Compressing and Uncompressing Files Cause File Cache to Grow

ID: Q164260

The information in this article applies to:

Microsoft Windows NT Workstation version 4.0
Microsoft Windows NT Server version 4.0

SYMPTOMS

When you compress or uncompress big files, the performance of the interactive processes may suffer. This happens when the files are bigger than the physical memory of the computer.

All three of the following utilities capable of compressing or uncompressing files in Windows NT show this behavior:

COMPACT utility (Compact.exe)
File Manager (Winfile.exe)
Windows NT Explorer (Explorer.exe)

When you run performance monitor during compression you will see that the cache (Memory: Cache Bytes) is very large (between 50 and 90 percent of the physical memory) and the working sets of the processes (Process: Working Set, Instance _Total) are reduced.

MORE INFORMATION

The CreateFile API has a flag FILE_FLAG_SEQUENTIAL_SCAN that is especially useful when working on files in a sequential manner. It tells Cache Manager not to grow the file cache when requests for this handle arrive. Therefore, Memory Manager does not have to shrink the application's working set to accommodate the bigger cache.

None of the three utilities used this flag when opening the files for compression or decompression.

STATUS

Microsoft has confirmed this to be a problem in Windows NT version 4.0. This problem was corrected in the latest Microsoft Windows NT 4.0 U.S. Service Pack. For information on obtaining the service pack, query on the following word in the Microsoft Knowledge Base (without the spaces):

S E R V P A C K

Additional query words: prodnt virtual memory

Keywords : kbbug4.00 kbfix4.00 kbfix4.00.sp3 NTSrvWkst ntutil
Version : 4.0
Platform : winnt
Issue type : kbbug