The Elpi lexer has pathological backtracking that can be triggered with the following minimal input:

from pygments.lexers.elpi import ElpiLexer

list(ElpiLexer().get_tokens("a" * 30))

Only lowercase characters trigger pathological backtracking. Uppercase characters and digits will not.

The culprit is at line 62.

@gares I'm not familiar with Elpi, so if you can jump in to address this, great! Otherwise I'll be able to take a crack at it after this weekend.