backup 过程中允许 GC

[BusyJay]

Error 报告

This repository is ONLY used to solve problems related to DOCS-CN.
For other issues (TiDB, TiKV, etc), please move to other repositories.

Please answer the following questions before submitting your issue. Thanks!

1. What is the document directory for the problem?

https://github.com/pingcap/docs-cn/blob/master/br/backup-and-restore-tool.md#%E5%A2%9E%E9%87%8F%E5%A4%87%E4%BB%BD

2. How would you like to improve it?

文中说

增量备份开始时间与 lastbackupts 之间不能有 GC

但是只要 GC lifetime > 增量备份开始时间 - lastbacupts，即可进行 GC。

[YuJuncen]

OK, 改成 “GC safepoint 必须在 lastbackupts 之前” 如何？(#3656 )

[BusyJay]

LGTM