MDEV-24536 innodb_idle_flush_pct has no effect

The parameter innodb_idle_flush_pct that was introduced in
MariaDB Server 10.1.2 by MDEV-6932 has no effect ever since
the InnoDB changes from MySQL 5.7.9 were applied in
commit 2e814d47.

Let us declare the parameter as deprecated and having no effect.

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

@@ -24,6 +24,8 @@ select * from information_schema.session_variables where variable_name='innodb_i
 VARIABLE_NAME	VARIABLE_VALUE
 INNODB_IDLE_FLUSH_PCT	100
 set global innodb_idle_flush_pct=10;
+Warnings:
+Warning	131	innodb_idle_flush_pct is DEPRECATED and has no effect.
 select @@global.innodb_idle_flush_pct;
 @@global.innodb_idle_flush_pct
 10
@@ -44,6 +46,7 @@ ERROR 42000: Incorrect argument type to variable 'innodb_idle_flush_pct'
 set global innodb_idle_flush_pct=-7;
 Warnings:
 Warning	1292	Truncated incorrect innodb_idle_flush_pct value: '-7'
+Warning	131	innodb_idle_flush_pct is DEPRECATED and has no effect.
 select @@global.innodb_idle_flush_pct;
 @@global.innodb_idle_flush_pct
 0
@@ -53,6 +56,7 @@ INNODB_IDLE_FLUSH_PCT	0
 set global innodb_idle_flush_pct=106;
 Warnings:
 Warning	1292	Truncated incorrect innodb_idle_flush_pct value: '106'
+Warning	131	innodb_idle_flush_pct is DEPRECATED and has no effect.
 select @@global.innodb_idle_flush_pct;
 @@global.innodb_idle_flush_pct
 100
@@ -60,18 +64,26 @@ select * from information_schema.global_variables where variable_name='innodb_id
 VARIABLE_NAME	VARIABLE_VALUE
 INNODB_IDLE_FLUSH_PCT	100
 set global innodb_idle_flush_pct=0;
+Warnings:
+Warning	131	innodb_idle_flush_pct is DEPRECATED and has no effect.
 select @@global.innodb_idle_flush_pct;
 @@global.innodb_idle_flush_pct
 0
 set global innodb_idle_flush_pct=100;
+Warnings:
+Warning	131	innodb_idle_flush_pct is DEPRECATED and has no effect.
 select @@global.innodb_idle_flush_pct;
 @@global.innodb_idle_flush_pct
 100
 set global innodb_idle_flush_pct=DEFAULT;
+Warnings:
+Warning	131	innodb_idle_flush_pct is DEPRECATED and has no effect.
 select @@global.innodb_idle_flush_pct;
 @@global.innodb_idle_flush_pct
 100
 SET @@global.innodb_idle_flush_pct = @start_global_value;
+Warnings:
+Warning	131	innodb_idle_flush_pct is DEPRECATED and has no effect.
 SELECT @@global.innodb_idle_flush_pct;
 @@global.innodb_idle_flush_pct
 100

mysql-test/suite/sys_vars/r/sysvars_innodb,32bit.rdiff

@@ -331,7 +331,7 @@
  VARIABLE_SCOPE	GLOBAL
 -VARIABLE_TYPE	BIGINT UNSIGNED
 +VARIABLE_TYPE	INT UNSIGNED
- VARIABLE_COMMENT	Up to what percentage of dirty pages should be flushed when innodb finds it has spare resources to do so.
+ VARIABLE_COMMENT	DEPRECATED. This setting has no effect.
  NUMERIC_MIN_VALUE	0
  NUMERIC_MAX_VALUE	100
 @@ -1306,22 +1306,22 @@

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

@@ -1283,7 +1283,7 @@ SESSION_VALUE	NULL
 DEFAULT_VALUE	100
 VARIABLE_SCOPE	GLOBAL
 VARIABLE_TYPE	BIGINT UNSIGNED
-VARIABLE_COMMENT	Up to what percentage of dirty pages should be flushed when innodb finds it has spare resources to do so.
+VARIABLE_COMMENT	DEPRECATED. This setting has no effect.
 NUMERIC_MIN_VALUE	0
 NUMERIC_MAX_VALUE	100
 NUMERIC_BLOCK_SIZE	0

storage/innobase/handler/ha_innodb.cc

@@ -4,7 +4,7 @@ Copyright (c) 2000, 2020, Oracle and/or its affiliates. All Rights Reserved.
 Copyright (c) 2008, 2009 Google Inc.
 Copyright (c) 2009, Percona Inc.
 Copyright (c) 2012, Facebook Inc.
-Copyright (c) 2013, 2020, MariaDB Corporation.
+Copyright (c) 2013, 2021, MariaDB Corporation.
 
 Portions of this file contain modifications contributed and copyrighted by
 Google, Inc. Those modifications are gratefully acknowledged and are described
@@ -3611,7 +3611,12 @@ static const char*	deprecated_mtflush_threads
 	" and the parameter will be removed in MariaDB 10.3."
 	" Use innodb-page-cleaners instead. ";
 
+/** Deprecation message about innodb_idle_flush_pct */
+static const char*	deprecated_idle_flush_pct
+	= "innodb_idle_flush_pct is DEPRECATED and has no effect.";
+
 static my_bool innodb_instrument_semaphores;
+static ulong innodb_idle_flush_pct;
 
 /** If applicable, emit a message that log checksums cannot be disabled.
 @param[in,out]	thd	client session, or NULL if at startup
@@ -4232,6 +4237,10 @@ innobase_init(
 			" It will be removed in MariaDB 10.3.";
 	}
 
+	if (innodb_idle_flush_pct != 100) {
+		ib::warn() << deprecated_idle_flush_pct;
+	}
+
 	srv_use_atomic_writes
 		= innobase_use_atomic_writes && my_may_have_atomic_write;
         if (srv_use_atomic_writes && !srv_file_per_table)
@@ -19845,6 +19854,14 @@ innodb_instrument_semaphores_update(
 		     HA_ERR_WRONG_COMMAND, deprecated_instrument_semaphores);
 }
 
+static void innodb_idle_flush_pct_update(THD *thd, st_mysql_sys_var *var,
+                                         void*, const void *save)
+{
+  innodb_idle_flush_pct = *static_cast<const ulong*>(save);
+  push_warning(thd, Sql_condition::WARN_LEVEL_WARN,
+               HA_ERR_WRONG_COMMAND, deprecated_idle_flush_pct);
+}
+
 /* plugin options */
 
 static MYSQL_SYSVAR_ENUM(checksum_algorithm, srv_checksum_algorithm,
@@ -19928,12 +19945,10 @@ static MYSQL_SYSVAR_ULONG(io_capacity_max, srv_max_io_capacity,
   SRV_MAX_IO_CAPACITY_DUMMY_DEFAULT, 100,
   SRV_MAX_IO_CAPACITY_LIMIT, 0);
 
-static MYSQL_SYSVAR_ULONG(idle_flush_pct,
-  srv_idle_flush_pct,
+static MYSQL_SYSVAR_ULONG(idle_flush_pct, innodb_idle_flush_pct,
   PLUGIN_VAR_RQCMDARG,
-  "Up to what percentage of dirty pages should be flushed when innodb "
-  "finds it has spare resources to do so.",
-  NULL, NULL, 100, 0, 100, 0);
+  "DEPRECATED. This setting has no effect.",
+  NULL, innodb_idle_flush_pct_update, 100, 0, 100, 0);
 
 #ifdef UNIV_DEBUG
 static MYSQL_SYSVAR_BOOL(background_drop_list_empty,

storage/innobase/include/srv0srv.h

@@ -3,7 +3,7 @@
 Copyright (c) 1995, 2017, Oracle and/or its affiliates. All rights reserved.
 Copyright (c) 2008, 2009, Google Inc.
 Copyright (c) 2009, Percona Inc.
-Copyright (c) 2013, 2018, MariaDB Corporation.
+Copyright (c) 2013, 2021, MariaDB Corporation.
 
 Portions of this file contain modifications contributed and copyrighted by
 Google, Inc. Those modifications are gratefully acknowledged and are described
@@ -435,8 +435,6 @@ extern double	srv_defragment_fill_factor;
 extern uint	srv_defragment_frequency;
 extern ulonglong	srv_defragment_interval;
 
-extern ulong	srv_idle_flush_pct;
-
 extern uint	srv_change_buffer_max_size;
 
 /* Number of IO operations per second the server can do */

storage/innobase/srv/srv0srv.cc

@@ -3,7 +3,7 @@
 Copyright (c) 1995, 2017, Oracle and/or its affiliates. All Rights Reserved.
 Copyright (c) 2008, 2009 Google Inc.
 Copyright (c) 2009, Percona Inc.
-Copyright (c) 2013, 2020, MariaDB Corporation.
+Copyright (c) 2013, 2021, MariaDB Corporation.
 
 Portions of this file contain modifications contributed and copyrighted by
 Google, Inc. Those modifications are gratefully acknowledged and are described
@@ -272,9 +272,6 @@ ulong	srv_buf_pool_dump_pct;
 /** Lock table size in bytes */
 ulint	srv_lock_table_size	= ULINT_MAX;
 
-/** innodb_idle_flush_pct */
-ulong	srv_idle_flush_pct;
-
 /** copy of innodb_read_io_threads */
 ulint	srv_n_read_io_threads;
 /** copy of innodb_write_io_threads */