[Varnish] #1375: Varnish performance appears to be impacted by the presence of many vary headers

[Varnish]

#1375: Varnish performance appears to be impacted by the presence of many vary
headers
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 Reporter:  closer01  |       Owner:
     Type:  defect    |      Status:  closed
 Priority:  normal    |   Milestone:
Component:  varnishd  |     Version:  3.0.4
 Severity:  normal    |  Resolution:  worksforme
 Keywords:            |
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Changes (by phk):

 * status:  new => closed
 * resolution:   => worksforme


Comment:

 Sorry about the long delay in answering, for some reason we had all
 overlooked this ticket.

 The scenarios you report on are not typical and varnish is not aimed at
 them.

 However, Varnish will handle them incredibly efficient, but you have to
 force the Vary'ants into the hash-key, rather than rely on the built in
 vary mechanism.

 The sort explanation is that we keep the Vary-ants on a linked list under
 the hash-key, so many vary-ants, either through man vary headers or
 through many variants, causes this link to become longer than good is.

 If instead you add the vary criteria to the hash-key (in vcl_hash{}) you
 get more hash-keys, but each with a shorter linked list, and the
 performance should not suffer at all, quite the contrary:  It will be
 faster than doing Vary processing.

 The downside is that you need to tell your VCL about the structure of your
 objects vary-ances, which is less general.

-- 
Ticket URL: <https://www.varnish-cache.org/trac/ticket/1375#comment:2>
Varnish <https://varnish-cache.org/>
The Varnish HTTP Accelerator