changing @@tidb_schema_cache_size to 0, TableByName miss rate 100%

[tiancaiamao]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

Run some workload like sysbench point get.

First, the @@tidb_schema_cache_size = 512M, the default value.
Change it to 0, check the schema cache hit rate.

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

Hit rate near 100% or no data (infoschema v2 not used)

3. What did you see instead (Required)

Run sysbench_point_get with @@tidb_schema_cache_size = 512M
Set @@tidb_schema_cache_size = 0
Run sysbench_point_get again, the hit rate is nearly 0.

4. What is your TiDB version? (Required)

master e6b4d95

[tiancaiamao]

The user will seldom or never change the value of @@tidb_schema_cache_size, so this is not a big problem.

[jebter]

Releted to issue: #50959