1VMOD_XKEY(3) VMOD_XKEY(3)
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6 vmod_xkey - Surrogate keys support for Varnish Cache
7
9 import xkey [as name] [from "path"]
10 INT purge(STRING keys)
12 INT softpurge(STRING keys)
14
16 This vmod adds secondary hashes to objects, allowing fast purging on
17 all objects with this hash key.
18 You can use this to indicate relationships, a bit like a "tag". Then
20 clear out all object that have this tag set. Two good use cases are
21 news sites, where one might add all the stories mentioned on a particu‐
22 lar page by article ID, letting each article referenced create an xkey
23 header.
24 Similarly with an e-commerce site, where various SKUs are often refer‐
26 enced on a page.
27 Hash keys are specified in the xkey response header. Multiple keys can
29 be specified per header line with spaces and/or commas as separators.
30 Alternatively, they can be specified in multiple xkey response headers.
31 Preferably the secondary hash keys are set from the backend applica‐
33 tion, but the header can also be set from VCL in vcl_backend_response.
34 VCL example:
36 vcl 4.0;
38 import xkey;
39 backend default { .host = "192.0.2.11"; .port = "8080"; }
41 acl purgers {
43 "203.0.113.0"/24;
44 }
45 sub vcl_recv {
47 if (req.method == "PURGE") {
48 if (client.ip !~ purgers) {
49 return (synth(403, "Forbidden"));
50 }
51 if (req.http.xkey) {
52 set req.http.n-gone = xkey.purge(req.http.xkey);
53 # or: set req.http.n-gone = xkey.softpurge(req.http.xkey)
54 return (synth(200, "Invalidated "+req.http.n-gone+" objects"));
56 } else {
57 return (purge);
58 }
59 }
60 }
61 Example
63 On an e-commerce site we have the backend application issue an xkey
64 header for every product that is referenced on that page. So the header
65 for a certain page might look like this:
66 HTTP/1.1 OK
68 Server: Apache/2.2.15
69 xkey: 8155054
70 xkey: 166412
71 xkey: 234323
72 Alternatively you may instead use a single header with space separated
74 values like xkey: 8155054 166412 234323.
75 This requires a bit of VCL to be in place. The VCL can be found above.
77 Then, in order to keep the web in sync with the database, a trigger is
79 set up in the database. When an SKU is updated this will trigger an
80 HTTP request towards the Varnish server, clearing out every object with
81 the matching xkey header:
82 PURGE / HTTP/1.1
84 Host: www.example.com
85 xkey: 166412
86 Several xkey-purge headers are also supported like in the response ex‐
88 ample above, and you may also here use a single header with space
89 seperated values like xkey-purge: 166412 234323.
90 Unlike xkey header for responses, purge header is fully configurable by
92 means of adjusting the name of the header in the VCL example above.
93 Note the xkey header. It is probably a good idea to protect this with
95 an ACL so random people from the Internet cannot purge your cache.
96 Varnish will find the objects and clear them out, responding with:
98 HTTP/1.1 200 Purged
100 Date: Thu, 24 Apr 2014 17:08:28 GMT
101 X-Varnish: 1990228115
102 Via: 1.1 Varnish
103 The objects are now cleared.
105 INT purge(STRING keys)
107 Description
108 Purges all objects hashed on any key found in the keys argument.
109 Returns the number of objects that were purged.
110 The keys may contain a list of space-separated ids.
112 INT softpurge(STRING keys)
114 Description
115 Performs a "soft purge" for all objects hashed on any key found
116 in the keys argument. Returns the number of objects that were
117 purged.
118 A softpurge differs from a regular purge in that it resets an
120 object's TTL but keeps it available for grace mode and condi‐
121 tional requests for the remainder of its configured grace and
122 keep time.
123 Counters
125 #
126 varnish_vsc_begin:: xkey
127
129 Metrics from vmod_xkey
130 g_keys – gauge - info
132 Number of surrogate keys
133 Number of surrogate keys in use. Increases after a request that in‐
135 cludes a new key in the xkey header. Decreases when a key is purged
136 or when all cache objects associated with a key expire.
137 g_hashhead_bytes – gauge - debug
139 Bytes used by all xkey_hashhead objects
140 Total bytes used by hashhead objects. Tracks linearly with the num‐
142 ber of surrogate keys in use.
143 g_ochead_bytes – gauge - debug
145 Bytes used by all xkey_ochead objects
146 Total bytes used by ochead objects. Increases when an object is
148 added to a key or a key is added to an object. Decreases when the
149 relationship is removed.
150 g_oc_bytes – gauge - debug
152 Bytes used by all xkey_oc objects
153 Total bytes used by oc objects. Tracks linearly with the number of
155 cached objects that are referenced by surrogate keys.
156 g_bytes – gauge - info
158 Bytes used by xkeys
159 Current number of bytes used by xkeys and their references to the
161 object cache.
162 VMOD_XKEY(3)