Ban strategy

[Lyle Mantooth]

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Hello list,

I've noticed that Varnish tends to use more and more CPU as time goes
on, and everything I've read points to a large ban list being
responsible. That sounds reasonable, but I don't think our ban list is
particularly large, even at the busiest of times. On the other hand,
it's hardly ever empty because our content team is constantly making
changes throughout our catalog.

So I come to you, Varnish experts, to see if there's a better way to
construct our ban regexes. Currently, our CMS collects the URLs that a
product might appear on and bans them all at once like so:

```
ban obj.http.x-url ~
^/node/123$|^/product/title$|^/category/77$|^/catalog/title$
ban obj.http.x-url ~
^/node/124$|^/product/other$|^/category/77$|^/catalog/title$
```

It is often the case that several products in a category will be
updated more or less together, so the category pages would be matched
by several bans in the list. Which is easier on the ban lurker:
combined bans like this or more, but simpler, bans that are easier to
match? Even when that would mean more duplicate bans to be issued for
category pages?

- -- 
- --Lyle Mantooth
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