Mailing List Archive: Effective limits to rules in local.cf

Please forgive me for asking what I'm sure is a common question, but
I've checked every faq, site and archive of this list I can find to no
avail. Is there practical limit to the number of rules I can add to
local.cf?

Thanks in adavance

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At 09:05 AM 2/16/04 -0600, Wood, Thomas wrote:
>Please forgive me for asking what I'm sure is a common question, but
>I've checked every faq, site and archive of this list I can find to no
>avail. Is there practical limit to the number of rules I can add to
>local.cf?

It's really less limited by the number of rules, and usually more limited
by the total complexity of the rules.

Since the rules are in regex syntax, a complicated rule which uses
multi-path string matching with lots of backtracing can take as much time
to execute as dozens of simple rules, if not a hundred of them. This is
going to cause CPU exhaustion.

Of course, if your system is very low on ram, then the total number of
bytes of strings to search is going to be a big limiter. However, most
heavy-load systems generally have plenty of extra ram (since it's cheap)
and generally just hit a "I'm processing mail slower than it's coming in"
limit.

Really, since "too much" is a function of amount of incoming mail, CPU and
ram resources, as well as rule count and complexity you are probably best
off just doing some real world testing and ease rules in while keeping an
eye on memory and CPU load.