Compressing xls content with apache deflate module

I am trying to compress an excel spreadsheet being sent from my application using apache deflate module. I have added the following line to the my sites-enabled file:

AddOutputFilterByType DEFLATE text/html text/plain text/xml text/css text/javascript application/excel

But is seems to make the response data bigger???

Using firebug, without the module I downloaded the xls spreadsheet from the application and it downloaded 100Kb of data, the file size once on the filesystem was also 100Kb as expected. Once I enabled the deflate module as described above and repeated the process, the amount of da开发者_运维百科ta downloaded was 295Kb?? but the file was still only 100Kb once save on the filesystem.

As an experiment I manually gzipped the saved xls file and it compressed to 20Kb.

What am I doing wrong here?

Using deflate (Firebug output):

200 OK   xxxxxxx.co.za   293 KB

4.43s 
ParamsHeadersPostPutResponseCacheHTML
Response Headers 
Date    Tue, 03 Nov 2009 13:01:43 GMT 
Server  Apache/2.2.4 (Ubuntu) mod_jk/1.2.23 PHP/5.2.3-1ubuntu6.4 mod_ssl/2.2.4 OpenSSL/0.9.8e
Content-Disposition attachment; filename="Employee List.xls"
Vary    Accept-Encoding
Content-Encoding    gzip
Content-Type    application/excel

Without deflate (Firebug output):

200 OK     xxxxxxxx.co.za   100 KB

3.46s
ParamsHeadersPostPutResponseCacheHTML
Response Headers
Date    Tue, 03 Nov 2009 13:06:00 GMT
Server  Apache/2.2.4 (Ubuntu) mod_jk/1.2.23 PHP/5.2.3-1ubuntu6.4 mod_ssl/2.2.4 OpenSSL/0.9.8e
Content-Disposition attachment; filename="Employee List.xls"
Content-Length  102912
Content-Type    application/excel

Try forcing the highest compression level and ensure that other directives affecting compression ratios have sensible values (see mod_deflate reference for more info):

DeflateCompressionLevel 9
DeflateBufferSize 8096
DeflateMemLevel 9
DeflateWindowSize 15

Also according to IANA, the MS Excel content type should be application/vnd.ms-excel, and this is also what my installation Apache/2.2.8 (Ubuntu) returns when asked for an xls file. So it's a bit weird that your Apache doesn't behave similarly. Does the same thing happen for any xls file? If not, there could be something wrong with the particular file.

This is a bit long shot, but what happens if you add application/vnd.ms-excel to the AddOutputFilterByType list?