One can also derive some of the information from the DB2 logs where the
placement of records on a page and free space information are tracked.

--
Knut Stolze
Information Integration
IBM Germany / University of Jena
Nov 12 '05 #5

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