IDS Forum

RE: alter table: 'lost' extents

Posted By: Sebastian, Norma J.
Date: Friday, 6 August 2004, at 7:53 a.m.

In Response To: AW: alter table: 'lost' extents (Alexey Sonkin )

Alexey,
What hardware o/s are you on?
I'm heading for infx 9.3, then 9.4, and hope not to hit this if this is
for real. I'm on sun solaris 2.9.
Thanks,
Norma Jean


-----Original Message-----
From: forum.subscriber@iiug.org [mailto:forum.subscriber@iiug.org] On
Behalf Of Alexey Sonkin
Sent: Thursday, August 05, 2004 9:52 PM
To: ids@iiug.org
Subject: AW: alter table: 'lost' extents [3327]

I've just made some deeper investigation.

One of extents (I took the largest for simplicity) reported by chunk's
extent list (oncheck -pe) as belonging to the dropped table is also not
reflected in the "Chunk free list"
(the third page of any non-root chunk, can be displayed with 'oncheck
-pP CHUNK_NUM 2', and recursively with 'oncheck -pP CHUNK_NUM NEXT'
where NEXT is displaeyed in the 'next'
field of the page header in the previous output; NEXT=0 means last page
in a linked list) That means, the this extent will never be re-used by
the engine.
It's lost forever.

The conclusion is:

Informix is not releasing 'old' (previous version) extents after table
subjected to 'in-place-alter-table' is dropped !!!!!!!!!!!!!!

I'll try to wait for response from the 'list' for a few days and file a
bug to PA.

P.S.
I converted my 9.21 DEV database to 9.40 and repeated the experiment.
No change. Lost space again.

THIS IS A REALLY BAD PROBLEM

------------------------------------------
Alexey Sonkin


-----Original Message-----
From: Alexey Sonkin [mailto:alexeis@grandvirtual.com]


Hi, everybody,

I've just found a very unpleasant problem with 9.21uc4

I have a huge table that was altered (column added) when it was big
enough.
'Alter table' was 'in-place' - just because the operation went very
fast.
After that, a lot of inserts were made, and old records were not
updated.

Later, the table was dropped.

When I made an analysis of disk extents with 'oncheck -pe', I was
surprised:
a lot of extents (actually, containing all the 'before alter table'
records) were not released by the 'drop table'!!!

Is it a known bug?
Is it fixed in 9.40?
Is there way to return extents to the free page pool?

------------------------------------------
Alexey Sonkin

sending to informix-list


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Messages In This Thread

• AW: alter table: 'lost' extents
  Alexey Sonkin -- Thursday, 5 August 2004, at 10:51 p.m.
  • RE: alter table: 'lost' extents
    Sebastian, Norma J. -- Friday, 6 August 2004, at 7:53 a.m.

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