blocking sync load take too much time.

[hawkingrei]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

In order to reproduce the problem easily locally, it is recommended to reduce the configuration file parameter stats-load-queue-size and the system variable tidb_stats_load_sync_wait. It is easier to reproduce the problem if you adjust them to 10 and 1 respectively.
You only need to trigger a large number of fast stats sync load tasks to trigger this problem. I have 2,000 tables locally, each with 20 columns and 20 indexes. Using a script to quickly access all columns of all tables can trigger the problem. The SQL example is as follows.

SELECT * FROM %s WHERE c1 = 1 AND c2 = 2 AND c3 = 3 AND c4 = 4 AND c5 = 5 AND c6 = 6 AND c7 = 7 AND c8 = 8 AND c9 = 9 AND c10 = 10 AND c11 = 1 AND c12 = 2 AND c13 = 3 AND c14 = 4 AND c15 = 5 AND c16 = 6 AND c17 = 7 AND c18 = 8 AND c19 = 9 AND c20 = 10

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

no any time

3. What did you see instead (Required)

4. What is your TiDB version? (Required)

v8.1.0