[This is preliminary documentation and subject to change]

# Enabling HTTP Compression

HTTP compression provides faster transmission of pages between the Web server and compression-enabled browsers. If your server generates a large volume of dynamic content, consider whether the additional processing cost of HTTP compression is one that you can reasonably afford. If the % Processor Time is already 80 percent or higher, enabling HTTP compression is not recommended.

To test HTTP compression

1. Use System Monitor to log the % Processor Time counter of the Processor object over several days to establish a baseline. This counter has a Total instance, and a separate instance for each processor in the system. (If your server has more than one processor, you should probably watch the individual processors as well as the total, to discover any imbalance in the workload.) As an adjunct, you should probably also log the Bytes Sent/sec counter of the Network Interface object.
2. Enable compression and continue to log the value of these counters for an extended period, preferably for several days, so you have a good basis for comparison.
3. Compare the values without and with compression.

Note If you see signs of blocking or bottlenecking during the test, you should promptly stop the test. A significant drop in the value of either counter indicates that performance with compression enabled has decreased when compared to performance without compression enabled.

To enable HTTP compression

1. In the IIS snap-in, right-click the computer icon, and select Properties to display its property sheets.
2. On the Internet Information Services tab, select WWW Service under Master Properties.
3. Click Edit.
4. On the Service property sheet, select Compress static files to compress only static files for transmission to compression-enabled clients.
5. To compress application files, select Compress application files.
6. Type the path to a local directory in the Temporary folder box, or use the Browse button to locate a directory where compressed files will be kept.

   Note The directory must be on a local drive and it must be on an NTFS partition. The directory, which should not be shared, cannot be a compressed directory.

7. Set the maximum size to allow for the folder to either Unlimited, or limit the size by typing a number in the Limited to text box.

Related Topics

- For more information about compression issues, see About Network Capacity Planning.
- For a list of counters provided by IIS, see Counters Reference.
- For a list of all timeout values that can be set by IIS, see Timeouts Reference.

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