Defective Semantics » apache http://scarff.id.au Dean Scarff's perpetual struggle with technology, and other anecdotes Thu, 03 Nov 2011 22:39:55 +0000 en hourly 1 http://wordpress.org/?v=3.2.1 Apache 304 and mod_deflate revisited http://scarff.id.au/blog/2009/apache-304-and-mod_deflate-revisited/ http://scarff.id.au/blog/2009/apache-304-and-mod_deflate-revisited/#comments Thu, 09 Jul 2009 03:51:42 +0000 Dean http://scarff.id.au/?p=290 Last year I commented on how mod_deflate breaks the cache validation model. Essentially the problem has been addressing two issues:

  • Apache bug #39727, RFC 2616 requires unique strong entity tags for every entity. Presumably this means after Content-Encoding (but not Transfer-Encoding). The fix was for deflate to add “-gzip” to the ETag.
  • Apache bug #45023 concerns Apache not being able to recognise the transformed ETag (with the -gzip) as the same entity, and hence not sending 304s when it should have.

So in January 2008, a change was committed to fix #39727, which introduced #45023. Now in April this year, it was reversed to fix #45023. I agree with the priorities here; no caching is much worse for web performance.

As Roy Fielding pointed out the correct way to deal with this issue is to stop abusing Content-Encoding for performance-compression and start using Transfer-Encoding; pity browsers and HTTP… more

]]> Last year I commented on how mod_deflate breaks the cache validation model. Essentially the problem has been addressing two issues:

So in January 2008, a change was committed to fix #39727, which introduced #45023. Now in April this year, it was reversed to fix #45023. I agree with the priorities here; no caching is much worse for web performance.

As Roy Fielding pointed out the correct way to deal with this issue is to stop abusing Content-Encoding for performance-compression and start using Transfer-Encoding; pity browsers and HTTP servers haven’t got there yet.

]]> http://scarff.id.au/blog/2009/apache-304-and-mod_deflate-revisited/feed/ 0 Apache 304s and mod_deflate http://scarff.id.au/blog/2008/apache-304s-and-mod_deflate/ http://scarff.id.au/blog/2008/apache-304s-and-mod_deflate/#comments Sat, 21 Jun 2008 12:18:59 +0000 Dean http://scarff.id.au/?p=39 The deflate output filter in Apache breaks Apache’s handling of the HTTP cache validation model. It won’t send an HTTP 304 status if mod_deflate is actively filtering the response, even if the Etag and Last-Modified allow it to. I asked, and apparently this is a known issue. I might have to wait until after exams before making a patch for this one.

In its current state, this introduces a tradeoff for large, uncompressed static files (like CSS and Javascript):

  • gzip stuff, and you improve site performance the first time someone visits, but it never gets any faster.
  • allow Apache to send 304 statuses, let the user have a slow load on their first visit, but celebrate as they hit their cache thereafter

The second option looks more attractive.

]]> The deflate output filter in Apache breaks Apache’s handling of the HTTP cache validation model. It won’t send an HTTP 304 status if mod_deflate is actively filtering the response, even if the Etag and Last-Modified allow it to. I asked, and apparently this is a known issue. I might have to wait until after exams before making a patch for this one.

In its current state, this introduces a tradeoff for large, uncompressed static files (like CSS and Javascript):

  • gzip stuff, and you improve site performance the first time someone visits, but it never gets any faster.
  • allow Apache to send 304 statuses, let the user have a slow load on their first visit, but celebrate as they hit their cache thereafter

The second option looks more attractive.

]]> http://scarff.id.au/blog/2008/apache-304s-and-mod_deflate/feed/ 0