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VMOD_XKEY(3) Library Functions Manual VMOD_XKEY(3) NAME vmod_xkey - Surrogate keys support for Varnish Cache SYNOPSIS import xkey [as name] [from "path"] INT purge(STRING keys) INT softpurge(STRING keys) DESCRIPTION PLEASE NOTE that this VMOD is currently in maintenance mode and has known performance issues, particularly regarding scalability, which will not be addressed in this implementation. For a more robust solu- tion with proven scalability, improved syntax support, and proper soft- purge functionality, consider using yKey, included in Varnish Enter- prise. This vmod adds secondary hashes to objects, allowing fast purging on all objects with this hash key. You can use this to indicate relationships, a bit like a "tag". Then clear out all object that have this tag set. Two good use cases are news sites, where one might add all the stories mentioned on a particu- lar page by article ID, letting each article referenced create an xkey header. Similarly with an e-commerce site, where various SKUs are often refer- enced on a page. Hash keys are specified in the xkey response header. Multiple keys can be specified per header line with spaces and/or commas as separators. Alternatively, they can be specified in multiple xkey response headers. Preferably the secondary hash keys are set from the backend applica- tion, but the header can also be set from VCL in vcl_backend_response. VCL example: vcl 4.0; import xkey; backend default { .host = "192.0.2.11"; .port = "8080"; } acl purgers { "203.0.113.0"/24; } sub vcl_recv { if (req.method == "PURGE") { if (client.ip !~ purgers) { return (synth(403, "Forbidden")); } if (req.http.xkey) { set req.http.n-gone = xkey.purge(req.http.xkey); # or: set req.http.n-gone = xkey.softpurge(req.http.xkey) return (synth(200, "Invalidated "+req.http.n-gone+" objects")); } else { return (purge); } } } Example On an e-commerce site we have the backend application issue an xkey header for every product that is referenced on that page. So the header for a certain page might look like this: HTTP/1.1 OK Server: Apache/2.2.15 xkey: 8155054 xkey: 166412 xkey: 234323 Alternatively you may instead use a single header with space separated values like xkey: 8155054 166412 234323. This requires a bit of VCL to be in place. The VCL can be found above. Then, in order to keep the web in sync with the database, a trigger is set up in the database. When an SKU is updated this will trigger an HTTP request towards the Varnish server, clearing out every object with the matching xkey header: PURGE / HTTP/1.1 Host: www.example.com xkey: 166412 Several xkey-purge headers are also supported like in the response ex- ample above, and you may also here use a single header with space seperated values like xkey-purge: 166412 234323. Unlike xkey header for responses, purge header is fully configurable by means of adjusting the name of the header in the VCL example above. Note the xkey header. It is probably a good idea to protect this with an ACL so random people from the Internet cannot purge your cache. Varnish will find the objects and clear them out, responding with: HTTP/1.1 200 Purged Date: Thu, 24 Apr 2014 17:08:28 GMT X-Varnish: 1990228115 Via: 1.1 Varnish The objects are now cleared. INT purge(STRING keys) Description Purges all objects hashed on any key found in the keys argument. Returns the number of objects that were purged. The keys may contain a list of space-separated ids. INT softpurge(STRING keys) Description Performs a "soft purge" for all objects hashed on any key found in the keys argument. Returns the number of objects that were purged. A softpurge differs from a regular purge in that it resets an object's TTL but keeps it available for grace mode and condi- tional requests for the remainder of its configured grace and keep time. Counters # varnish_vsc_begin:: xkey XKEY XKEY COUNTERS Metrics from vmod_xkey g_keys gauge - info Number of surrogate keys Number of surrogate keys in use. Increases after a request that in- cludes a new key in the xkey header. Decreases when a key is purged or when all cache objects associated with a key expire. g_hashhead_bytes gauge - debug Bytes used by all xkey_hashhead objects Total bytes used by hashhead objects. Tracks linearly with the num- ber of surrogate keys in use. g_ochead_bytes gauge - debug Bytes used by all xkey_ochead objects Total bytes used by ochead objects. Increases when an object is added to a key or a key is added to an object. Decreases when the relationship is removed. g_oc_bytes gauge - debug Bytes used by all xkey_oc objects Total bytes used by oc objects. Tracks linearly with the number of cached objects that are referenced by surrogate keys. g_bytes gauge - info Bytes used by xkeys Current number of bytes used by xkeys and their references to the object cache. VMOD_XKEY(3)
NAME | SYNOPSIS | DESCRIPTION | XKEY XKEY COUNTERS
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