concurrently truncating the same partition hangs DDL

[tangenta]

Bug Report

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1. Minimal reproduce step (Required)

Owner TiDB:

create table test.t (a int primary key) partition by range (a) (
  partition p0 values less than (10),
  partition p1 values less than (maxvalue)
);

Non-owner TiDBs run the following SQL concurrently:

alter table test.t truncate partition p0;

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

All the TRUNCATE statements can be executed successfully.

3. What did you see instead (Required)

DDL hangs. ADMIN SHOW DDL:

Err:[table:1735]Unknown partition 'drop?' in table 't', ErrCount:373, SnapshotVersion:0

4. What is your TiDB version? (Required)

master

commit 9abf9d0bb4f69b54a0282a7d9e89e23b91a54422 (upstream/master)
Author: tiancaiamao <tiancaiamao@gmail.com>
Date:   Tue Jul 13 18:33:32 2021 +0800

    *: reduce NewRuntimeStatsColl() object allocation (#26164)

[ti-srebot]

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