[Systems] caching disabled by *.sl.o

Sascha Silbe sascha-ml-ui-sugar-systems at silbe.org
Thu Oct 1 17:28:16 EDT 2009


While configuring and testing squid on my new server I noticed most SL 
web services disable or prevent caching from working, thereby severly 
degrading performance and increasing bandwidth usage (both on server and 
client side):


Explicitly disabled:

Expires: Thu, 01 Jan 1970 00:00:00 GMT
Cache-Control: private, must-revalidate, max-age=0

It's setting Vary properly, so disabling caching has no positive effect 
(other than maybe for some broken browser) that I'm aware of.


For Trac it's slightly "better", as it only sets must-revalidate (but 
without giving Expires or max-age, so behaviour isn't strictly defined). 
But since it doesn't support If-Modified-Since (even on single tickets), 
the result is the same (the whole page always gets fully refetched).


Not cached when using default squid settings because Last-Modified (LM) 
is not given. Does not support If-Modified-Since (IMS).


(Currently unreachable via IPv6)

Does two redirections for start page (/ -> /en-US/ -> /en-US/sugar/), 
both times with caching disabled and probably incomplete Vary header 
(only gives Accept-Encoding, nothing language-related).
Remaining pages: Not cached when using default squid settings because LM 
is not given. Does not support IMS.


Works fine. Amazingly fast. :-P


Explicitly disabled (even for static data like commits):

Cache-Control: private, max-age=0, must-revalidate

Vary not set, no LM, IMS not supported.


Explicitly disabled:

Cache-Control: private, pre-check=0, post-check=0, max-age=0
Pragma: no-cache

Vary not set, no LM, IMS not supported.


Directories: Vary set, but no LM and no IMS.
Files: OK (tested using wget+squid).


Explicitly disabled for main page:

Cache-control: no-cache

Seems fine otherwise, esp. archives.

remaining services

Not tested because I got tired.

Test method

All tests done using telnet, giving only HEAD request and Host header 
(optionally If-Modified-Since) given. => Nothing that would have matched 
Requested the usual HTML, not images or tarballs unless explicitly 

CU Sascha

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