Oh dear, a scaling problem I solved was replacing some Regex matching with simpler string functions. While I'm a huge fan of Regex, it's unreal how much performance they can suck out of some high-n loops...
I got about 120x out of some critical code thus making a CPU upgrade unnecessary.

the key to using regex:

* as much as needed.

* as little as possible.

* and then a bit less.

and document _precisely_ what and how a regex (of any non-trivial complexity) is doing. even near-future-you will thank you.

That must have been either: A really bad regexp, a really bad algorithm leading to multiple use of the regexp on the same data, or just a heeeeeeeeap of data.

Unless this is a log dump processing done using regexs on each of the log lines...

I like this kind of rant because it makes me discover things I didn't know.

@Oktokolo If I remember it correctly it was just the usual JavaScript String.match(...). V8 should be able to optimize this pretty well, but I think there will still be some overhead left.

@Paps Yeah, we'll never stop learning new things, independent of seniority.

Wow, some regexp hater seems to do multi-account downvoting here. I seem to get enough upvotes to keep my answer at zero though...

This reminds me of the time I tried to validate IPv4 CIDR ranges with regex. The pattern ended up becoming stupidly complicated until I decided to forego regex entirely. I ended up splitting the string and parsing the octets into numbers, then validated with simple math.

Regex has its place but sometimes it just isn't the best option.

Some things are not suited for regex. It's often used as a hammer while it can be a scalpel.
Also the implementations vary. When you do a loop like that at least use an implementation that can compile the regex and use that.