Maintain connection_count atomically

Removed LOCK_connection_count.

Removed duplicate denied_connections and connection_errors_max_connection
increment from create_new_thread(). Another increment done by
CONNECT::close_with_error().

Simplified away CONNECT::thread_count_incremented. Now close_with_error()
is always called with connection_count incremented.

Part of MDEV-19515 - Improve connect speed

include/thread_pool_priv.h

@@ -92,8 +92,6 @@ void mysql_audit_release(THD *thd);
 bool thd_is_connection_alive(THD *thd);
 /* Close connection with possible error code */
 void close_connection(THD *thd, uint errcode);
-/* Decrement connection counter */
-void dec_connection_count();
 /* Destroy THD object */
 void delete_thd(THD *thd);
 

mysql-test/suite/perfschema/include/event_aggregate_load.inc

@@ -27,9 +27,6 @@ execute dump_hosts;
 
 # Notes about this test
 #
-# Each connect causes 2 wait/synch/mutex/sql/LOCK_connection_count events:
-# - 1 in mysqld.cc, create_new_thread(), for the main thread
-# - 1 in sql_connect.cc, check_user(), for the connected thread
 # The main thread does not count for BY_ACCOUNT / BY_HOST.
 # The user thread does count for BY_ACCOUNT, BY_HOST
 #

mysql-test/suite/perfschema/include/event_aggregate_setup.inc

@@ -111,8 +111,7 @@ update performance_schema.threads set instrumented='NO';
 update performance_schema.setup_instruments set enabled='NO', timed='NO';
 
 update performance_schema.setup_instruments set enabled='YES', timed='YES'
-  where name in ('wait/synch/mutex/sql/LOCK_connection_count',
-                 'wait/synch/mutex/sql/LOCK_user_locks',
+  where name in ('wait/synch/mutex/sql/LOCK_user_locks',
                  'wait/synch/rwlock/sql/LOCK_grant',
                  'wait/io/file/sql/query_log',
                  'idle');
@@ -181,8 +180,7 @@ begin
   if (my_thread_id is not null) then
     select username, event_name, count_star
       from performance_schema.events_waits_summary_by_thread_by_event_name
-      where event_name in ('wait/synch/mutex/sql/LOCK_connection_count',
-                           'wait/synch/mutex/sql/LOCK_user_locks',
+      where event_name in ('wait/synch/mutex/sql/LOCK_user_locks',
                            'wait/synch/rwlock/sql/LOCK_grant',
                            'wait/io/file/sql/query_log')
       and thread_id = my_thread_id
@@ -199,8 +197,7 @@ prepare dump_waits_account from
   "select user, host, event_name, count_star
   from performance_schema.events_waits_summary_by_account_by_event_name
   where user like \'user%\'
-  and event_name in ('wait/synch/mutex/sql/LOCK_connection_count',
-                     'wait/synch/mutex/sql/LOCK_user_locks',
+  and event_name in ('wait/synch/mutex/sql/LOCK_user_locks',
                      'wait/synch/rwlock/sql/LOCK_grant',
                      'wait/io/file/sql/query_log')
   order by user, host, event_name;";
@@ -209,8 +206,7 @@ prepare dump_waits_user from
   "select user, event_name, count_star
   from performance_schema.events_waits_summary_by_user_by_event_name
   where user like \'user%\'
-  and event_name in ('wait/synch/mutex/sql/LOCK_connection_count',
-                     'wait/synch/mutex/sql/LOCK_user_locks',
+  and event_name in ('wait/synch/mutex/sql/LOCK_user_locks',
                      'wait/synch/rwlock/sql/LOCK_grant',
                      'wait/io/file/sql/query_log')
   order by user, event_name;";
@@ -219,8 +215,7 @@ prepare dump_waits_host from
   "select host, event_name, count_star
   from performance_schema.events_waits_summary_by_host_by_event_name
   where host=\'localhost\'
-  and event_name in ('wait/synch/mutex/sql/LOCK_connection_count',
-                     'wait/synch/mutex/sql/LOCK_user_locks',
+  and event_name in ('wait/synch/mutex/sql/LOCK_user_locks',
                      'wait/synch/rwlock/sql/LOCK_grant',
                      'wait/io/file/sql/query_log')
   order by host, event_name;";
@@ -228,8 +223,7 @@ prepare dump_waits_host from
 prepare dump_waits_global from
   "select event_name, count_star
   from performance_schema.events_waits_summary_global_by_event_name
-  where event_name in ('wait/synch/mutex/sql/LOCK_connection_count',
-                       'wait/synch/mutex/sql/LOCK_user_locks',
+  where event_name in ('wait/synch/mutex/sql/LOCK_user_locks',
                        'wait/synch/rwlock/sql/LOCK_grant',
                        'wait/io/file/sql/query_log')
   order by event_name;";
@@ -237,8 +231,7 @@ prepare dump_waits_global from
 prepare dump_waits_history from
   "select event_name, count(event_name)
   from performance_schema.events_waits_history_long
-  where event_name in ('wait/synch/mutex/sql/LOCK_connection_count',
-                       'wait/synch/mutex/sql/LOCK_user_locks',
+  where event_name in ('wait/synch/mutex/sql/LOCK_user_locks',
                        'wait/synch/rwlock/sql/LOCK_grant',
                        'wait/io/file/sql/query_log')
   group by event_name order by event_name;";

mysql-test/suite/perfschema/r/server_init.result

@@ -88,10 +88,6 @@ where name like "wait/synch/mutex/sql/LOCK_prepared_stmt_count";
 count(name)
 1
 select count(name) from mutex_instances
-where name like "wait/synch/mutex/sql/LOCK_connection_count";
-count(name)
-1
-select count(name) from mutex_instances
 where name like "wait/synch/mutex/sql/LOCK_server_started";
 count(name)
 1

mysql-test/suite/perfschema/t/server_init.test

@@ -85,9 +85,6 @@ select count(name) from mutex_instances
 select count(name) from mutex_instances
  where name like "wait/synch/mutex/sql/LOCK_prepared_stmt_count";
 
-select count(name) from mutex_instances
- where name like "wait/synch/mutex/sql/LOCK_connection_count";
-
 select count(name) from mutex_instances
  where name like "wait/synch/mutex/sql/LOCK_server_started";
 

sql/scheduler.cc

@@ -112,7 +112,7 @@ void post_kill_notification(THD *thd)
 
 void one_thread_per_connection_scheduler(scheduler_functions *func,
     ulong *arg_max_connections,
-    uint *arg_connection_count)
+    Atomic_counter<uint> *arg_connection_count)
 {
   scheduler_init();
   func->max_threads= *arg_max_connections + 1;