v5.0.1 - tidb_enable_async_commit and tidb_enable_1pc cannot be displayed

[glkappe]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

2. What did you expect to see? (Required)

tidb_enable_async_commit and tidb_enable_1pc can be displayed through show variables
like

3. What did you see instead (Required)

4. What is your TiDB version? (Required)

`mysql> \s

mysql Ver 14.14 Distrib 5.6.48-88.0, for Linux (x86_64) using 6.2

Connection id: 5
Current database:
Current user: root@172.16.4.107
SSL: Not in use
Current pager: stdout
Using outfile: ''
Using delimiter: ;
Server version: 5.7.25-TiDB-v5.0.1 TiDB Server (Apache License 2.0) Community Edition, MySQL 5.7 compatible
Protocol version: 10
Connection: 172.16.4.107 via TCP/IP
Server characterset: utf8mb4
Db characterset: utf8mb4
Client characterset: utf8
Conn. characterset: utf8
TCP port: 24000
Uptime: 0 sec

Threads: 0 Questions: 0 Slow queries: 0 Opens: 0 Flush tables: 0 Open tables: 0 Queries per second avg: 0.000

`

[glkappe]

How should I understand this phenomenon！

[morgo]

@glkappe This is intentional, you can se a list of the variables that are hidden here:

tidb/sessionctx/variable/tidb_vars.go

Lines 699 to 713 in 1145e34

	// FeatureSwitchVariables is used to filter result of show variables, these switches should be turn blind to users.
	var FeatureSwitchVariables = []string{
	TiDBEnableChangeColumnType,
	TiDBEnablePointGetCache,
	TiDBEnableAlterPlacement,
	TiDBEnableChangeMultiSchema,
	TiDBEnableAsyncCommit,
	TiDBEnable1PC,
	TiDBGuaranteeLinearizability,
	TiDBTrackAggregateMemoryUsage,
	TiDBAnalyzeVersion,
	TiDBPartitionPruneMode,
	TiDBEnableIndexMergeJoin,
	TiDBEnableExtendedStats,
	}

I am not a fan of it personally. In MySQL all variables always show up in the SHOW VARIABLES list.

[youjiali1995]

tidb_enable_async_commit and tidb_enable_1pc are hidden because they are switches for temporary use. For example, if there are some bugs, we may want to turn off them. And during the rolling upgrade, we can't turn them on because they are not compatible with the old version TiDB and use these variables to turn them on after the upgrade. Normally, these features should be on at all times and we don't want users to use them.

[jebter]

The issue has not been updated for too long, so I will close it. If there are any updates, you can reopen it.