Home / server / Questions / 372290
Accepted
THpubs
Asked: 2012-03-22 22:28:07 +0800 CST

Why am I getting a low cach hit rate average in Varnish?

  • 772

Any one know why we are getting a very low cache hit rate average when using Wordpress (With Varnish and Nginx)?

Varnish stat shows :

Hitrate ratio: 10 100 518 Hitrate avg: 0.4143 0.2690 0.1948

Any idea how to fix this? My varnish default.vcl is :

# This is a basic VCL configuration file for varnish.  See the vcl(7)
# man page for details on VCL syntax and semantics.
#
# Default backend definition.  Set this to point to your content
# server.
#
backend default {
    .host = "77.81.240.177";
    .port = "8080";
}

acl purge {
    "77.81.240.177";
}

sub vcl_recv {

    # Add a unique header containing the client address
    remove req.http.X-Forwarded-For;
    #set    req.http.X-Forwarded-For = client.ip;
    set    req.http.X-Forwarded-For = req.http.rlnclientipaddr;    

    # Let's make sure we aren't compressing already compressed formats.
    if (req.http.Accept-Encoding) {
        if (req.url ~ "\.(jpg|png|gif|gz|tgz|bz2|mp3|mp4|m4v)(\?.*|)$") {
            remove req.http.Accept-Encoding;
        } elsif (req.http.Accept-Encoding ~ "gzip") {
            set req.http.Accept-Encoding = "gzip";
        } elsif (req.http.Accept-Encoding ~ "deflate") {
            set req.http.Accept-Encoding = "deflate";
        } else {
            remove req.http.Accept-Encoding;
        }
    }

    if (req.request == "PURGE") {
        if (!client.ip ~ purge) {
            error 405 "Not allowed.";
        }
        return(lookup);
    }

    if (req.url ~ "^/$") {
        unset req.http.cookie;
    }
}

sub vcl_hit {
    if (req.request == "PURGE") {
        set obj.ttl = 0s;
        error 200 "Purged.";
    }
}

sub vcl_miss {
    if (req.request == "PURGE") {
        error 404 "Not in cache.";
    }

    if (!(req.url ~ "wp-(login|admin)")) {
        unset req.http.cookie;
    }

    if (req.url ~ "^/[^?]+.(jpeg|jpg|png|gif|ico|js|css|txt|gz|zip|lzma|bz2|tgz|tbz|html|htm)(\?.|)$") {
        unset req.http.cookie;
        set req.url = regsub(req.url, "\?.$", "");
    }

    if (req.url ~ "^/$") {
        unset req.http.cookie;
    }
}

sub vcl_fetch {
    if (req.url ~ "^/$") {
        unset beresp.http.set-cookie;
    }

    if (!(req.url ~ "wp-(login|admin)")) {
        unset beresp.http.set-cookie;
    }

    if (req.url ~ "^/w00tw00t") {
        error 403 "Not permitted";
    }
}
wordpress varnish

2 Answers

  1. Best Answer

    A good approach is to inspect the traffic with varnishlog in order to see what makes which rules apply.

    Since you're not enforcing a TTL, my guess is that the wordpress site delivers Cache-Control headers like "max-age: 0", or "no-cache" "private" or something, and varnish honors such headers unless you specifically tell it not to, i.e:

     sub vcl_fetch {
     if (!(req.url ~ "wp-(login|admin)")) {
         unset beresp.http.set-cookie;
         set beresp.ttl = 3600s;
     }

    First rule in vcl_fetch does not make sense, as second rule will unset all set-cookies for all urls but wp-login/wp-admin.


    Add some config to vcl_deliver to output headers that states if it's a hit or not:

    sub vcl_deliver {
        if (obj.hits > 0) {
                set resp.http.X-Cache = "HIT";
        } else {
                set resp.http.X-Cache = "MISS";
        }
     return (deliver);
}

    Other feedback to you config:

    In vcl_recv, you do "unset req.http.cookie" if url is not wp-login or wp-admin, which means that if a user logs on /wp-login then goes to "/", you will unset his cookie. You only need to unset cookies in vcl_recv for urls that shouldn't ever need one, ie .(js|css|png|jpg) etc, and instead remove the set-cookie in vcl_fetch.

    • 4

  2. wp-varnish

    Checkout wp-varnish - A plugin for WordPress that will purge content in Varnish when content in WordPress is changed. It also comes with a sample VCL which should give you a better hitrate

    Sample VCL

    backend default {
  .host = "127.0.0.1";
  .port = "8080";
}

acl purge {
  "localhost";
}

sub vcl_recv {
  if (req.request == "PURGE") {
    if(!client.ip ~ purge) {
      error 405 "Not allowed.";
    }
    return(lookup);
  }

  if (req.request != "GET" &&
      req.request != "HEAD" &&
      req.request != "PUT" &&
      req.request != "POST" &&
      req.request != "TRACE" &&
      req.request != "OPTIONS" &&
      req.request != "DELETE") {
    return (pipe);
  }

  if (req.request != "GET" && req.request != "HEAD") {
    return (pass);
  }

  if (req.url ~ "wp-(login|admin)" || req.url ~ "preview=true") {
    return (pass);
  }

  remove req.http.cookie;
  return (lookup);
}

sub vcl_hit {
  if (req.request == "PURGE") {
    purge;
    error 200 "Purged.";
  }
}

sub vcl_miss {
  if (req.request == "PURGE") {
    purge;
    error 200 "Purged.";
  }
}

sub vcl_fetch {
  if (req.url ~ "wp-(login|admin)" || req.url ~ "preview=true") {
    return (hit_for_pass);
  }

  set beresp.ttl = 24h;
  return (deliver);
}
    • 2