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Q197632: Registry Hive Fragmentation Leads to Excessive Size

Article: Q197632
Product(s): Microsoft Windows NT
Version(s): winnt:4.0
Operating System(s): 
Keyword(s): kbWinNT400sp5fix
Last Modified: 16-MAY-2002

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The information in this article applies to:

- Microsoft Windows NT Workstation version 4.0 
- Microsoft Windows NT Server version 4.0 
- Microsoft Windows NT Server, Enterprise Edition version 4.0 
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SYMPTOMS
========

Processes that use the registry to repeatedly modify the same values in small
increments can cause excessive memory fragmentation in the corresponding
registry hive. The sum of the fragmented cells can become so large that the hive
size winds up many times larger than the sum of actual data in the hive.
Eventually, the sum of the hive will exceed the Registry Size Limit (RSL),
causing subsequent modifications to fail until the RSL is increased. As an
example consider the SAM hive used to store Windows NT accounts. The SAM size
frequently exceeds projected sizes due to the fact that it fragments the SAM
hive when adding members to large groups.

CAUSE
=====

In the SAM example, when a user is added to a large group it causes the registry
value for that group to be replaced and the old value added to a hash of free
lists by size of allocation. The freed cell is coalesced with the nearest
neighbor cell in memory, if it's a free cell, to create a slightly larger cell
to add to the free lists. Over several additions, the free lists can contain
several cells that are never used because they're too small. Over time the sum
of the free cells become so large that the sum of the hives exceeds RSL.

RESOLUTION
==========

To resolve this problem, obtain the latest service pack for Windows NT 4.0 or
the individual software update. For information on obtaining the latest service
pack, please go to:

- http://www.microsoft.com/Windows/ServicePacks/

-or-

- Q152734 How to Obtain the Latest Windows NT 4.0 Service Pack

For information on obtaining the individual software update, contact Microsoft
Product Support Services. For a complete list of Microsoft Product Support
Services phone numbers and information on support costs, please go to the
following address on the World Wide Web:

  http://support.microsoft.com/default.aspx?scid=fh;EN-US;CNTACTMS



STATUS
======

Microsoft has confirmed this to be a problem in Windows NT version 4.0. This
problem was first corrected in Windows NT version 4.0 Service Pack 5.

Additional query words: 4.00

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Keywords          : kbWinNT400sp5fix 
Technology        : kbWinNTsearch kbWinNTWsearch kbWinNTW400 kbWinNTW400search kbWinNT400search kbWinNTSsearch kbWinNTSEntSearch kbWinNTSEnt400 kbWinNTS400search kbWinNTS400
Version           : winnt:4.0
Hardware          : ALPHA x86
Issue type        : kbbug
Solution Type     : kbfix

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