MDEV-22203: WSREP_ON is unnecessarily expensive WITH_WSREP=OFF

If the server is compiled WITH_WSREP=OFF, we should avoid evaluating
conditions on a global variable that is constant.

WSREP_ON_: Renamed from WSREP_ON. Defined only WITH_WSREP=ON.

WSREP_ON: Defined as unlikely(WSREP_ON_).

wsrep_on(): Defined as WSREP_ON && wsrep_service->wsrep_on_func().

The reason why we have wsrep_on() at all is that the macro WSREP(thd)
depends on the definition of THD, and that is intentionally an opaque
data type for InnoDB. So, we cannot avoid invoking wsrep_on(), but
we can evaluate the less expensive condition WSREP_ON before calling
the function.

include/mysql/service_wsrep.h

@@ -13,7 +13,7 @@ enum Wsrep_service_key_type
 
 #else
 
-/* Copyright (c) 2015 MariaDB Corporation Ab
+/* Copyright (c) 2015, 2020, MariaDB Corporation Ab
                  2018 Codership Oy <info@codership.com>
 
    This program is free software; you can redistribute it and/or modify
@@ -97,7 +97,7 @@ extern struct wsrep_service_st {
 #define wsrep_is_wsrep_xid(X) wsrep_service->wsrep_is_wsrep_xid_func(X)
 #define wsrep_xid_seqno(X) wsrep_service->wsrep_xid_seqno_func(X)
 #define wsrep_xid_uuid(X) wsrep_service->wsrep_xid_uuid_func(X)
-#define wsrep_on(X) wsrep_service->wsrep_on_func(X)
+#define wsrep_on(X) WSREP_ON && wsrep_service->wsrep_on_func(X)
 #define wsrep_prepare_key_for_innodb(A,B,C,D,E,F,G) wsrep_service->wsrep_prepare_key_for_innodb_func(A,B,C,D,E,F,G)
 #define wsrep_thd_LOCK(T) wsrep_service->wsrep_thd_LOCK_func(T)
 #define wsrep_thd_UNLOCK(T) wsrep_service->wsrep_thd_UNLOCK_func(T)

sql/mysqld.cc

@@ -1136,7 +1136,13 @@ PSI_file_key key_file_binlog_state;
 PSI_statement_info stmt_info_new_packet;
 #endif
 
-my_bool WSREP_ON= false;
+#ifdef WITH_WSREP
+/** Whether the Galera write-set replication is enabled. A cached copy of
+global_system_variables.wsrep_on && wsrep_provider &&
+  strcmp(wsrep_provider, WSREP_NONE)
+*/
+bool WSREP_ON_;
+#endif /* WITH_WSREP */
 
 #ifndef EMBEDDED_LIBRARY
 void net_before_header_psi(struct st_net *net, void *thd, size_t /* unused: count */)
@@ -5719,14 +5725,12 @@ int mysqld_main(int argc, char **argv)
   }
 
 #ifdef WITH_WSREP
-  WSREP_ON= (global_system_variables.wsrep_on &&
+  WSREP_ON_= (global_system_variables.wsrep_on &&
           wsrep_provider &&
           strcmp(wsrep_provider, WSREP_NONE));
-#else
-  WSREP_ON= false;
-#endif
 
   if (WSREP_ON && wsrep_check_opts()) unireg_abort(1);
+#endif
 
   /* 
    The subsequent calls may take a long time : e.g. innodb log read.

sql/wsrep_mysqld.cc

@@ -770,10 +770,7 @@ int wsrep_init()
 
   global_system_variables.wsrep_on= 1;
 
-  if (wsrep_provider && strcmp(wsrep_provider, WSREP_NONE))
-    WSREP_ON= true;
-  else
-    WSREP_ON= false;
+  WSREP_ON_= wsrep_provider && strcmp(wsrep_provider, WSREP_NONE);
 
   if (wsrep_gtid_mode && opt_bin_log && !opt_log_slave_updates)
   {

sql/wsrep_mysqld.h

@@ -18,9 +18,8 @@
 
 #include <wsrep.h>
 
-extern my_bool WSREP_ON;
-
 #ifdef WITH_WSREP
+extern bool WSREP_ON_;
 
 #include <mysql/plugin.h>
 #include "mysql/service_wsrep.h"
@@ -215,6 +214,7 @@ extern void wsrep_prepend_PATH (const char* path);
 
 /* Other global variables */
 extern wsrep_seqno_t wsrep_locked_seqno;
+#define WSREP_ON unlikely(WSREP_ON_)
 
 /* use xxxxxx_NNULL macros when thd pointer is guaranteed to be non-null to
  * avoid compiler warnings (GCC 6 and later) */
@@ -480,6 +480,7 @@ enum wsrep::streaming_context::fragment_unit wsrep_fragment_unit(ulong unit);
 /* These macros are needed to compile MariaDB without WSREP support
  * (e.g. embedded) */
 
+#define WSREP_ON false
 #define WSREP(T)  (0)
 #define WSREP_NNULL(T) (0)
 #define WSREP_EMULATE_BINLOG(thd) (0)

sql/wsrep_var.cc

@@ -88,13 +88,10 @@ static bool refresh_provider_options()
   }
 }
 
-static void wsrep_set_wsrep_on(void)
+static void wsrep_set_wsrep_on()
 {
-  if (global_system_variables.wsrep_on && wsrep_provider &&
-      strcmp(wsrep_provider, WSREP_NONE))
-    WSREP_ON= true;
-  else
-    WSREP_ON= false;
+  WSREP_ON_= global_system_variables.wsrep_on && wsrep_provider &&
+    strcmp(wsrep_provider, WSREP_NONE);
 }
 
 /* This is intentionally declared as a weak global symbol, so that

storage/innobase/dict/dict0stats_bg.cc

 /*****************************************************************************
 
 Copyright (c) 2012, 2017, Oracle and/or its affiliates. All Rights Reserved.
-Copyright (c) 2017, 2019, MariaDB Corporation.
+Copyright (c) 2017, 2020, MariaDB Corporation.
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -180,8 +180,8 @@ void dict_stats_update_if_needed_func(dict_table_t* table)
 			lock waits to be enqueued at head of waiting
 			queue. */
 			if (thd
-			    && !wsrep_thd_is_applying(thd)
 			    && wsrep_on(thd)
+			    && !wsrep_thd_is_applying(thd)
 			    && wsrep_thd_is_BF(thd, 0)) {
 				WSREP_DEBUG("Avoiding background statistics"
 					    " calculation for table %s.",

storage/innobase/include/lock0lock.h

 /*****************************************************************************
 
 Copyright (c) 1996, 2016, Oracle and/or its affiliates. All Rights Reserved.
-Copyright (c) 2017, 2019, MariaDB Corporation.
+Copyright (c) 2017, 2020, MariaDB Corporation.
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -1046,7 +1046,7 @@ lock_get_info(
 
 /*******************************************************************//**
 @return whether wsrep_on is true on trx->mysql_thd*/
-#define wsrep_on_trx(trx) ((trx)->mysql_thd && wsrep_on((trx)->mysql_thd))
+#define wsrep_on_trx(trx) wsrep_on((trx)->mysql_thd)
 
 #endif /* WITH_WSREP */