Different tidb node in the same cluster get the different table ID for the same table in `metrics_schema`

[lcwangchao]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

Setup a cluster with 2 tidb nodes.

Run the SQL below in each node:

select tidb_table_id, table_name from information_schema.tables where table_schema='metrics_schema' and table_name='tidb_ddl_total_time' limit 1;

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

The query returns the same result in different TiDB nodes.

3. What did you see instead (Required)

The results are not the same.

In one node

> select tidb_table_id, table_name from information_schema.tables where table_schema='metrics_schema' and table_name='tidb_ddl_total_time' limit 1;
+---------------------+---------------------+
| tidb_table_id       | table_name          |
+---------------------+---------------------+
| 4611686018427408458 | tidb_ddl_total_time |
+---------------------+---------------------+

In another node

> select tidb_table_id, table_name from information_schema.tables where table_schema='metrics_schema' and table_name='tidb_ddl_total_time' limit 1;
+---------------------+---------------------+
| tidb_table_id       | table_name          |
+---------------------+---------------------+
| 4611686018427408007 | tidb_ddl_total_time |
+---------------------+---------------------+
1 row in set
Time: 0.010s

4. What is your TiDB version? (Required)

[lcwangchao]

The meta of tables in metrics_schema is generated in memory by iterating MetricTableMap

tidb/pkg/infoschema/metrics_schema.go

Lines 44 to 56 in 4275195

	tableID := dbID + 1
	metricTables := make([]*model.TableInfo, 0, len(MetricTableMap))
	for name, def := range MetricTableMap {
	cols := def.genColumnInfos()
	tableInfo := buildTableMeta(name, cols)
	tableInfo.ID = tableID
	tableInfo.Comment = def.Comment
	tableInfo.DBID = dbID
	tableID++
	metricTables = append(metricTables, tableInfo)
	tableInfo.MaxColumnID = int64(len(tableInfo.Columns))
	tableInfo.MaxIndexID = int64(len(tableInfo.Indices))
	}

However, MetricTableMap is an object of type map that does not guarantee the order when iterating.

tidb/pkg/infoschema/metric_table_def.go

Line 19 in 4275195

var MetricTableMap = map[string]MetricTableDef{