I recently had the partition that contains my cache/compress directory become full. After that, each time a request was handled for a file that didn't already appear in the compressed cache, an error like the following was logged:
2007-04-25 09:58:47: (mod_compress.c.398) creating cachefile /tmp/cache/compress/stargaze/ILmass.htm-gzip-2289252-13601-1116618996 failed No space left on device
This was all fine, and the request was served with un-cached content, as you would expect. However, the next time that page was requested, the empty cache file would be found, and the request would be fulfilled with a zero-length response. I served a number of empty pages that day before I noticed.
The solution is simply to remove the compressed cache file if the write fails. A patch is attached.