Squid configuration directive collapsed_forwarding
Available in: v7 v6 v5 v4 3.5 2.7 2.6
For older versions than v4 see the linked pages above
Configuration Details:
Option Name: | collapsed_forwarding |
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Replaces: | |
Requires: | |
Default Value: | collapsed_forwarding off |
Suggested Config: |
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This option controls whether Squid is allowed to merge multiple potentially cachable requests for the same URI before Squid knows whether the response is going to be cachable. When enabled, instead of forwarding each concurrent request for the same URL, Squid just sends the first of them. The other, so called "collapsed" requests, wait for the response to the first request and, if it happens to be cachable, use that response. Here, "concurrent requests" means "received after the first request headers were parsed and before the corresponding response headers were parsed". This feature is disabled by default: enabling collapsed forwarding needlessly delays forwarding requests that look cachable (when they are collapsed) but then need to be forwarded individually anyway because they end up being for uncachable content. However, in some cases, such as acceleration of highly cachable content with periodic or grouped expiration times, the gains from collapsing [large volumes of simultaneous refresh requests] outweigh losses from such delays. Squid collapses two kinds of requests: regular client requests received on one of the listening ports and internal "cache revalidation" requests which are triggered by those regular requests hitting a stale cached object. Revalidation collapsing is currently disabled for Squid instances containing SMP-aware disk or memory caches and for Vary-controlled cached objects. |
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