Why not use more modern regex tools?

[DL6ER]

@nightynight

What is the cache strategy ?

Evaluate regexes and cache the result per client and domain.

@nightynight

Is there a timeout?

No, there is no need for a timeout as any chance possibly resulting in a change flushes the cache.

@nightynight

What triggers the cache flush ?

Adding/removing domains from the lists, a gravity update or changing groups associated with either clients or domains - everything that could cause a domain's blocking status to change. Pi-hole implements selective flushing per client so small changes do not reset everything.

@nightynight

When I looked it up online I saw lots of posts saying pihole and regex should not be used since it will slow down the query

See @jfb's answer.

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edit To expand on this very incomplete statement:

@nightynight

regex should not be used since it will slow down the query.

is more about Pi-hole being so extremely fast with exact lookups as it is using a B-tree algorithm for its lookups. This all has been explain very often on this forum, see e.g., here for details about the particular why:

Questions on RegEx efficiency

The answer for your first three questions is: No. The reason is that regex are compiled to efficient byte-code before being used. The result of the compilation is used when performing the actual matching. is the shortest way, however, m(ms|mg-fna|edia) may be faster as it is simpler. Checking one simple regex is more work than checking against millions of exact domains. Giving exact numbers is neither straightforward nor easy and will heavily depend on the particular regex we are talking ab…

very short: one million regex will take several seconds to evaluate, one million domains will take less than a millisecond to evaluate. Having two million domains and 500 regex is probably fine, the other way around surely is not. This general statement wouldn't change too much even when the regex engine would be three times faster.