diff --git a/CMakeLists.txt b/CMakeLists.txt
index 036d0cdb9d6..d20939f33ac 100755
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -32,26 +32,32 @@ IF(DEFINED CMAKE_BUILD_TYPE)
   SET(HAVE_CMAKE_BUILD_TYPE TRUE)
 ENDIF()
 SET(CUSTOM_C_FLAGS $ENV{CFLAGS})
-IF(NOT CUSTOM_C_FLAGS)
-  SET(CUSTOM_C_FLAGS ${CMAKE_C_FLAGS})
-ENDIF()
 
-OPTION(WITH_DEBUG "Use dbug" OFF)
+OPTION(WITH_DEBUG "Use dbug/safemutex" OFF)
 OPTION(WITH_DEBUG_FULL "Use dbug and safemalloc/safemutex. Slow" OFF)
 
-IF(NOT HAVE_CMAKE_BUILD_TYPE)
-   IF(BUILD_CONFIG OR NOT CUSTOM_C_FLAGS)
-     IF(WITH_DEBUG)
-       SET(CMAKE_BUILD_TYPE "Debug" CACHE STRING "Debug build" FORCE)
-     ELSE()
-       SET(CMAKE_BUILD_TYPE "RelWithDebInfo" CACHE STRING 
-        "RelWithDebInfo build" FORCE)
-     ENDIF()
-   ENDIF()
-ENDIF()
 
-IF(WITH_DEBUG_FULL)
-  SET(WITH_DEBUG ON CACHE BOOL "Use DBUG")
+# We choose to provide WITH_DEBUG as alias to standard CMAKE_BUILD_TYPE=Debug
+# which turns out to be not trivial, as this involves synchronization 
+# between CMAKE_BUILD_TYPE and WITH_DEBUG. Besides, we have to deal with cases
+# where WITH_DEBUG is  reset from ON to OFF  and here we need to reset 
+# CMAKE_BUILD_TYPE to either none or default RelWithDebInfo
+
+SET(BUILDTYPE_DOCSTRING
+ "Choose the type of build, options are: None(CMAKE_CXX_FLAGS or
+ CMAKE_C_FLAGS used) Debug Release RelWithDebInfo MinSizeRel")
+ 
+IF(WITH_DEBUG OR WITH_DEBUG_FULL)
+  SET(CMAKE_BUILD_TYPE "Debug" CACHE STRING ${BUILDTYPE_DOCSTRING} FORCE)
+  SET(OLD_WITH_DEBUG 1 CACHE INTERNAL "" FORCE)
+ELSEIF(NOT HAVE_CMAKE_BUILD_TYPE OR OLD_WITH_DEBUG)
+  IF(CUSTOM_C_FLAGS)
+    SET(CMAKE_BUILD_TYPE "" CACHE STRING ${BUILDTYPE_DOCSTRING} FORCE)
+  ELSE(CMAKE_BUILD_TYPE MATCHES "Debug" OR NOT HAVE_CMAKE_BUILD_TYPE)
+    SET(CMAKE_BUILD_TYPE "RelWithDebInfo" CACHE STRING 
+       ${BUILDTYPE_DOCSTRING} FORCE)
+  ENDIF()
+  SET(OLD_WITH_DEBUG 0 CACHE INTERNAL "" FORCE)
 ENDIF()
 
 IF(BUILD_CONFIG)
diff --git a/config.h.cmake b/config.h.cmake
index eb1a5e24ec8..f0473c83af6 100644
--- a/config.h.cmake
+++ b/config.h.cmake
@@ -205,6 +205,7 @@
 #cmakedefine HAVE_PTHREAD_KEY_DELETE 1
 #cmakedefine HAVE_PTHREAD_KILL 1
 #cmakedefine HAVE_PTHREAD_RWLOCK_RDLOCK 1
+#cmakedefine HAVE_PTHREAD_RWLOCKATTR_SETKIND_NP 1
 #cmakedefine HAVE_PTHREAD_SETPRIO_NP 1
 #cmakedefine HAVE_PTHREAD_SETSCHEDPARAM 1
 #cmakedefine HAVE_PTHREAD_SIGMASK 1
diff --git a/configure.cmake b/configure.cmake
index 243d3b03b45..31e38aaa2cd 100644
--- a/configure.cmake
+++ b/configure.cmake
@@ -308,6 +308,7 @@ CHECK_FUNCTION_EXISTS (pthread_condattr_setclock HAVE_PTHREAD_CONDATTR_SETCLOCK)
 CHECK_FUNCTION_EXISTS (pthread_init HAVE_PTHREAD_INIT)
 CHECK_FUNCTION_EXISTS (pthread_key_delete HAVE_PTHREAD_KEY_DELETE)
 CHECK_FUNCTION_EXISTS (pthread_rwlock_rdlock HAVE_PTHREAD_RWLOCK_RDLOCK)
+CHECK_FUNCTION_EXISTS (pthread_rwlockattr_setkind_np HAVE_PTHREAD_RWLOCKATTR_SETKIND_NP)
 CHECK_FUNCTION_EXISTS (pthread_sigmask HAVE_PTHREAD_SIGMASK)
 CHECK_FUNCTION_EXISTS (pthread_threadmask HAVE_PTHREAD_THREADMASK)
 CHECK_FUNCTION_EXISTS (pthread_yield_np HAVE_PTHREAD_YIELD_NP)
diff --git a/configure.in b/configure.in
index 3280c979c8c..c2a8ce86e08 100644
--- a/configure.in
+++ b/configure.in
@@ -2266,7 +2266,8 @@ AC_CHECK_FUNCS(alarm bcmp bfill bmove bsearch bzero \
   locking longjmp lrand48 madvise mallinfo memcpy memmove \
   mkstemp mlockall perror poll pread pthread_attr_create mmap mmap64 getpagesize \
   pthread_attr_getstacksize pthread_attr_setstacksize pthread_condattr_create \
-  pthread_getsequence_np pthread_key_delete pthread_rwlock_rdlock pthread_sigmask \
+  pthread_getsequence_np pthread_key_delete pthread_rwlock_rdlock \
+  pthread_rwlockattr_setkind_np pthread_sigmask \
   readlink realpath rename rint rwlock_init setupterm \
   shmget shmat shmdt shmctl sigaction sigemptyset sigaddset \
   sighold sigset sigthreadmask port_create sleep thr_yield \
diff --git a/include/my_pthread.h b/include/my_pthread.h
index 0e421f678b0..0b55c70b0fa 100644
--- a/include/my_pthread.h
+++ b/include/my_pthread.h
@@ -600,30 +600,76 @@ int my_pthread_fastmutex_lock(my_pthread_fastmutex_t *mp);
 #define my_rwlock_init(A,B) rwlock_init((A),USYNC_THREAD,0)
 #else
 /* Use our own version of read/write locks */
-typedef struct _my_rw_lock_t {
-	pthread_mutex_t lock;		/* lock for structure		*/
-	pthread_cond_t	readers;	/* waiting readers		*/
-	pthread_cond_t	writers;	/* waiting writers		*/
-	int		state;		/* -1:writer,0:free,>0:readers	*/
-	int		waiters;	/* number of waiting writers	*/
-} my_rw_lock_t;
-
+#define NEED_MY_RW_LOCK 1
 #define rw_lock_t my_rw_lock_t
+#define my_rwlock_init(A,B) my_rw_init((A), 0)
 #define rw_rdlock(A) my_rw_rdlock((A))
 #define rw_wrlock(A) my_rw_wrlock((A))
 #define rw_tryrdlock(A) my_rw_tryrdlock((A))
 #define rw_trywrlock(A) my_rw_trywrlock((A))
 #define rw_unlock(A) my_rw_unlock((A))
-#define rwlock_destroy(A) my_rwlock_destroy((A))
+#define rwlock_destroy(A) my_rw_destroy((A))
+#endif /* USE_MUTEX_INSTEAD_OF_RW_LOCKS */
 
-extern int my_rwlock_init(my_rw_lock_t *, void *);
-extern int my_rwlock_destroy(my_rw_lock_t *);
+
+/*
+  Portable read-write locks which prefer readers.
+
+  Required by some algorithms in order to provide correctness.
+*/
+
+#if defined(HAVE_PTHREAD_RWLOCK_RDLOCK) && defined(HAVE_PTHREAD_RWLOCKATTR_SETKIND_NP)
+/*
+  On systems which have a way to specify that readers should
+  be preferred through attribute mechanism (e.g. Linux) we use
+  system implementation of read/write locks.
+*/
+#define rw_pr_lock_t pthread_rwlock_t
+extern int rw_pr_init(rw_pr_lock_t *);
+#define rw_pr_rdlock(A) pthread_rwlock_rdlock(A)
+#define rw_pr_wrlock(A) pthread_rwlock_wrlock(A)
+#define rw_pr_tryrdlock(A) pthread_rwlock_tryrdlock(A)
+#define rw_pr_trywrlock(A) pthread_rwlock_trywrlock(A)
+#define rw_pr_unlock(A) pthread_rwlock_unlock(A)
+#define rw_pr_destroy(A) pthread_rwlock_destroy(A)
+#else
+/* Otherwise we have to use our own implementation of read/write locks. */
+#define NEED_MY_RW_LOCK 1
+struct st_my_rw_lock_t;
+#define rw_pr_lock_t my_rw_lock_t
+extern int rw_pr_init(struct st_my_rw_lock_t *);
+#define rw_pr_rdlock(A) my_rw_rdlock((A))
+#define rw_pr_wrlock(A) my_rw_wrlock((A))
+#define rw_pr_tryrdlock(A) my_rw_tryrdlock((A))
+#define rw_pr_trywrlock(A) my_rw_trywrlock((A))
+#define rw_pr_unlock(A) my_rw_unlock((A))
+#define rw_pr_destroy(A) my_rw_destroy((A))
+#endif /* defined(HAVE_PTHREAD_RWLOCK_RDLOCK) && defined(HAVE_PTHREAD_RWLOCKATTR_SETKIND_NP) */
+
+
+#ifdef NEED_MY_RW_LOCK
+/*
+  On systems which don't support native read/write locks, or don't support
+  read/write locks which prefer readers we have to use own implementation.
+*/
+typedef struct st_my_rw_lock_t {
+	pthread_mutex_t lock;		/* lock for structure		*/
+	pthread_cond_t	readers;	/* waiting readers		*/
+	pthread_cond_t	writers;	/* waiting writers		*/
+	int		state;		/* -1:writer,0:free,>0:readers	*/
+	int             waiters;        /* number of waiting writers	*/
+	my_bool         prefer_readers;
+} my_rw_lock_t;
+
+extern int my_rw_init(my_rw_lock_t *, my_bool *);
+extern int my_rw_destroy(my_rw_lock_t *);
 extern int my_rw_rdlock(my_rw_lock_t *);
 extern int my_rw_wrlock(my_rw_lock_t *);
 extern int my_rw_unlock(my_rw_lock_t *);
 extern int my_rw_tryrdlock(my_rw_lock_t *);
 extern int my_rw_trywrlock(my_rw_lock_t *);
-#endif /* USE_MUTEX_INSTEAD_OF_RW_LOCKS */
+#endif /* NEED_MY_RW_LOCK */
+
 
 #define GETHOSTBYADDR_BUFF_SIZE 2048
 
diff --git a/mysql-test/r/flush.result b/mysql-test/r/flush.result
index 2136bcd92f1..fd23bfa0562 100644
--- a/mysql-test/r/flush.result
+++ b/mysql-test/r/flush.result
@@ -111,3 +111,99 @@ commit;
 # which was already released by commit.
 unlock tables;
 drop tables t1, t2;
+# 
+# Tests for WL#5000  FLUSH TABLES|TABLE table_list WITH READ LOCK
+#
+# I. Check the incompatible changes in the grammar.
+#
+flush tables with read lock, hosts;
+ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ' hosts' at line 1
+flush privileges, tables;
+ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'tables' at line 1
+flush privileges, tables with read lock;
+ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'tables with read lock' at line 1
+flush privileges, tables;
+ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'tables' at line 1
+flush tables with read lock, tables;
+ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ' tables' at line 1
+show tables;
+Tables_in_test
+#
+# II. Check the allowed syntax.
+#
+drop table if exists t1, t2, t3;
+create table t1 (a int);
+create table t2 (a int);
+create table t3 (a int);
+lock table t1 read, t2 read;
+flush tables with read lock;
+ERROR HY000: Can't execute the given command because you have active locked tables or an active transaction
+unlock tables;
+flush tables with read lock;
+flush tables t1, t2 with read lock;
+flush tables t1, t2 with read lock;
+ERROR HY000: Can't execute the given command because you have active locked tables or an active transaction
+flush tables with read lock;
+ERROR HY000: Can't execute the given command because you have active locked tables or an active transaction
+select * from t1;
+a
+select * from t2;
+a
+select * from t3;
+ERROR HY000: Table 't3' was not locked with LOCK TABLES
+insert into t1 (a) values (1);
+ERROR HY000: Table 't1' was locked with a READ lock and can't be updated
+insert into t2 (a) values (1);
+ERROR HY000: Table 't2' was locked with a READ lock and can't be updated
+insert into t3 (a) values (1);
+ERROR HY000: Table 't3' was not locked with LOCK TABLES
+lock table no_such_table read;
+ERROR 42S02: Table 'test.no_such_table' doesn't exist
+#
+# We implicitly left the locked tables
+# mode but still have the read lock.
+# 
+insert into t2 (a) values (1);
+ERROR HY000: Can't execute the query because you have a conflicting read lock
+unlock tables;
+insert into t1 (a) values (1);
+insert into t2 (a) values (1);
+flush table t1, t2 with read lock;
+select * from t1;
+a
+1
+select * from t2;
+a
+1
+select * from t3;
+ERROR HY000: Table 't3' was not locked with LOCK TABLES
+insert into t1 (a) values (2);
+ERROR HY000: Table 't1' was locked with a READ lock and can't be updated
+insert into t2 (a) values (2);
+ERROR HY000: Table 't2' was locked with a READ lock and can't be updated
+insert into t3 (a) values (2);
+ERROR HY000: Table 't3' was not locked with LOCK TABLES
+lock table no_such_table read;
+ERROR 42S02: Table 'test.no_such_table' doesn't exist
+insert into t3 (a) values (2);
+# 
+# III. Concurrent tests.
+#
+# --> connection default
+#
+# Check that flush tables <list> with read lock
+# does not affect non-locked tables.
+#
+flush tables t1 with read lock;
+# --> connection con1;
+select * from t1;
+a
+1
+select * from t2;
+a
+1
+insert into t2 (a) values (3);
+# --> connection default;
+unlock tables;
+# --> connection con1
+drop table t1, t2, t3;
diff --git a/mysql-test/r/greedy_optimizer.result b/mysql-test/r/greedy_optimizer.result
index c0012c297d1..be4b06396a8 100644
--- a/mysql-test/r/greedy_optimizer.result
+++ b/mysql-test/r/greedy_optimizer.result
@@ -115,6 +115,8 @@ select @@optimizer_prune_level;
 @@optimizer_prune_level
 1
 set optimizer_search_depth=63;
+Warnings:
+Warning	1287	'optimizer-search-depth=63' is deprecated and will be removed in a future release. Please use a search depth less than 63 instead
 select @@optimizer_search_depth;
 @@optimizer_search_depth
 63
diff --git a/mysql-test/r/mysqld--help-notwin.result b/mysql-test/r/mysqld--help-notwin.result
index 5c4a13a3c7e..711402c764f 100644
--- a/mysql-test/r/mysqld--help-notwin.result
+++ b/mysql-test/r/mysqld--help-notwin.result
@@ -396,8 +396,9 @@ The following options may be given as the first argument:
  relation result in faster optimization, but may produce
  very bad query plans. If set to 0, the system will
  automatically pick a reasonable value; if set to 63, the
- optimizer will switch to the original find_best
- search(used for testing/comparison)
+ optimizer will switch to the original find_best search.
+ NOTE: The value 63 and its associated behaviour is
+ deprecated
  --optimizer-switch=name 
  optimizer_switch=option=val[,option=val...], where option
  is one of {index_merge, index_merge_union,
diff --git a/mysql-test/r/mysqld--help-win.result b/mysql-test/r/mysqld--help-win.result
index 15649cbc0fa..9804cfce78b 100644
--- a/mysql-test/r/mysqld--help-win.result
+++ b/mysql-test/r/mysqld--help-win.result
@@ -396,8 +396,9 @@ The following options may be given as the first argument:
  relation result in faster optimization, but may produce
  very bad query plans. If set to 0, the system will
  automatically pick a reasonable value; if set to 63, the
- optimizer will switch to the original find_best
- search(used for testing/comparison)
+ optimizer will switch to the original find_best search.
+ NOTE: The value 63 and its associated behaviour is
+ deprecated
  --optimizer-switch=name 
  optimizer_switch=option=val[,option=val...], where option
  is one of {index_merge, index_merge_union,
diff --git a/mysql-test/suite/large_tests/r/rpl_slave_net_timeout.result b/mysql-test/suite/large_tests/r/rpl_slave_net_timeout.result
new file mode 100644
index 00000000000..81de6e228e0
--- /dev/null
+++ b/mysql-test/suite/large_tests/r/rpl_slave_net_timeout.result
@@ -0,0 +1,25 @@
+stop slave;
+drop table if exists t1,t2,t3,t4,t5,t6,t7,t8,t9;
+reset master;
+reset slave;
+drop table if exists t1,t2,t3,t4,t5,t6,t7,t8,t9;
+start slave;
+set @save_general_log = @@global.general_log;
+set @save_log_output = @@global.log_output;
+set @save_slave_net_timeout = @@global.slave_net_timeout;
+set @@global.general_log = ON;
+set @@global.log_output = 'table,file';
+include/stop_slave.inc
+set @@global.slave_net_timeout = @@global.net_read_timeout * 2;
+change master to master_host = '127.0.0.1',master_port = MASTER_PORT,
+master_user = 'root', master_heartbeat_period = 0;
+include/start_slave.inc
+include/stop_slave.inc
+select event_time from (select event_time from mysql.general_log as t_1 where command_type like 'Connect' order by event_time desc limit 2) as t_2 order by event_time desc limit 1 into @ts_last;
+select event_time from (select event_time from mysql.general_log as t_1 where command_type like 'Connect' order by event_time desc limit 2) as t_2 order by event_time asc limit 1 into @ts_prev;
+select @result as 'Must be 1';
+Must be 1
+1
+set @@global.general_log = @save_general_log;
+set @@global.log_output = @save_log_output;
+set @@global.slave_net_timeout = @save_slave_net_timeout;
diff --git a/mysql-test/suite/large_tests/t/rpl_slave_net_timeout-slave.opt b/mysql-test/suite/large_tests/t/rpl_slave_net_timeout-slave.opt
new file mode 100644
index 00000000000..281566c9ad9
--- /dev/null
+++ b/mysql-test/suite/large_tests/t/rpl_slave_net_timeout-slave.opt
@@ -0,0 +1 @@
+--net_read_timeout=5
diff --git a/mysql-test/suite/large_tests/t/rpl_slave_net_timeout.test b/mysql-test/suite/large_tests/t/rpl_slave_net_timeout.test
new file mode 100644
index 00000000000..9a2cdc3b596
--- /dev/null
+++ b/mysql-test/suite/large_tests/t/rpl_slave_net_timeout.test
@@ -0,0 +1,81 @@
+#
+#  Testing reconnecting by slave as specified by `slave_net_timeout'
+#
+#  Bug #50296 Slave reconnects earlier than the prescribed slave_net_timeout value
+#
+--source include/have_csv.inc
+--source include/master-slave.inc
+
+
+# save global env
+connection master;
+set @save_general_log = @@global.general_log;
+set @save_log_output = @@global.log_output;
+
+connection slave;
+set @save_slave_net_timeout = @@global.slave_net_timeout;
+
+connection master;
+set @@global.general_log = ON;
+set @@global.log_output = 'table,file';
+
+connection slave;
+--source include/stop_slave.inc
+--disable_warnings
+set @@global.slave_net_timeout = @@global.net_read_timeout * 2;
+--enable_warnings
+let $idle_time=`select @@global.slave_net_timeout * 2`;
+
+#
+# if heartbeat is disabled then reconnecting to the idle master
+# should happen with `slave_net_timeout' period.
+# Since it's the real time that is measured, `slave_net_timeout'
+# merely guarantees that reconnecting can *not* happen earlier of a value specified.
+# That is there can't an exact estimate for how many time it will happen.
+#
+# The following lines verify that having idle master 
+# for more than 2 * slave_net_timeout seconds and 
+# slave.net_read_timeout < slave_net_timeout
+# won't cause reconnecting by the slave within at least 
+# slave_net_timeout interval.
+--replace_result $MASTER_MYPORT MASTER_PORT 
+eval change master to master_host = '127.0.0.1',master_port = $MASTER_MYPORT,
+master_user = 'root', master_heartbeat_period = 0;
+
+let $slave_net_timeout = `select @@global.slave_net_timeout`;
+
+--source include/start_slave.inc
+
+--disable_query_log
+--disable_result_log
+eval select 'master is idle for ', sleep($idle_time);
+--enable_result_log
+--enable_query_log
+
+--source include/stop_slave.inc
+
+# querying general-log
+
+connection master;
+
+# In particular the last reconnection timestamp must be greater or equal to
+# the previous one + slave_net_timeout
+
+select event_time from (select event_time from mysql.general_log as t_1 where command_type like 'Connect' order by event_time desc limit 2) as t_2 order by event_time desc limit 1 into @ts_last;
+select event_time from (select event_time from mysql.general_log as t_1 where command_type like 'Connect' order by event_time desc limit 2) as t_2 order by event_time asc limit 1 into @ts_prev;
+
+--disable_query_log
+eval select time_to_sec(@ts_last) - $slave_net_timeout >= time_to_sec(@ts_prev) into @result;
+--enable_query_log
+
+select @result as 'Must be 1';
+
+# cleanup 
+
+# restore global env
+connection master;
+set @@global.general_log = @save_general_log;
+set @@global.log_output = @save_log_output;
+connection slave;
+set @@global.slave_net_timeout = @save_slave_net_timeout;
+
diff --git a/mysql-test/suite/perfschema/r/misc.result b/mysql-test/suite/perfschema/r/misc.result
index d944b4b1d3d..3c0a4a58e08 100644
--- a/mysql-test/suite/perfschema/r/misc.result
+++ b/mysql-test/suite/perfschema/r/misc.result
@@ -11,3 +11,17 @@ create table test.t1 like performance_schema.EVENTS_WAITS_CURRENT;
 ERROR HY000: Invalid performance_schema usage.
 create table performance_schema.t1(a int);
 ERROR 42000: CREATE command denied to user 'root'@'localhost' for table 't1'
+drop table if exists test.ghost;
+create table test.ghost (a int, b int);
+alter table test.ghost add index index_a(a);
+alter table test.ghost add index index_b(b);
+insert into test.ghost values (1, 3);
+insert into test.ghost values (2, 4);
+select * from test.ghost;
+a	b
+1	3
+2	4
+drop table test.ghost;
+select * from performance_schema.FILE_INSTANCES
+where file_name like "%ghost%";
+FILE_NAME	EVENT_NAME	OPEN_COUNT
diff --git a/mysql-test/suite/perfschema/t/misc.test b/mysql-test/suite/perfschema/t/misc.test
index d9b97d8441e..749eccca793 100644
--- a/mysql-test/suite/perfschema/t/misc.test
+++ b/mysql-test/suite/perfschema/t/misc.test
@@ -55,3 +55,24 @@ create table test.t1 like performance_schema.EVENTS_WAITS_CURRENT;
 --error ER_TABLEACCESS_DENIED_ERROR
 create table performance_schema.t1(a int);
 
+#
+# Bug#51447 performance schema evil twin files
+#
+
+--disable_warnings
+drop table if exists test.ghost;
+--enable_warnings
+
+create table test.ghost (a int, b int);
+alter table test.ghost add index index_a(a);
+alter table test.ghost add index index_b(b);
+insert into test.ghost values (1, 3);
+insert into test.ghost values (2, 4);
+select * from test.ghost;
+
+drop table test.ghost;
+
+# Shoud return nothing
+select * from performance_schema.FILE_INSTANCES
+  where file_name like "%ghost%";
+
diff --git a/mysql-test/suite/sys_vars/r/optimizer_search_depth_basic.result b/mysql-test/suite/sys_vars/r/optimizer_search_depth_basic.result
index 4d94fb02be7..de448d3e2fc 100644
--- a/mysql-test/suite/sys_vars/r/optimizer_search_depth_basic.result
+++ b/mysql-test/suite/sys_vars/r/optimizer_search_depth_basic.result
@@ -10,6 +10,7 @@ SELECT @start_session_value;
 SET @@global.optimizer_search_depth = 100;
 Warnings:
 Warning	1292	Truncated incorrect optimizer_search_depth value: '100'
+Warning	1287	'optimizer-search-depth=63' is deprecated and will be removed in a future release. Please use a search depth less than 63 instead
 SET @@global.optimizer_search_depth = DEFAULT;
 SELECT @@global.optimizer_search_depth;
 @@global.optimizer_search_depth
@@ -17,6 +18,7 @@ SELECT @@global.optimizer_search_depth;
 SET @@session.optimizer_search_depth = 200;
 Warnings:
 Warning	1292	Truncated incorrect optimizer_search_depth value: '200'
+Warning	1287	'optimizer-search-depth=63' is deprecated and will be removed in a future release. Please use a search depth less than 63 instead
 SET @@session.optimizer_search_depth = DEFAULT;
 SELECT @@session.optimizer_search_depth;
 @@session.optimizer_search_depth
@@ -44,6 +46,8 @@ SELECT @@global.optimizer_search_depth;
 @@global.optimizer_search_depth
 62
 SET @@global.optimizer_search_depth = 63;
+Warnings:
+Warning	1287	'optimizer-search-depth=63' is deprecated and will be removed in a future release. Please use a search depth less than 63 instead
 SELECT @@global.optimizer_search_depth;
 @@global.optimizer_search_depth
 63
@@ -61,6 +65,8 @@ SELECT @@session.optimizer_search_depth;
 @@session.optimizer_search_depth
 62
 SET @@session.optimizer_search_depth = 63;
+Warnings:
+Warning	1287	'optimizer-search-depth=63' is deprecated and will be removed in a future release. Please use a search depth less than 63 instead
 SELECT @@session.optimizer_search_depth;
 @@session.optimizer_search_depth
 63
@@ -68,6 +74,7 @@ SELECT @@session.optimizer_search_depth;
 SET @@global.optimizer_search_depth = 64;
 Warnings:
 Warning	1292	Truncated incorrect optimizer_search_depth value: '64'
+Warning	1287	'optimizer-search-depth=63' is deprecated and will be removed in a future release. Please use a search depth less than 63 instead
 SELECT @@global.optimizer_search_depth;
 @@global.optimizer_search_depth
 63
@@ -80,6 +87,7 @@ SELECT @@global.optimizer_search_depth;
 SET @@global.optimizer_search_depth = 65536;
 Warnings:
 Warning	1292	Truncated incorrect optimizer_search_depth value: '65536'
+Warning	1287	'optimizer-search-depth=63' is deprecated and will be removed in a future release. Please use a search depth less than 63 instead
 SELECT @@global.optimizer_search_depth;
 @@global.optimizer_search_depth
 63
@@ -96,6 +104,7 @@ SELECT @@global.optimizer_search_depth;
 SET @@session.optimizer_search_depth = 64;
 Warnings:
 Warning	1292	Truncated incorrect optimizer_search_depth value: '64'
+Warning	1287	'optimizer-search-depth=63' is deprecated and will be removed in a future release. Please use a search depth less than 63 instead
 SELECT @@session.optimizer_search_depth;
 @@session.optimizer_search_depth
 63
@@ -110,6 +119,7 @@ ERROR 42000: Incorrect argument type to variable 'optimizer_search_depth'
 SET @@session.optimizer_search_depth = 65550;
 Warnings:
 Warning	1292	Truncated incorrect optimizer_search_depth value: '65550'
+Warning	1287	'optimizer-search-depth=63' is deprecated and will be removed in a future release. Please use a search depth less than 63 instead
 SELECT @@session.optimizer_search_depth;
 @@session.optimizer_search_depth
 63
diff --git a/mysql-test/t/flush.test b/mysql-test/t/flush.test
index d41ac3100b0..582d2562fc6 100644
--- a/mysql-test/t/flush.test
+++ b/mysql-test/t/flush.test
@@ -224,3 +224,103 @@ commit;
 --echo # which was already released by commit.
 unlock tables;
 drop tables t1, t2;
+
+
+
+--echo # 
+--echo # Tests for WL#5000  FLUSH TABLES|TABLE table_list WITH READ LOCK
+--echo #
+--echo # I. Check the incompatible changes in the grammar.
+--echo #
+--error ER_PARSE_ERROR
+flush tables with read lock, hosts;
+--error ER_PARSE_ERROR
+flush privileges, tables;
+--error ER_PARSE_ERROR
+flush privileges, tables with read lock;
+--error ER_PARSE_ERROR
+flush privileges, tables;
+--error ER_PARSE_ERROR
+flush tables with read lock, tables;
+show tables;
+--echo #
+--echo # II. Check the allowed syntax.
+--echo #
+--disable_warnings
+drop table if exists t1, t2, t3;
+--enable_warnings
+create table t1 (a int);
+create table t2 (a int);
+create table t3 (a int);
+lock table t1 read, t2 read;
+--error ER_LOCK_OR_ACTIVE_TRANSACTION
+flush tables with read lock;
+unlock tables;
+flush tables with read lock;
+flush tables t1, t2 with read lock;
+--error ER_LOCK_OR_ACTIVE_TRANSACTION
+flush tables t1, t2 with read lock;
+--error ER_LOCK_OR_ACTIVE_TRANSACTION
+flush tables with read lock;
+select * from t1;
+select * from t2;
+--error ER_TABLE_NOT_LOCKED
+select * from t3;
+--error ER_TABLE_NOT_LOCKED_FOR_WRITE
+insert into t1 (a) values (1);
+--error ER_TABLE_NOT_LOCKED_FOR_WRITE
+insert into t2 (a) values (1);
+--error ER_TABLE_NOT_LOCKED
+insert into t3 (a) values (1);
+--error ER_NO_SUCH_TABLE
+lock table no_such_table read;
+--echo #
+--echo # We implicitly left the locked tables
+--echo # mode but still have the read lock.
+--echo # 
+--error ER_CANT_UPDATE_WITH_READLOCK
+insert into t2 (a) values (1);
+unlock tables;
+insert into t1 (a) values (1);
+insert into t2 (a) values (1);
+flush table t1, t2 with read lock;
+select * from t1;
+select * from t2;
+--error ER_TABLE_NOT_LOCKED
+select * from t3;
+--error ER_TABLE_NOT_LOCKED_FOR_WRITE
+insert into t1 (a) values (2);
+--error ER_TABLE_NOT_LOCKED_FOR_WRITE
+insert into t2 (a) values (2);
+--error ER_TABLE_NOT_LOCKED
+insert into t3 (a) values (2);
+--error ER_NO_SUCH_TABLE
+lock table no_such_table read;
+insert into t3 (a) values (2);
+
+
+--echo # 
+--echo # III. Concurrent tests.
+--echo #
+connect (con1,localhost,root,,);
+--echo # --> connection default
+--echo #
+--echo # Check that flush tables <list> with read lock
+--echo # does not affect non-locked tables.
+connection default;
+--echo #
+flush tables t1 with read lock;
+--echo # --> connection con1;
+connection con1;
+select * from t1;
+select * from t2;
+insert into t2 (a) values (3);
+--echo # --> connection default;
+connection default;
+unlock tables;
+--echo # --> connection con1
+connection con1;
+disconnect con1;
+--source include/wait_until_disconnected.inc
+connection default;
+drop table t1, t2, t3;
diff --git a/mysys/thr_rwlock.c b/mysys/thr_rwlock.c
index 0aa4d3fc3c4..2ac4a00695e 100644
--- a/mysys/thr_rwlock.c
+++ b/mysys/thr_rwlock.c
@@ -16,7 +16,8 @@
 /* Synchronization - readers / writer thread locks */
 
 #include "mysys_priv.h"
-#if defined(THREAD) && !defined(HAVE_PTHREAD_RWLOCK_RDLOCK) && !defined(HAVE_RWLOCK_INIT)
+#if defined(THREAD)
+#if defined(NEED_MY_RW_LOCK)
 #include <errno.h>
 
 /*
@@ -58,7 +59,7 @@
 *  Mountain View, California  94043
 */
 
-int my_rwlock_init(rw_lock_t *rwp, void *arg __attribute__((unused)))
+int my_rw_init(my_rw_lock_t *rwp, my_bool *prefer_readers_attr)
 {
   pthread_condattr_t	cond_attr;
 
@@ -70,12 +71,14 @@ int my_rwlock_init(rw_lock_t *rwp, void *arg __attribute__((unused)))
 
   rwp->state	= 0;
   rwp->waiters	= 0;
+  /* If attribute argument is NULL use default value - prefer writers. */
+  rwp->prefer_readers= prefer_readers_attr ? *prefer_readers_attr : FALSE;
 
   return(0);
 }
 
 
-int my_rwlock_destroy(rw_lock_t *rwp)
+int my_rw_destroy(my_rw_lock_t *rwp)
 {
   pthread_mutex_destroy( &rwp->lock );
   pthread_cond_destroy( &rwp->readers );
@@ -84,12 +87,13 @@ int my_rwlock_destroy(rw_lock_t *rwp)
 }
 
 
-int my_rw_rdlock(rw_lock_t *rwp)
+int my_rw_rdlock(my_rw_lock_t *rwp)
 {
   pthread_mutex_lock(&rwp->lock);
 
   /* active or queued writers */
-  while (( rwp->state < 0 ) || rwp->waiters)
+  while (( rwp->state < 0 ) ||
+         (rwp->waiters && ! rwp->prefer_readers))
     pthread_cond_wait( &rwp->readers, &rwp->lock);
 
   rwp->state++;
@@ -97,11 +101,12 @@ int my_rw_rdlock(rw_lock_t *rwp)
   return(0);
 }
 
-int my_rw_tryrdlock(rw_lock_t *rwp)
+int my_rw_tryrdlock(my_rw_lock_t *rwp)
 {
   int res;
   pthread_mutex_lock(&rwp->lock);
-  if ((rwp->state < 0 ) || rwp->waiters)
+  if ((rwp->state < 0 ) ||
+      (rwp->waiters && ! rwp->prefer_readers))
     res= EBUSY;					/* Can't get lock */
   else
   {
@@ -113,7 +118,7 @@ int my_rw_tryrdlock(rw_lock_t *rwp)
 }
 
 
-int my_rw_wrlock(rw_lock_t *rwp)
+int my_rw_wrlock(my_rw_lock_t *rwp)
 {
   pthread_mutex_lock(&rwp->lock);
   rwp->waiters++;				/* another writer queued */
@@ -127,7 +132,7 @@ int my_rw_wrlock(rw_lock_t *rwp)
 }
 
 
-int my_rw_trywrlock(rw_lock_t *rwp)
+int my_rw_trywrlock(my_rw_lock_t *rwp)
 {
   int res;
   pthread_mutex_lock(&rwp->lock);
@@ -143,7 +148,7 @@ int my_rw_trywrlock(rw_lock_t *rwp)
 }
 
 
-int my_rw_unlock(rw_lock_t *rwp)
+int my_rw_unlock(my_rw_lock_t *rwp)
 {
   DBUG_PRINT("rw_unlock",
 	     ("state: %d waiters: %d", rwp->state, rwp->waiters));
@@ -160,7 +165,8 @@ int my_rw_unlock(rw_lock_t *rwp)
   }
   else
   {
-    if ( --rwp->state == 0 )	/* no more readers */
+    if ( --rwp->state == 0 &&   /* no more readers */
+        rwp->waiters)
       pthread_cond_signal( &rwp->writers );
   }
 
@@ -168,4 +174,30 @@ int my_rw_unlock(rw_lock_t *rwp)
   return(0);
 }
 
-#endif
+
+int rw_pr_init(struct st_my_rw_lock_t *rwlock)
+{
+  my_bool prefer_readers_attr= TRUE;
+  return my_rw_init(rwlock, &prefer_readers_attr);
+}
+
+#else
+
+/*
+  We are on system which has native read/write locks which support
+  preferring of readers.
+*/
+
+int rw_pr_init(rw_pr_lock_t *rwlock)
+{
+  pthread_rwlockattr_t rwlock_attr;
+
+  pthread_rwlockattr_init(&rwlock_attr);
+  pthread_rwlockattr_setkind_np(&rwlock_attr, PTHREAD_RWLOCK_PREFER_READER_NP);
+  pthread_rwlock_init(rwlock, NULL);
+  pthread_rwlockattr_destroy(&rwlock_attr);
+  return 0;
+}
+
+#endif /* defined(NEED_MY_RW_LOCK) */
+#endif /* defined(THREAD) */
diff --git a/scripts/mysqlhotcopy.sh b/scripts/mysqlhotcopy.sh
index 21fca0c0848..90f759739d0 100644
--- a/scripts/mysqlhotcopy.sh
+++ b/scripts/mysqlhotcopy.sh
@@ -56,6 +56,8 @@ Usage: $0 db_name[./table_regex/] [new_db_name | directory]
   -h, --host=#         hostname for local server when connecting over TCP/IP
   -P, --port=#         port to use when connecting to local server with TCP/IP
   -S, --socket=#       socket to use when connecting to local server
+      --old_server     connect to old MySQL-server (before v5.5) which
+                       doesn't have FLUSH TABLES WITH READ LOCK fully implemented.
 
   --allowold           don\'t abort if target dir already exists (rename it _old)
   --addtodest          don\'t rename target dir if it exists, just add files to it
@@ -103,6 +105,7 @@ GetOptions( \%opt,
     "password|p=s",
     "port|P=s",
     "socket|S=s",
+    "old_server",
     "allowold!",
     "keepold!",
     "addtodest!",
@@ -441,21 +444,37 @@ if ( $opt{checkpoint} || $opt{record_log_pos} ) {
 my $hc_started = time;	# count from time lock is granted
 
 if ( $opt{dryrun} ) {
-    print "LOCK TABLES $hc_locks\n";
-    print "FLUSH TABLES /*!32323 $hc_tables */\n";
+    if ( $opt{old_server} ) {
+        print "LOCK TABLES $hc_locks\n";
+        print "FLUSH TABLES /*!32323 $hc_tables */\n";
+    }
+    else {
+        print "FLUSH TABLES $hc_tables WITH READ LOCK\n";
+    }
+    
     print "FLUSH LOGS\n" if ( $opt{flushlog} );
     print "RESET MASTER\n" if ( $opt{resetmaster} );
     print "RESET SLAVE\n" if ( $opt{resetslave} );
 }
 else {
     my $start = time;
-    $dbh->do("LOCK TABLES $hc_locks");
-    printf "Locked $num_tables tables in %d seconds.\n", time-$start unless $opt{quiet};
-    $hc_started = time;	# count from time lock is granted
+    if ( $opt{old_server} ) {
+        $dbh->do("LOCK TABLES $hc_locks");
+        printf "Locked $num_tables tables in %d seconds.\n", time-$start unless $opt{quiet};
+        $hc_started = time;	# count from time lock is granted
 
-    # flush tables to make on-disk copy up to date
-    $start = time;
-    $dbh->do("FLUSH TABLES /*!32323 $hc_tables */");
+        # flush tables to make on-disk copy up to date
+        $start = time;
+        $dbh->do("FLUSH TABLES /*!32323 $hc_tables */");
+    }
+    else {
+        $dbh->do("FLUSH TABLES $hc_tables WITH READ LOCK");
+        printf "Locked $num_tables tables in %d seconds.\n", time-$start unless $opt{quiet};
+        $hc_started = time;	# count from time lock is granted
+
+        # flush tables to make on-disk copy up to date
+        $start = time;
+    }
     printf "Flushed tables ($hc_tables) in %d seconds.\n", time-$start unless $opt{quiet};
     $dbh->do( "FLUSH LOGS" ) if ( $opt{flushlog} );
     $dbh->do( "RESET MASTER" ) if ( $opt{resetmaster} );
@@ -975,6 +994,10 @@ when using the --host option.
 
 UNIX domain socket to use when connecting to local server.
 
+=item --old_server
+
+Use old server (pre v5.5) commands.
+
 =item  --noindices          
 
 Don\'t include index files in copy. Only up to the first 2048 bytes
diff --git a/sql/mdl.cc b/sql/mdl.cc
index 28cff420e0d..f9a4e10aade 100644
--- a/sql/mdl.cc
+++ b/sql/mdl.cc
@@ -148,10 +148,37 @@ public:
   /**
     Read-write lock protecting this lock context.
 
-    TODO/FIXME: Replace with RW-lock which will prefer readers
-                on all platforms and not only on Linux.
+    @note The fact that we use read-write lock prefers readers here is
+          important as deadlock detector won't work correctly otherwise.
+
+          For example, imagine that we have following waiters graph:
+
+                       ctxA -> obj1 -> ctxB -> obj1 -|
+                        ^                            |
+                        |----------------------------|
+
+          and both ctxA and ctxB start deadlock detection process:
+
+            ctxA read-locks obj1             ctxB read-locks obj2
+            ctxA goes deeper                 ctxB goes deeper
+
+          Now ctxC comes in who wants to start waiting on obj1, also
+          ctxD comes in who wants to start waiting on obj2.
+
+            ctxC tries to write-lock obj1   ctxD tries to write-lock obj2
+            ctxC is blocked                 ctxD is blocked
+
+          Now ctxA and ctxB resume their search:
+
+            ctxA tries to read-lock obj2    ctxB tries to read-lock obj1
+
+          If m_rwlock prefers writes (or fair) both ctxA and ctxB would be
+          blocked because of pending write locks from ctxD and ctxC
+          correspondingly. Thus we will get a deadlock in deadlock detector.
+          If m_wrlock prefers readers (actually ignoring pending writers is
+          enough) ctxA and ctxB will continue and no deadlock will occur.
   */
-  rw_lock_t m_rwlock;
+  rw_pr_lock_t m_rwlock;
 
   bool is_empty() const
   {
@@ -213,12 +240,12 @@ public:
     m_ref_release(0),
     m_is_destroyed(FALSE)
   {
-    my_rwlock_init(&m_rwlock, NULL);
+    rw_pr_init(&m_rwlock);
   }
 
   virtual ~MDL_lock()
   {
-    rwlock_destroy(&m_rwlock);
+    rw_pr_destroy(&m_rwlock);
   }
   inline static void destroy(MDL_lock *lock);
 public:
@@ -480,7 +507,7 @@ bool MDL_map::move_from_hash_to_lock_mutex(MDL_lock *lock)
   lock->m_ref_usage++;
   mysql_mutex_unlock(&m_mutex);
 
-  rw_wrlock(&lock->m_rwlock);
+  rw_pr_wrlock(&lock->m_rwlock);
   lock->m_ref_release++;
   if (unlikely(lock->m_is_destroyed))
   {
@@ -495,7 +522,7 @@ bool MDL_map::move_from_hash_to_lock_mutex(MDL_lock *lock)
     */
     uint ref_usage= lock->m_ref_usage;
     uint ref_release= lock->m_ref_release;
-    rw_unlock(&lock->m_rwlock);
+    rw_pr_unlock(&lock->m_rwlock);
     if (ref_usage == ref_release)
       MDL_lock::destroy(lock);
     return TRUE;
@@ -538,7 +565,7 @@ void MDL_map::remove(MDL_lock *lock)
   lock->m_is_destroyed= TRUE;
   ref_usage= lock->m_ref_usage;
   ref_release= lock->m_ref_release;
-  rw_unlock(&lock->m_rwlock);
+  rw_pr_unlock(&lock->m_rwlock);
   mysql_mutex_unlock(&m_mutex);
   if (ref_usage == ref_release)
     MDL_lock::destroy(lock);
@@ -559,7 +586,7 @@ MDL_context::MDL_context()
   m_deadlock_weight(0),
   m_signal(NO_WAKE_UP)
 {
-  my_rwlock_init(&m_waiting_for_lock, NULL);
+  rw_pr_init(&m_waiting_for_lock);
   mysql_mutex_init(NULL /* pfs key */, &m_signal_lock, NULL);
   mysql_cond_init(NULL /* pfs key */, &m_signal_cond, NULL);
 }
@@ -581,7 +608,7 @@ void MDL_context::destroy()
 {
   DBUG_ASSERT(m_tickets.is_empty());
 
-  rwlock_destroy(&m_waiting_for_lock);
+  rw_pr_destroy(&m_waiting_for_lock);
   mysql_mutex_destroy(&m_signal_lock);
   mysql_cond_destroy(&m_signal_cond);
 }
@@ -1071,7 +1098,7 @@ MDL_lock::can_grant_lock(enum_mdl_type type_arg,
 
 void MDL_lock::remove_ticket(Ticket_list MDL_lock::*list, MDL_ticket *ticket)
 {
-  rw_wrlock(&m_rwlock);
+  rw_pr_wrlock(&m_rwlock);
   (this->*list).remove_ticket(ticket);
   if (is_empty())
     mdl_locks.remove(this);
@@ -1082,7 +1109,7 @@ void MDL_lock::remove_ticket(Ticket_list MDL_lock::*list, MDL_ticket *ticket)
       which now might be able to do it. Wake them up!
     */
     wake_up_waiters();
-    rw_unlock(&m_rwlock);
+    rw_pr_unlock(&m_rwlock);
   }
 }
 
@@ -1102,9 +1129,9 @@ bool MDL_lock::has_pending_conflicting_lock(enum_mdl_type type)
 
   mysql_mutex_assert_not_owner(&LOCK_open);
 
-  rw_rdlock(&m_rwlock);
+  rw_pr_rdlock(&m_rwlock);
   result= (m_waiting.bitmap() & incompatible_granted_types_bitmap()[type]);
-  rw_unlock(&m_rwlock);
+  rw_pr_unlock(&m_rwlock);
   return result;
 }
 
@@ -1298,7 +1325,7 @@ MDL_context::try_acquire_lock(MDL_request *mdl_request)
   {
     ticket->m_lock= lock;
     lock->m_granted.add_ticket(ticket);
-    rw_unlock(&lock->m_rwlock);
+    rw_pr_unlock(&lock->m_rwlock);
 
     m_tickets.push_front(ticket);
 
@@ -1308,7 +1335,7 @@ MDL_context::try_acquire_lock(MDL_request *mdl_request)
   {
     /* We can't get here if we allocated a new lock. */
     DBUG_ASSERT(! lock->is_empty());
-    rw_unlock(&lock->m_rwlock);
+    rw_pr_unlock(&lock->m_rwlock);
     MDL_ticket::destroy(ticket);
   }
 
@@ -1349,9 +1376,9 @@ MDL_context::clone_ticket(MDL_request *mdl_request)
   ticket->m_lock= mdl_request->ticket->m_lock;
   mdl_request->ticket= ticket;
 
-  rw_wrlock(&ticket->m_lock->m_rwlock);
+  rw_pr_wrlock(&ticket->m_lock->m_rwlock);
   ticket->m_lock->m_granted.add_ticket(ticket);
-  rw_unlock(&ticket->m_lock->m_rwlock);
+  rw_pr_unlock(&ticket->m_lock->m_rwlock);
 
   m_tickets.push_front(ticket);
 
@@ -1457,7 +1484,7 @@ bool MDL_context::acquire_lock_impl(MDL_request *mdl_request,
     if (ticket->is_upgradable_or_exclusive())
       lock->notify_shared_locks(this);
 
-    rw_unlock(&lock->m_rwlock);
+    rw_pr_unlock(&lock->m_rwlock);
 
     set_deadlock_weight(mdl_request->get_deadlock_weight());
     will_wait_for(ticket);
@@ -1492,7 +1519,7 @@ bool MDL_context::acquire_lock_impl(MDL_request *mdl_request,
         my_error(ER_LOCK_WAIT_TIMEOUT, MYF(0));
       return TRUE;
     }
-    rw_wrlock(&lock->m_rwlock);
+    rw_pr_wrlock(&lock->m_rwlock);
   }
 
   lock->m_waiting.remove_ticket(ticket);
@@ -1502,7 +1529,7 @@ bool MDL_context::acquire_lock_impl(MDL_request *mdl_request,
     (*lock->cached_object_release_hook)(lock->cached_object);
   lock->cached_object= NULL;
 
-  rw_unlock(&lock->m_rwlock);
+  rw_pr_unlock(&lock->m_rwlock);
 
   m_tickets.push_front(ticket);
 
@@ -1647,7 +1674,7 @@ MDL_context::upgrade_shared_lock_to_exclusive(MDL_ticket *mdl_ticket,
   is_new_ticket= ! has_lock(mdl_svp, mdl_xlock_request.ticket);
 
   /* Merge the acquired and the original lock. @todo: move to a method. */
-  rw_wrlock(&mdl_ticket->m_lock->m_rwlock);
+  rw_pr_wrlock(&mdl_ticket->m_lock->m_rwlock);
   if (is_new_ticket)
     mdl_ticket->m_lock->m_granted.remove_ticket(mdl_xlock_request.ticket);
   /*
@@ -1659,7 +1686,7 @@ MDL_context::upgrade_shared_lock_to_exclusive(MDL_ticket *mdl_ticket,
   mdl_ticket->m_type= MDL_EXCLUSIVE;
   mdl_ticket->m_lock->m_granted.add_ticket(mdl_ticket);
 
-  rw_unlock(&mdl_ticket->m_lock->m_rwlock);
+  rw_pr_unlock(&mdl_ticket->m_lock->m_rwlock);
 
   if (is_new_ticket)
   {
@@ -1677,7 +1704,7 @@ bool MDL_lock::find_deadlock(MDL_ticket *waiting_ticket,
   MDL_ticket *ticket;
   bool result= FALSE;
 
-  rw_rdlock(&m_rwlock);
+  rw_pr_rdlock(&m_rwlock);
 
   Ticket_iterator granted_it(m_granted);
   Ticket_iterator waiting_it(m_waiting);
@@ -1729,7 +1756,7 @@ bool MDL_lock::find_deadlock(MDL_ticket *waiting_ticket,
   }
 
 end:
-  rw_unlock(&m_rwlock);
+  rw_pr_unlock(&m_rwlock);
   return result;
 }
 
@@ -1738,7 +1765,7 @@ bool MDL_context::find_deadlock(Deadlock_detection_context *deadlock_ctx)
 {
   bool result= FALSE;
 
-  rw_rdlock(&m_waiting_for_lock);
+  rw_pr_rdlock(&m_waiting_for_lock);
 
   if (m_waiting_for)
   {
@@ -1767,14 +1794,14 @@ bool MDL_context::find_deadlock(Deadlock_detection_context *deadlock_ctx)
       deadlock_ctx->victim= this;
     else if (deadlock_ctx->victim->m_deadlock_weight >= m_deadlock_weight)
     {
-      rw_unlock(&deadlock_ctx->victim->m_waiting_for_lock);
+      rw_pr_unlock(&deadlock_ctx->victim->m_waiting_for_lock);
       deadlock_ctx->victim= this;
     }
     else
-      rw_unlock(&m_waiting_for_lock);
+      rw_pr_unlock(&m_waiting_for_lock);
   }
   else
-    rw_unlock(&m_waiting_for_lock);
+    rw_pr_unlock(&m_waiting_for_lock);
 
   return result;
 }
@@ -1800,7 +1827,7 @@ bool MDL_context::find_deadlock()
     if (deadlock_ctx.victim != this)
     {
       deadlock_ctx.victim->awake(VICTIM_WAKE_UP);
-      rw_unlock(&deadlock_ctx.victim->m_waiting_for_lock);
+      rw_pr_unlock(&deadlock_ctx.victim->m_waiting_for_lock);
       /*
         After adding new arc to waiting graph we found that it participates
         in some loop (i.e. there is a deadlock). We decided to destroy this
@@ -1813,7 +1840,7 @@ bool MDL_context::find_deadlock()
     else
     {
       DBUG_ASSERT(&deadlock_ctx.victim->m_waiting_for_lock == &m_waiting_for_lock);
-      rw_unlock(&deadlock_ctx.victim->m_waiting_for_lock);
+      rw_pr_unlock(&deadlock_ctx.victim->m_waiting_for_lock);
       return TRUE;
     }
   }
@@ -1870,14 +1897,14 @@ MDL_context::wait_for_lock(MDL_request *mdl_request, ulong lock_wait_timeout)
 
     if (lock->can_grant_lock(mdl_request->type, this))
     {
-      rw_unlock(&lock->m_rwlock);
+      rw_pr_unlock(&lock->m_rwlock);
       return FALSE;
     }
 
     MDL_ticket *pending_ticket;
     if (! (pending_ticket= MDL_ticket::create(this, mdl_request->type)))
     {
-      rw_unlock(&lock->m_rwlock);
+      rw_pr_unlock(&lock->m_rwlock);
       return TRUE;
     }
 
@@ -1886,7 +1913,7 @@ MDL_context::wait_for_lock(MDL_request *mdl_request, ulong lock_wait_timeout)
     lock->m_waiting.add_ticket(pending_ticket);
 
     wait_reset();
-    rw_unlock(&lock->m_rwlock);
+    rw_pr_unlock(&lock->m_rwlock);
 
     set_deadlock_weight(MDL_DEADLOCK_WEIGHT_DML);
     will_wait_for(pending_ticket);
@@ -2037,7 +2064,7 @@ void MDL_ticket::downgrade_exclusive_lock(enum_mdl_type type)
   if (m_type != MDL_EXCLUSIVE)
     return;
 
-  rw_wrlock(&m_lock->m_rwlock);
+  rw_pr_wrlock(&m_lock->m_rwlock);
   /*
     To update state of MDL_lock object correctly we need to temporarily
     exclude ticket from the granted queue and then include it back.
@@ -2046,7 +2073,7 @@ void MDL_ticket::downgrade_exclusive_lock(enum_mdl_type type)
   m_type= type;
   m_lock->m_granted.add_ticket(this);
   m_lock->wake_up_waiters();
-  rw_unlock(&m_lock->m_rwlock);
+  rw_pr_unlock(&m_lock->m_rwlock);
 }
 
 
diff --git a/sql/mdl.h b/sql/mdl.h
index 59bc1f64762..42461f6ac2f 100644
--- a/sql/mdl.h
+++ b/sql/mdl.h
@@ -624,10 +624,11 @@ private:
   /**
     Read-write lock protecting m_waiting_for member.
 
-    TODO/FIXME: Replace with RW-lock which will prefer readers
-                on all platforms and not only on Linux.
+    @note The fact that this read-write lock prefers readers is
+          important as deadlock detector won't work correctly
+          otherwise. @sa Comment for MDL_lock::m_rwlock.
   */
-  rw_lock_t m_waiting_for_lock;
+  rw_pr_lock_t m_waiting_for_lock;
   MDL_ticket *m_waiting_for;
   uint m_deadlock_weight;
   /**
@@ -651,9 +652,9 @@ private:
 
   void will_wait_for(MDL_ticket *pending_ticket)
   {
-    rw_wrlock(&m_waiting_for_lock);
+    rw_pr_wrlock(&m_waiting_for_lock);
     m_waiting_for= pending_ticket;
-    rw_unlock(&m_waiting_for_lock);
+    rw_pr_unlock(&m_waiting_for_lock);
   }
 
   void set_deadlock_weight(uint weight)
@@ -669,9 +670,9 @@ private:
 
   void stop_waiting()
   {
-    rw_wrlock(&m_waiting_for_lock);
+    rw_pr_wrlock(&m_waiting_for_lock);
     m_waiting_for= NULL;
-    rw_unlock(&m_waiting_for_lock);
+    rw_pr_unlock(&m_waiting_for_lock);
   }
 
   void wait_reset()
diff --git a/sql/mysql_priv.h b/sql/mysql_priv.h
index 20720d50194..d5df0ab5930 100644
--- a/sql/mysql_priv.h
+++ b/sql/mysql_priv.h
@@ -1965,7 +1965,8 @@ extern ulong slow_launch_threads, slow_launch_time;
 extern ulong table_cache_size, table_def_size;
 extern MYSQL_PLUGIN_IMPORT ulong max_connections;
 extern ulong max_connect_errors, connect_timeout;
-extern ulong slave_net_timeout, slave_trans_retries;
+extern ulong slave_trans_retries;
+extern uint  slave_net_timeout;
 extern ulong what_to_log,flush_time;
 extern ulong query_buff_size;
 extern ulong max_prepared_stmt_count, prepared_stmt_count;
diff --git a/sql/mysqld.cc b/sql/mysqld.cc
index 6bd133660b3..41563db4abb 100644
--- a/sql/mysqld.cc
+++ b/sql/mysqld.cc
@@ -464,7 +464,8 @@ ulong table_cache_size, table_def_size;
 ulong what_to_log;
 ulong query_buff_size, slow_launch_time, slave_open_temp_tables;
 ulong open_files_limit, max_binlog_size, max_relay_log_size;
-ulong slave_net_timeout, slave_trans_retries;
+ulong slave_trans_retries;
+uint  slave_net_timeout;
 uint slave_exec_mode_options;
 ulonglong slave_type_conversions_options;
 ulong thread_cache_size=0, thread_pool_size= 0;
diff --git a/sql/sql_parse.cc b/sql/sql_parse.cc
index e66f2756c54..7a13c46e4f6 100644
--- a/sql/sql_parse.cc
+++ b/sql/sql_parse.cc
@@ -1587,6 +1587,113 @@ int prepare_schema_table(THD *thd, LEX *lex, Table_ident *table_ident,
 }
 
 
+/**
+  Implementation of FLUSH TABLES <table_list> WITH READ LOCK.
+
+  In brief: take exclusive locks, expel tables from the table
+  cache, reopen the tables, enter the 'LOCKED TABLES' mode,
+  downgrade the locks.
+
+  Required privileges
+  -------------------
+  Since the statement implicitly enters LOCK TABLES mode,
+  it requires LOCK TABLES privilege on every table.
+  But since the rest of FLUSH commands require
+  the global RELOAD_ACL, it also requires RELOAD_ACL.
+
+  Compatibility with the global read lock
+  ---------------------------------------
+  We don't wait for the GRL, since neither the
+  5.1 combination that this new statement is intended to
+  replace (LOCK TABLE <list> WRITE; FLUSH TABLES;),
+  nor FLUSH TABLES WITH READ LOCK do.
+  @todo: this is not implemented, Dmitry disagrees.
+  Currently we wait for GRL in another connection,
+  but are compatible with a GRL in our own connection.
+
+  Behaviour under LOCK TABLES
+  ---------------------------
+  Bail out: i.e. don't perform an implicit UNLOCK TABLES.
+  This is not consistent with LOCK TABLES statement, but is
+  in line with behaviour of FLUSH TABLES WITH READ LOCK, and we
+  try to not introduce any new statements with implicit
+  semantics.
+
+  Compatibility with parallel updates
+  -----------------------------------
+  As a result, we will wait for all open transactions
+  against the tables to complete. After the lock downgrade,
+  new transactions will be able to read the tables, but not
+  write to them.
+
+  Differences from FLUSH TABLES <list>
+  -------------------------------------
+  - you can't flush WITH READ LOCK a non-existent table
+  - you can't flush WITH READ LOCK under LOCK TABLES
+  - currently incompatible with the GRL (@todo: fix)
+*/
+
+static bool flush_tables_with_read_lock(THD *thd, TABLE_LIST *all_tables)
+{
+  Lock_tables_prelocking_strategy lock_tables_prelocking_strategy;
+  TABLE_LIST *table_list;
+
+  /*
+    This is called from SQLCOM_FLUSH, the transaction has
+    been committed implicitly.
+  */
+
+  /* RELOAD_ACL is checked by the caller. Check table-level privileges. */
+  if (check_table_access(thd, LOCK_TABLES_ACL | SELECT_ACL, all_tables,
+                         FALSE, UINT_MAX, FALSE))
+    goto error;
+
+  if (thd->locked_tables_mode)
+  {
+    my_error(ER_LOCK_OR_ACTIVE_TRANSACTION, MYF(0));
+    goto error;
+  }
+
+  /*
+    @todo: Since lock_table_names() acquires a global IX
+    lock, this actually waits for a GRL in another connection.
+    We are thus introducing an incompatibility.
+    Do nothing for now, since not taking a global IX violates
+    current internal MDL asserts, fix after discussing with
+    Dmitry.
+  */
+  if (lock_table_names(thd, all_tables))
+    goto error;
+
+  if  (open_and_lock_tables(thd, all_tables, FALSE,
+                            MYSQL_OPEN_HAS_MDL_LOCK,
+                            &lock_tables_prelocking_strategy) ||
+       thd->locked_tables_list.init_locked_tables(thd))
+  {
+    close_thread_tables(thd);
+    goto error;
+  }
+
+  /*
+    Downgrade the exclusive locks.
+    Use MDL_SHARED_NO_WRITE as the intended
+    post effect of this call is identical
+    to LOCK TABLES <...> READ, and we didn't use
+    thd->in_lock_talbes and thd->sql_command= SQLCOM_LOCK_TABLES
+    hacks to enter the LTM.
+    @todo: release the global IX lock here!!!
+  */
+  for (table_list= all_tables; table_list;
+       table_list= table_list->next_global)
+    table_list->mdl_request.ticket->downgrade_exclusive_lock(MDL_SHARED_NO_WRITE);
+
+  return FALSE;
+
+error:
+  return TRUE;
+}
+
+
 /**
   Read query from packet and store in thd->query.
   Used in COM_QUERY and COM_STMT_PREPARE.
@@ -3728,9 +3835,18 @@ end_with_restore_list:
   case SQLCOM_FLUSH:
   {
     bool write_to_binlog;
+
     if (check_global_access(thd,RELOAD_ACL))
       goto error;
 
+    if (first_table && lex->type & REFRESH_READ_LOCK)
+    {
+      if (flush_tables_with_read_lock(thd, all_tables))
+        goto error;
+      my_ok(thd);
+      break;
+    }
+
     /*
       reload_acl_and_cache() will tell us if we are allowed to write to the
       binlog or not.
diff --git a/sql/sql_yacc.yy b/sql/sql_yacc.yy
index f03694cb359..5648e3cbdb5 100644
--- a/sql/sql_yacc.yy
+++ b/sql/sql_yacc.yy
@@ -767,10 +767,10 @@ bool my_yyoverflow(short **a, YYSTYPE **b, ulong *yystacksize);
 
 %pure_parser                                    /* We have threads */
 /*
-  Currently there are 169 shift/reduce conflicts.
+  Currently there are 168 shift/reduce conflicts.
   We should not introduce new conflicts any more.
 */
-%expect 169
+%expect 168
 
 /*
    Comments for TOKENS.
@@ -1554,6 +1554,7 @@ bool my_yyoverflow(short **a, YYSTYPE **b, ulong *yystacksize);
         opt_column_list grant_privileges grant_ident grant_list grant_option
         object_privilege object_privilege_list user_list rename_list
         clear_privileges flush_options flush_option
+        opt_with_read_lock flush_options_list
         equal optional_braces
         opt_mi_check_type opt_to mi_check_types normal_join
         table_to_table_list table_to_table opt_table_list opt_as
@@ -11095,17 +11096,27 @@ flush:
         ;
 
 flush_options:
-          flush_options ',' flush_option
-        | flush_option
-        ;
-
-flush_option:
           table_or_tables
           { Lex->type|= REFRESH_TABLES; }
           opt_table_list {}
-        | TABLES WITH READ_SYM LOCK_SYM
-          { Lex->type|= REFRESH_TABLES | REFRESH_READ_LOCK; }
-        | ERROR_SYM LOGS_SYM
+          opt_with_read_lock {}
+        | flush_options_list
+        ;
+
+opt_with_read_lock:
+          /* empty */ {}
+        | WITH READ_SYM LOCK_SYM
+          { Lex->type|= REFRESH_READ_LOCK; }
+        ;
+
+flush_options_list:
+          flush_options_list ',' flush_option
+        | flush_option
+          {}
+        ;
+
+flush_option:
+          ERROR_SYM LOGS_SYM
           { Lex->type|= REFRESH_ERROR_LOG; }
         | ENGINE_SYM LOGS_SYM
           { Lex->type|= REFRESH_ENGINE_LOG; } 
diff --git a/sql/sys_vars.cc b/sql/sys_vars.cc
index ba970925fc6..80eee89c8a9 100644
--- a/sql/sys_vars.cc
+++ b/sql/sys_vars.cc
@@ -1305,6 +1305,17 @@ static Sys_var_ulong Sys_optimizer_prune_level(
        SESSION_VAR(optimizer_prune_level), CMD_LINE(REQUIRED_ARG),
        VALID_RANGE(0, 1), DEFAULT(1), BLOCK_SIZE(1));
 
+/** Warns about deprecated value 63 */
+static bool fix_optimizer_search_depth(sys_var *self, THD *thd,
+                                       enum_var_type type)
+{
+  SV *sv= type == OPT_GLOBAL ? &global_system_variables : &thd->variables;
+  if (sv->optimizer_search_depth == MAX_TABLES+2)
+    WARN_DEPRECATED(thd, 6, 0, "optimizer-search-depth=63",
+                    "a search depth less than 63");
+  return false;
+}
+
 static Sys_var_ulong Sys_optimizer_search_depth(
        "optimizer_search_depth",
        "Maximum depth of search performed by the query optimizer. Values "
@@ -1313,10 +1324,12 @@ static Sys_var_ulong Sys_optimizer_search_depth(
        "than the number of tables in a relation result in faster "
        "optimization, but may produce very bad query plans. If set to 0, "
        "the system will automatically pick a reasonable value; if set to "
-       "63, the optimizer will switch to the original find_best search"
-       "(used for testing/comparison)",
+       "63, the optimizer will switch to the original find_best search. "
+       "NOTE: The value 63 and its associated behaviour is deprecated",
        SESSION_VAR(optimizer_search_depth), CMD_LINE(REQUIRED_ARG),
-       VALID_RANGE(0, MAX_TABLES+2), DEFAULT(MAX_TABLES+1), BLOCK_SIZE(1));
+       VALID_RANGE(0, MAX_TABLES+2), DEFAULT(MAX_TABLES+1), BLOCK_SIZE(1),
+       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
+       ON_UPDATE(fix_optimizer_search_depth));
 
 static const char *optimizer_switch_names[]=
 {
@@ -2795,7 +2808,7 @@ static bool fix_slave_net_timeout(sys_var *self, THD *thd, enum_var_type type)
   mysql_mutex_unlock(&LOCK_active_mi);
   return false;
 }
-static Sys_var_ulong Sys_slave_net_timeout(
+static Sys_var_uint Sys_slave_net_timeout(
        "slave_net_timeout", "Number of seconds to wait for more data "
        "from a master/slave connection before aborting the read",
        GLOBAL_VAR(slave_net_timeout), CMD_LINE(REQUIRED_ARG),
diff --git a/storage/perfschema/pfs_instr.cc b/storage/perfschema/pfs_instr.cc
index 2ce3a844290..28b54cc6979 100644
--- a/storage/perfschema/pfs_instr.cc
+++ b/storage/perfschema/pfs_instr.cc
@@ -66,7 +66,7 @@ ulong events_waits_history_per_thread;
 /** Number of instruments class per thread. */
 ulong instr_class_per_thread;
 /** Number of locker lost. @sa LOCKER_STACK_SIZE. */
-ulong locker_lost;
+ulong locker_lost= 0;
 
 /**
   Mutex instrumentation instances array.
@@ -746,8 +746,23 @@ find_or_create_file(PFS_thread *thread, PFS_file_class *klass,
     }
   }
 
-  if (len >= sizeof(pfs->m_filename))
-    len= sizeof(pfs->m_filename) - 1;
+  /*
+    Normalize the file name to avoid duplicates when using aliases:
+    - absolute or relative paths
+    - symbolic links
+  */
+  char buffer[FN_REFLEN];
+  const char *normalized_filename;
+  int normalized_length;
+
+  /*
+    Ignore errors, the file may not exist.
+    my_realpath always provide a best effort result in buffer.
+  */
+  (void) my_realpath(buffer, filename, MYF(0));
+
+  normalized_filename= buffer;
+  normalized_length= strlen(normalized_filename);
 
   PFS_file **entry;
   uint retry_count= 0;
@@ -755,7 +770,7 @@ find_or_create_file(PFS_thread *thread, PFS_file_class *klass,
 search:
   entry= reinterpret_cast<PFS_file**>
     (lf_hash_search(&filename_hash, thread->m_filename_hash_pins,
-                    filename, len));
+                    normalized_filename, normalized_length));
   if (entry && (entry != MY_ERRPTR))
   {
     pfs= *entry;
@@ -783,9 +798,9 @@ search:
         if (pfs->m_lock.free_to_dirty())
         {
           pfs->m_class= klass;
-          strncpy(pfs->m_filename, filename, len);
-          pfs->m_filename[len]= '\0';
-          pfs->m_filename_length= len;
+          strncpy(pfs->m_filename, normalized_filename, normalized_length);
+          pfs->m_filename[normalized_length]= '\0';
+          pfs->m_filename_length= normalized_length;
           pfs->m_file_stat.m_open_count= 1;
           pfs->m_wait_stat.m_control_flag=
             &flag_events_waits_summary_by_instance;