Aide:CirrusSearch/Expression régulière trop complexe

Note : si vous modifiez cette page, vous acceptez de placer votre contribution sous licence CC0. Plus d’informations sont disponibles sur le projet Aide dans le domaine public.

The insource:// syntax implements reasonably efficient regular expression searches written in Lucene's dialect. Pour des raisons de performance, il y a une limite sur la complexité des expressions régulières.

Quelle syntaxe est dite complexe ?

The biggest increases in complexity come from non-determinism followed by repetition. That looks like this:

insource:/[ac]*a[ac]{50,200}/

The [ac]* part is non-deterministic and the [ac]{50,200} is a repeat. On the other hand this is better:

insource:/[ac]*a[de]{50,200}/

Because [de]{50,200} doesn't overlap with [ac]*. It's still complex and still cannot be fully accelerated but it isn't rejected outright and we will try to match it.

Generally the repetition adds more complexity than it is worth. Better to just repeat, so:

insource:/[ac]*a.*[^"]+\"/

is much less complex than:

insource:/[ac]*a.*[^"]{50,100}\"/

Pourquoi ?

Lucene compiles regular expressions to DFAs. It does this by converting the regular expressions to NFAs and then converting those to DFAs. The worst case complexity for that operation is exponential on the number of states in the NFA and the NFA's number of states is related to the regular expression. Non-determinism followed by repetition followed by repetition triggers that exponential state growth. We limit the number of states to 20,000 to prevent them from eating all of our memory.