MDEV-16952 Introduce SET GLOBAL innodb_max_purge_lag_wait

Let us introduce a dummy variable innodb_max_purge_lag_wait
for waiting that the InnoDB history list length is below
the user-specified limit. Specifically,

SET GLOBAL innodb_max_purge_lag_wait=0;

should wait for all history to be purged. This could be useful
when upgrading from an older version to MariaDB 10.3 or later,
to avoid hitting MDEV-15912.

Note: the history cannot be purged if there exist transactions
that may see old versions.

Reviewed by: Vladislav Vaintroub

mysql-test/suite/innodb/include/wait_all_purged.inc

 # Wait for everything to be purged.
 # The user should have set innodb_purge_rseg_truncate_frequency=1.
 
+--disable_query_log
 if (!$wait_all_purged)
 {
-  let $wait_all_purged= 0;
+  SET GLOBAL innodb_max_purge_lag_wait= 0;
 }
-let $remaining_expect= `select concat('InnoDB		',$wait_all_purged)`;
-
-let $wait_counter= 600;
-while ($wait_counter)
+if ($wait_all_purged)
 {
-    --replace_regex /.*History list length ([0-9]+).*/\1/
-    let $remaining= `SHOW ENGINE INNODB STATUS`;
-    if ($remaining == $remaining_expect)
-    {
-        let $wait_counter= 0;
-    }
-    if ($wait_counter)
-    {
-        real_sleep 0.1;
-        dec $wait_counter;
-    }
+  eval SET GLOBAL innodb_max_purge_lag_wait= $wait_all_purged;
 }
+--enable_query_log
+
+--replace_regex /.*History list length ([0-9]+).*/\1/
+let $remaining= `SHOW ENGINE INNODB STATUS`;
 echo $remaining transactions not purged;

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

@@ -1686,6 +1686,18 @@ NUMERIC_BLOCK_SIZE	0
 ENUM_VALUE_LIST	NULL
 READ_ONLY	NO
 COMMAND_LINE_ARGUMENT	REQUIRED
+VARIABLE_NAME	INNODB_MAX_PURGE_LAG_WAIT
+SESSION_VALUE	NULL
+DEFAULT_VALUE	4294967295
+VARIABLE_SCOPE	GLOBAL
+VARIABLE_TYPE	INT UNSIGNED
+VARIABLE_COMMENT	Wait until History list length is below the specified limit
+NUMERIC_MIN_VALUE	0
+NUMERIC_MAX_VALUE	4294967295
+NUMERIC_BLOCK_SIZE	0
+ENUM_VALUE_LIST	NULL
+READ_ONLY	NO
+COMMAND_LINE_ARGUMENT	REQUIRED
 VARIABLE_NAME	INNODB_MAX_UNDO_LOG_SIZE
 SESSION_VALUE	NULL
 DEFAULT_VALUE	10485760

storage/innobase/handler/ha_innodb.cc

@@ -271,6 +271,27 @@ enum default_row_format_enum {
 	DEFAULT_ROW_FORMAT_DYNAMIC = 2,
 };
 
+/** A dummy variable */
+static uint innodb_max_purge_lag_wait;
+
+/** Wait for trx_sys_t::rseg_history_len to be below a limit. */
+static void innodb_max_purge_lag_wait_update(THD *thd, st_mysql_sys_var *,
+                                             void *, const void *limit)
+{
+  const uint l= *static_cast<const uint*>(limit);
+  if (trx_sys->rseg_history_len <= l)
+    return;
+  mysql_mutex_unlock(&LOCK_global_system_variables);
+  while (trx_sys->rseg_history_len > l)
+  {
+    if (thd_kill_level(thd))
+      break;
+    srv_wake_purge_thread_if_not_active();
+    os_thread_sleep(100000);
+  }
+  mysql_mutex_lock(&LOCK_global_system_variables);
+}
+
 static
 void set_my_errno(int err)
 {
@@ -20147,6 +20168,11 @@ static MYSQL_SYSVAR_ULONG(max_purge_lag_delay, srv_max_purge_lag_delay,
    0L,			/* Minimum value */
    10000000UL, 0);	/* Maximum value */
 
+static MYSQL_SYSVAR_UINT(max_purge_lag_wait, innodb_max_purge_lag_wait,
+  PLUGIN_VAR_RQCMDARG,
+  "Wait until History list length is below the specified limit",
+  NULL, innodb_max_purge_lag_wait_update, UINT_MAX, 0, UINT_MAX, 0);
+
 static MYSQL_SYSVAR_BOOL(rollback_on_timeout, innobase_rollback_on_timeout,
   PLUGIN_VAR_OPCMDARG | PLUGIN_VAR_READONLY,
   "Roll back the complete transaction on lock wait timeout, for 4.x compatibility (disabled by default)",
@@ -21195,6 +21221,7 @@ static struct st_mysql_sys_var* innobase_system_variables[]= {
   MYSQL_SYSVAR(flushing_avg_loops),
   MYSQL_SYSVAR(max_purge_lag),
   MYSQL_SYSVAR(max_purge_lag_delay),
+  MYSQL_SYSVAR(max_purge_lag_wait),
   MYSQL_SYSVAR(old_blocks_pct),
   MYSQL_SYSVAR(old_blocks_time),
   MYSQL_SYSVAR(open_files),