Query infoschema tables in a large cluster may encounter OOM issue

[tangenta]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

Prepare 1M tables.

select count(1) from information_schema.tables;

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

Return the result or report the error like "Your query has been cancelled due to exceeding the allowed memory limit for a single SQL query. Please try narrowing your query scope or increase the tidb_mem_quota_query limit and try again".

3. What did you see instead (Required)

TiDB OOM and panic.

4. What is your TiDB version? (Required)

1f74ac3

[tangenta]

#51455 fixed a similar issue, but as #51455 (comment) said, the memory has been allocated already. We should provide fine-grained memory control.