> where res_url like '%mts.ru%' ... > where res_url like '%mts_ru%' ... > Why '_' wildcard decrease perfomance?
Because it misses the fast path by just one "_". ORC vectorized reader has a zero-copy check for 3 patterns - prefix, suffix and middle. That means "https://%";, "%.html", "%mts.ru%" will hit the fast path - which uses StringExpr::equal() which JITs into the following. https://issues.apache.org/jira/secure/attachment/12748720/string-intrinsic- sse.png In Hive-2.0, you can mix these up too to get "https:%mts%.html" in a ChainedChecker. Anything other than these 3 cases becomes a Regex and takes the slow path. The pattern you mentioned gets rewritten into ".*mts.ru.*" and the inner loop has a new String() as the input to the matcher + matcher.matches() in it. I've put in some patches recently which rewrite it Lazy regexes like ".?*mts.ru.?*", so the regex DFA will be smaller (HIVE-13196). That improves the case where the pattern is found, but does nothing to improve the performance of the new String() GC garbage. Cheers, Gopal
