Note:
This topic has been translated from a Chinese forum by GPT and might contain errors.
Original topic: 关于br “支持数据冷备份到外部存储” 的一点疑问
Cold backup: The database system needs to be shut down before performing the relevant data backup.
So, does shutting down the TiDB database system mean shutting down all nodes in the cluster or just the TiDB nodes?
If you shut down everything: running the BR backup command will result in an error (cannot connect to PD).
After PD is turned on: the BR log will report an error (cannot connect to TiKV).
After TiKV is turned on, the backup task can run successfully.
So, it seems that the cold backup mentioned in the official documentation refers to shutting down all TiDB nodes? Is this understanding correct? Can shutting down only the TiDB nodes ensure the consistency of the backup data?
It should be “hot standby” here. You can move the post to the feedback section for feedback~
Cold backup refers to copying the database while it is stopped. The term might be incorrect; it should be written as physical backup.
However, if I shut down all TiDB nodes to ensure no data is written during the backup, although the database system is not completely shut down, it is not considered to be running normally, right? In this case, doesn’t it contradict the definition of “hot backup”?
Stopping all TiDB nodes = stopping the database? Or is it considered stopping part of the database? 
Cold backup generally requires downtime, and it is a relatively simple and straightforward file backup.
Is the shutdown mainly to prohibit data writing? For a distributed architecture like TiDB, stopping all TiDB instances would prohibit data writing. In that case, does stopping TiDB equal a shutdown?
So it seems that with this kind of distributed architecture, stopping TiDB does not equal downtime, right? There’s another point I’m not sure if I understand correctly. If the backup takes a long time and there are data writes during this backup process, due to MVCC, the data written during this period will not actually affect the final backup result, right? When BR issues a backup command, there is a parameter called “backupts.” TiKV will only back up the KV values that match the backupts, and the data written during the backup does not match the backupts, so it will not affect the final backup result.
Yes.
This type of backup is called snapshot backup on the official website. If you do not specify backupts, then BR will select the snapshot corresponding to the start time of the backup.
Combining it with log backup can achieve PITR (Point-In-Time Recovery).
From the official 303 course, BR is hot backup, while cold backup of the database specifically refers to stopping the database and then copying the data files.
The consistency of backup data is ensured by MVCC in BR, and the backed-up data is from a specific point in time.
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