MDEV-27923 Deprecate spider_use_handler

Deprecate the plugin variable spider_use_handler and the corresponding
table parameters "uhd" and "use_handler".

Passing a Handler statement to data nodes, without converting it to
SQL sometimes, might improve the performance, while this introduces
some complication to the implementation.

In the first place, only a few people use Handler statements and the
performance gain seems not to be very significant. Further, setting
spider_use_handler > 0 disables the GROUP BY handler. So, we decided
to deprecate the variable.

storage/spider/mysql-test/spider/r/variable_deprecation.result

+#
+# MDEV-27228 Deprecate Spider plugin variables that result in excessive tweak
+#
+for master_1
+for child2
+child2_1
+child2_2
+child2_3
+for child3
+child3_1
+child3_2
+child3_3
+connection master_1;
+CREATE DATABASE auto_test_local;
+USE auto_test_local;
+# MDEV-27923 Deprecate spider_use_handler
+SET spider_use_handler= 3;
+Warnings:
+Warning	1287	'@@spider_use_handler' is deprecated and will be removed in a future release
+SHOW VARIABLES LIKE "spider_use_handler";
+Variable_name	Value
+spider_use_handler	3
+CREATE TABLE tbl_a (a INT) ENGINE=Spider COMMENT='uhd "3"';
+Warnings:
+Warning	1287	The table parameter 'uhd' is deprecated and will be removed in a future release
+CREATE TABLE tbl_b (a INT) ENGINE=Spider COMMENT='use_handler "3"';
+Warnings:
+Warning	1287	The table parameter 'use_handler' is deprecated and will be removed in a future release
+DROP DATABASE auto_test_local;
+for master_1
+for child2
+child2_1
+child2_2
+child2_3
+for child3
+child3_1
+child3_2
+child3_3

storage/spider/mysql-test/spider/t/variable_deprecation.test

+--echo #
+--echo # MDEV-27228 Deprecate Spider plugin variables that result in excessive tweak
+--echo #
+
+--disable_query_log
+--disable_result_log
+--source test_init.inc
+--enable_result_log
+--enable_query_log
+
+--connection master_1
+CREATE DATABASE auto_test_local;
+USE auto_test_local;
+
+--echo # MDEV-27923 Deprecate spider_use_handler
+SET spider_use_handler= 3;
+SHOW VARIABLES LIKE "spider_use_handler";
+eval CREATE TABLE tbl_a (a INT) $MASTER_1_ENGINE COMMENT='uhd "3"';
+eval CREATE TABLE tbl_b (a INT) $MASTER_1_ENGINE COMMENT='use_handler "3"';
+
+DROP DATABASE auto_test_local;
+
+--disable_query_log
+--disable_result_log
+--source test_deinit.inc
+--enable_result_log
+--enable_query_log

storage/spider/spd_param.cc

@@ -2680,7 +2680,7 @@ int spider_param_use_hs_write(
  */
 static MYSQL_THDVAR_INT(
   use_handler, /* name */
-  PLUGIN_VAR_RQCMDARG, /* opt */
+  PLUGIN_VAR_RQCMDARG | PLUGIN_VAR_DEPRECATED, /* opt */
   "Use handler for reading", /* comment */
   NULL, /* check */
   NULL, /* update */

storage/spider/spd_table.cc

@@ -2060,6 +2060,16 @@ int st_spider_param_string_parse::print_param_error()
     } \
     break; \
   }
+#define SPIDER_PARAM_DEPRECATED_WARNING(title_name)                           \
+  if (!strncasecmp(tmp_ptr, title_name, title_length) && create_table)        \
+  {                                                                           \
+    THD *thd= current_thd;                                                    \
+    push_warning_printf(thd, Sql_condition::WARN_LEVEL_WARN,                  \
+                        ER_WARN_DEPRECATED_SYNTAX,                            \
+                        "The table parameter '%s' is deprecated and will be " \
+                        "removed in a future release",                        \
+                        title_name);                                          \
+  }
 
 int spider_parse_connect_info(
   SPIDER_SHARE *share,
@@ -2437,6 +2447,7 @@ int spider_parse_connect_info(
           SPIDER_PARAM_LONG_LIST_WITH_MAX("svc", tgt_ssl_vscs, 0, 1);
           SPIDER_PARAM_STR_LIST("tbl", tgt_table_names);
           SPIDER_PARAM_INT_WITH_MAX("tcm", table_count_mode, 0, 3);
+          SPIDER_PARAM_DEPRECATED_WARNING("uhd");
           SPIDER_PARAM_LONG_LIST_WITH_MAX("uhd", use_handlers, 0, 3);
 #if defined(HS_HAS_SQLCOM) && defined(HAVE_HANDLERSOCKET)
           SPIDER_PARAM_LONG_LIST_WITH_MAX(
@@ -2520,6 +2531,7 @@ int spider_parse_connect_info(
           SPIDER_PARAM_INT_WITH_MAX("sts_bg_mode", sts_bg_mode, 0, 2);
 #endif
           SPIDER_PARAM_LONG_LIST_WITH_MAX("link_status", link_statuses, 0, 3);
+          SPIDER_PARAM_DEPRECATED_WARNING("use_handler");
           SPIDER_PARAM_LONG_LIST_WITH_MAX("use_handler", use_handlers, 0, 3);
 #if defined(HS_HAS_SQLCOM) && defined(HAVE_HANDLERSOCKET)
           SPIDER_PARAM_LONG_LIST_WITH_MAX("use_hs_read", use_hs_reads, 0, 1);