Merge pull request twitter#629 from twitter/logging-improvement

Improve single-server pool efficiency, log event backend with version

ChangeLog

@@ -1,5 +1,5 @@
  2021-??-??  Tyson Andre
-    * twemproxy: version 0.4.2 release (dev)
+    * twemproxy: version 0.5.0 release (dev)
 	  Fix parsing of redis error response for error type with no space,
 	  add tests (tyson, tom dalton)
 	  Update integration tests, add C unit test suite for 'make check' (tyson)
@@ -23,6 +23,12 @@
 	  Upgrade from libyaml 0.1.4 to 0.2.5 (tyson)
 	  Fix compiler warnings about wrong conversion specifiers in format
 	  strings for logging (tyson)
+	  Log the async backend used and any debug options in the
+	  '--help'/'--version' output.
+	  Add support for many more new redis commands and updates to existing
+	  redis commands (tyson)
+	  Optimization: Skip hashing and choosing server index when a pool has
+	  exactly one server (tyson)
 
  2015-22-06  Manju Rajashekhar  <[email protected]>
     * twemproxy: version 0.4.1 release

src/nc.c

@@ -551,7 +551,22 @@ main(int argc, char **argv)
     }
 
     if (show_version) {
-        log_stderr("This is nutcracker-%s" CRLF, NC_VERSION_STRING);
+        log_stderr("This is nutcracker-%s", NC_VERSION_STRING);
+#if NC_HAVE_EPOLL
+        log_stderr("async event backend: epoll");
+#elif NC_HAVE_KQUEUE
+        log_stderr("async event backend: kqueue");
+#elif NC_HAVE_EVENT_PORTS
+        log_stderr("async event backend: event_ports");
+#else
+        log_stderr("async event backend: unknown");
+#endif
+#if HAVE_ASSERT_PANIC || HAVE_ASSERT_LOG
+        log_stderr("debugging assertions are enabled (--enable-debug=yes|full), nutcracker may be less efficient");
+#endif
+        // Log a blank line after the version
+        log_stderr("");
+
         if (show_help) {
             nc_show_usage();
         }

src/nc_server.c

@@ -647,10 +647,16 @@ uint32_t
 server_pool_idx(const struct server_pool *pool, const uint8_t *key, uint32_t keylen)
 {
     uint32_t hash, idx;
+    uint32_t nserver = array_n(&pool->server);
 
-    ASSERT(array_n(&pool->server) != 0);
+    ASSERT(nserver != 0);
     ASSERT(key != NULL);
 
+    if (nserver == 1) {
+        /* Optimization: Skip hashing and dispatching for pools with only one server */
+        return 0;
+    }
+
     /*
      * If hash_tag: is configured for this server pool, we use the part of
      * the key within the hash tag as an input to the distributor. Otherwise