when does DB2 do a page reorg- Z/OS DB2

Ramachandran Subramanian

when does DB2 do a page reorg- Z/OS DB2
I have heard that DB2 some times moves around pages
and does some internal reorgs of pages. Is this true ?
If so , when and how does it do that. Can some one
explain to me in a way a newbie can understand.

Thank you

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Walter Janißen

Re: when does DB2 do a page reorg- Z/OS DB2
(in response to Ramachandran Subramanian)
Hi

I never heard about that. The only thing I know about and what has
something do with internal reorg of pages, is, that, if you insert rows
near the end of the tablespaces, then a certain number of pages will be
preformatted asynchronously.

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Mike Turner

Re: when does DB2 do a page reorg- Z/OS DB2
(in response to Walter Janißen)
Hi

Some notes:

After a row is deleted from a page the space occupied by the row and the ID
map slot both become free. DB2 does not move the remaining rows to the front
of the page.

The page header points to both the area of contiguous free space at the end
of the page and also to the first 'big hole' (an area of free space >= 5
bytes) in the page.

Big holes are chained together by their headers.

Small holes (areas of free space < 5 bytes) are not chained together and are
only recovered when the page is compacted.

If a new row is to be inserted into a page and there is enough contiguous
free space, either at the end or in a single big hole, the row is inserted
in the available space. If there is not enough contiguous free space but
there IS enough total free space, then the page is compacted and all big and
small holes will be merged into the contiguous free space at the end of the
page.

Free ID map entries are chained from the first entry.

Regards
Mike Turner
Email: [login to unmask email]
Tel: +44 (0)1565 873702
web: www.michael-turner.ltd.uk

-----Original Message-----
From: [login to unmask email]
[mailto:[login to unmask email]On Behalf Of Ramachandran
Subramanian
Sent: Tuesday, 21 December 2004 07:30
To: [login to unmask email]
Subject: when does DB2 do a page reorg- Z/OS DB2



I have heard that DB2 some times moves around pages
and does some internal reorgs of pages. Is this true ?
If so , when and how does it do that. Can some one
explain to me in a way a newbie can understand.

Thank you

__________________________________________________
Do You Yahoo!?
Tired of spam? Yahoo! Mail has the best spam protection around
http://mail.yahoo.com

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