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Docs: Mention the new ban_any_variant param in purging.rst
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walid-git committed Jan 22, 2025
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Expand Up @@ -88,6 +88,23 @@ the regular expression is required by the Varnish cli interface.
Bans are checked when we hit an object in the cache, but before we
deliver it. *An object is only checked against newer bans*.

During lookup, object variants that may not satisfy the current request
are also tested against the ban list, which means that a ban may also
hit a non matching variant.

However, the parameter `ban_any_variant` can be used to limit the number
of possibly non matching variants that are checked against the ban list during
lookup for a particular request. This means that at most `ban_any_variant`
variants will be evaluated, and possibly evicted, before looking for matching
variants. A value of 0 means that every request would only evaluate bans
against matching variants. In contrast, a value that is too high may cause a
request to evaluate all variants against all active bans, which can add
significant delays for configurations having a large number of variants
and/or bans.

In the next major release of varnish (8.0), the default value of
`ban_any_variant` will be set to 0.

Bans that only match against `obj.*` are also processed by a background
worker threads called the `ban lurker`. The `ban lurker` will walk the
heap and try to match objects and will evict the matching objects. How
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