Merge pull request #5191 from yandex/regexp_extraction_fix

Regexp extraction fix for small prefixes

dbms/src/Common/OptimizedRegularExpression.cpp

 #include <Common/Exception.h>
 #include <Common/OptimizedRegularExpression.h>
 
-
 #define MIN_LENGTH_FOR_STRSTR 3
 #define MAX_SUBPATTERNS 5
 
@@ -214,23 +213,38 @@ void OptimizedRegularExpressionImpl<thread_safe>::analyze(
             /** We choose the non-alternative substring of the maximum length, among the prefixes,
               *  or a non-alternative substring of maximum length.
               */
+
+            /// Tuning for typical usage domain
+            auto tuning_strings_condition = [](const std::string & str)
+            {
+                return str != "://" && str != "http://" && str != "www" && str != "Windows ";
+            };
             size_t max_length = 0;
             Substrings::const_iterator candidate_it = trivial_substrings.begin();
             for (Substrings::const_iterator it = trivial_substrings.begin(); it != trivial_substrings.end(); ++it)
             {
                 if (((it->second == 0 && candidate_it->second != 0)
                         || ((it->second == 0) == (candidate_it->second == 0) && it->first.size() > max_length))
-                    /// Tuning for typical usage domain
-                    && (it->first.size() > strlen("://") || strncmp(it->first.data(), "://", strlen("://")))
-                    && (it->first.size() > strlen("http://") || strncmp(it->first.data(), "http", strlen("http")))
-                    && (it->first.size() > strlen("www.") || strncmp(it->first.data(), "www", strlen("www")))
-                    && (it->first.size() > strlen("Windows ") || strncmp(it->first.data(), "Windows ", strlen("Windows "))))
+                    && tuning_strings_condition(it->first))
                 {
                     max_length = it->first.size();
                     candidate_it = it;
                 }
             }
 
+            /// If prefix is small, it won't be chosen
+            if (max_length < MIN_LENGTH_FOR_STRSTR)
+            {
+                for (Substrings::const_iterator it = trivial_substrings.begin(); it != trivial_substrings.end(); ++it)
+                {
+                    if (it->first.size() > max_length && tuning_strings_condition(it->first))
+                    {
+                        max_length = it->first.size();
+                        candidate_it = it;
+                    }
+                }
+            }
+
             if (max_length >= MIN_LENGTH_FOR_STRSTR)
             {
                 required_substring = candidate_it->first;