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The DHCP database

Updated: January 21, 2005

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

The DHCP database

There is no set limit to the number of records that a DHCP server can store. The size of the database is dependent upon the number of DHCP clients on the network. The DHCP database grows over time as a result of clients starting and stopping on the network.

The size of the DHCP database is not directly proportional to the number of active client lease entries. Over time, as some DHCP client entries become obsolete and are deleted, there remains some unused space.

To recover the unused space, the DHCP database is compacted. Starting with Windows NT Server 4.0, dynamic database compaction occurs on DHCP servers as an automatic background process during idle time or after a database update.


  • When using or upgrading DHCP databases used with earlier versions of Windows NT Server, the DHCP database requires conversion. In the Windows Server 2003 family, if a previous copy of the DHCP server database is detected during an upgrade, it is automatically converted to the current database version and format. For larger databases, this process can increase the time needed to complete the installation.

DHCP database files

The DHCP server database in Windows Server 2003 family uses the Exchange Server JET storage engine. When you install the DHCP service, the files shown in the following table are automatically created in the Systemroot\System32\Dhcp directory.

DHCP service database files


File Description


The DHCP server database file.


A temporary file used by the DHCP database as a swap file during database index maintenance operations. This file sometimes remains in the Systemroot\System32\Dhcp directory after a system failure.

J50.log and J50#####.log

A log of all database transactions. This file is used by the DHCP database to recover data when necessary.


A checkpoint file.


  • The J50.log file, J50#####.log file, Dhcp.mdb file, and Dhcp.tmp file should not be removed or altered.

The DHCP server database is a dynamic database that is updated as DHCP clients are assigned or as they release their TCP/IP configuration parameters. Because the DHCP database is not a distributed database like the WINS server database, maintaining the DHCP server database is less complex.

The DHCP database and related registry entries are automatically backed up at a specific interval (60 minutes by installation default). You can change this installation default by changing the value of BackupInterval in the following registry key:



  • Incorrectly editing the registry may severely damage your system. Before making changes to the registry, you should back up any valued data on the computer.

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