MDEV-5533 increase the default max thread pool size

500 -> 1000

mysql-test/r/mysqld--help,win.rdiff

@@ -122,7 +122,7 @@
  tc-heuristic-recover COMMIT
  thread-cache-size 0
 -thread-pool-idle-timeout 60
- thread-pool-max-threads 500
+ thread-pool-max-threads 1000
 -thread-pool-oversubscribe 3
 -thread-pool-stall-limit 500
 +thread-pool-min-threads 1

mysql-test/r/mysqld--help.result

@@ -1378,7 +1378,7 @@ table-open-cache 400
 tc-heuristic-recover COMMIT
 thread-cache-size 0
 thread-pool-idle-timeout 60
-thread-pool-max-threads 500
+thread-pool-max-threads 1000
 thread-pool-oversubscribe 3
 thread-pool-stall-limit 500
 thread-stack 294912

mysql-test/suite/sys_vars/r/sysvars_server_notembedded.result

@@ -4447,9 +4447,9 @@ READ_ONLY	NO
 COMMAND_LINE_ARGUMENT	REQUIRED
 VARIABLE_NAME	THREAD_POOL_MAX_THREADS
 SESSION_VALUE	NULL
-GLOBAL_VALUE	500
+GLOBAL_VALUE	1000
 GLOBAL_VALUE_ORIGIN	COMPILE-TIME
-DEFAULT_VALUE	500
+DEFAULT_VALUE	1000
 VARIABLE_SCOPE	GLOBAL
 VARIABLE_TYPE	INT UNSIGNED
 VARIABLE_COMMENT	Maximum allowed number of worker threads in the thread pool

mysql-test/suite/sys_vars/r/thread_pool_max_threads_basic.result

 SET @start_global_value = @@global.thread_pool_max_threads;
 select @@global.thread_pool_max_threads;
 @@global.thread_pool_max_threads
-500
+1000
 select @@session.thread_pool_max_threads;
 ERROR HY000: Variable 'thread_pool_max_threads' is a GLOBAL variable
 show global variables like 'thread_pool_max_threads';
 Variable_name	Value
-thread_pool_max_threads	500
+thread_pool_max_threads	1000
 show session variables like 'thread_pool_max_threads';
 Variable_name	Value
-thread_pool_max_threads	500
+thread_pool_max_threads	1000
 select * from information_schema.global_variables where variable_name='thread_pool_max_threads';
 VARIABLE_NAME	VARIABLE_VALUE
-THREAD_POOL_MAX_THREADS	500
+THREAD_POOL_MAX_THREADS	1000
 select * from information_schema.session_variables where variable_name='thread_pool_max_threads';
 VARIABLE_NAME	VARIABLE_VALUE
-THREAD_POOL_MAX_THREADS	500
+THREAD_POOL_MAX_THREADS	1000
 set global thread_pool_max_threads=1;
 select @@global.thread_pool_max_threads;
 @@global.thread_pool_max_threads

sql/sys_vars.cc

@@ -3279,7 +3279,7 @@ static Sys_var_uint Sys_threadpool_max_threads(
   "thread_pool_max_threads",
   "Maximum allowed number of worker threads in the thread pool",
    GLOBAL_VAR(threadpool_max_threads), CMD_LINE(REQUIRED_ARG),
-   VALID_RANGE(1, 65536), DEFAULT(500), BLOCK_SIZE(1),
+   VALID_RANGE(1, 65536), DEFAULT(1000), BLOCK_SIZE(1),
    NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0), 
    ON_UPDATE(fix_tp_max_threads)
 );