log backup lag occasionally more than 5 minutes after resume log backup

[Lily2025]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

1、enable IME
2、run muti mvcc workload
3、full backup
4、minio is full during full backup
5、log backup pause due to minio full

6、clean up some space of minio
7、resume log backup task
8、log backup became normal

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

after resume log backup，the lag should be less than 5mins

3. What did you see instead (Required)

log backup lag occasionally more than 5 minutes after resume log backup
and after rolling update tikv，the lag returns to be less than 3 minutes

4. What is your TiDB version? (Required)

./tidb-server -V
Release Version: v8.5.0
Edition: Community
Git Commit Hash: d13e52e
Git Branch: HEAD
UTC Build Time: 2024-12-18 02:26:06
GoVersion: go1.23.3
Race Enabled: false
Check Table Before Drop: false
Store: unistore
2025-01-06T05:48:54.781+0800

[Lily2025]

/severity major
/assign YuJuncen

[YuJuncen]

This is because the checkpoint subscription was disabled after a context canceled error hence TiDB rolls back to poll mode which isn't pretty effective and then the lag increases.

[YuJuncen]

We may keep trying to subscribe when encountering such a failure.