Tips on making regex more performant?

[Gary Willoughby]

Below is an example snippet of code to test for performance of 
regex matches. I need to parse a large log and extract data from 
it and i've noticed a huge increase in time of the loop when 
reading and using regex.

	...
	auto alert = regex(r"^Alert ([0-9]+)");

	while ((line = file.readln()) !is null)
	{
		auto m = match(line, alert);

		if (m)
		{
			alerts++;
		}

		counter++;
	}
	...

Using the above example i parse about 700K lines per second (i'm 
reading from an SSD). If i comment out the regex match function, 
i read at 4.5M lines per second. Considering i need to use about 
8 regex matches and extract data, this figure further drops to 
about 100K lines per second.

Is there anything i can do to speed up regex matching in such a 
scenario? Are there any tips you can share to speed things up?

Thanks.