MAJOR: pattern: add LRU-based cache on pattern matching
The principle of this cache is to have a global cache for all pattern
matching operations which rely on lists (reg, sub, dir, dom, ...). The
input data, the expression and a random seed are used as a hashing key.
The cached entries contains a pointer to the expression and a revision
number for that expression so that we don't accidently used obsolete
data after a pattern update or a very unlikely hash collision.
Regarding the risk of collisions, 10k entries at 10k req/s mean 1% risk
of a collision after 60 years, that's already much less than the memory's
reliability in most machines and more durable than most admin's life
expectancy. A collision will result in a valid result to be returned
for a different entry from the same list. If this is not acceptable,
the cache can be disabled using tune.pattern.cache-size.
A test on a file containing 10k small regex showed that the regex
matching was limited to 6k/s instead of 70k with regular strings.
When enabling the LRU cache, the performance was back to 70k/s.
diff --git a/include/common/defaults.h b/include/common/defaults.h
index 63b2b89..6193bdc 100644
--- a/include/common/defaults.h
+++ b/include/common/defaults.h
@@ -295,4 +295,15 @@
#ifndef TLS_TICKETS_NO
#define TLS_TICKETS_NO 3
#endif
+
+/* pattern lookup default cache size, in number of entries :
+ * 10k entries at 10k req/s mean 1% risk of a collision after 60 years, that's
+ * already much less than the memory's reliability in most machines and more
+ * durable than most admin's life expectancy. A collision will result in a
+ * valid result to be returned for a different entry from the same list.
+ */
+#ifndef DEFAULT_PAT_LRU_SIZE
+#define DEFAULT_PAT_LRU_SIZE 10000
+#endif
+
#endif /* _COMMON_DEFAULTS_H */