• Posts
  • RSS
  • ◂◂RSS
  • Contact

  • Apache doesn't cache htaccess configs

    February 5th, 2013
    tech  [html]
    When I previously suggested that Apache improve performance on .htaccess files by caching them and then watching for changes with inotify, Chris wrote:
    just invalidate its cache
    This is very sensible, except Apache doesn't actually cache .htaccess files between requests.

    Apache checks .htaccess files in a monster function, ap_directory_walk. It's called on every request, and if AllowOverride is set it will call ap_parse_htaccess on every directory from the root out to the leaf. In ap_parse_htaccess you can see that it does have a per-request cache for parsed .htaccess files:

        /* firstly, search cache */
        for (cache = r->htaccess; cache != NULL; cache = cache->next) {
            if (cache->override == override && strcmp(cache->dir, d) == 0) {
                *result = cache->htaccess;
                return OK;
            }
        }
    
        ... more sanity and safety checks ...
    
        dc = ap_create_per_dir_config(r->pool);
    
        ... load and parse the htaccess file into dc ...
    
        /* cache it */
        new = apr_palloc(r->pool, sizeof(struct htaccess_result));
        new->dir = parms.path;
        new->override = override;
        new->override_opts = override_opts;
        new->htaccess = dc;
    
        /* add to head of list */
        new->next = r->htaccess;
        r->htaccess = new;
    
        return OK;
    

    Now it may be that the overhead of parsing .htaccess files just isn't that big and that in many cases a cache would just be a waste of memory. While I doubt that, this is testable. To get a best-case for caching we could test just something like:

       /var/www/foo.html
       /var/www/.htaccess
    
    Comparing this to the version that has the configuration options in a <Directory> block should tell us the maximum we could expect to gain from caching.

    Update 2013-02-08: I ran some tests on the above configuration with ab, but the variance was so extreme (some runs of 10k requests averaged 4k/s while others averaged 500/s) that I think something else is wrong. I tried running longer tests with more requests but ab consistently died with apr_socket_recv: Operation timed out (60) before finishing the test.

    Comment via: google plus, facebook

    Recent posts on blogs I like:

    Collections: The Queen’s Latin or Who Were the Romans? Part IV: The Color of Purple

    This is the fourth part (I, II, III) of our series asking the question “Who were the Romans?” and contrasting the answer we get from the historical evidence with the pop-cultural image of the Romans as a culturally and ethnically homogeneous society typic…

    via A Collection of Unmitigated Pedantry July 23, 2021

    The Leakage Problem

    I’ve spent more than ten years talking about the cost of construction of physical infrastructure, starting with subways and then branching on to other things, most. And yet there’s a problem of comparable size when discussing infrastructure waste, which, …

    via Pedestrian Observations July 23, 2021

    Songs about terrible relationships

    [Spoilers for several old musicals.] TV Tropes lists dozens of examples of the “I want” song (where the hero of a musical sings about their dream of escaping their small surroundings). After watching a bunch of musicals on maternity leave, I’m wondering h…

    via The whole sky July 17, 2021

    more     (via openring)


  • Posts
  • RSS
  • ◂◂RSS
  • Contact