TiDB Log Backup and PITR Guide

A full backup (snapshot backup) contains the full cluster data at a certain point, while TiDB log backup can back up data written by applications to a specified storage in a timely manner. If you want to choose the restore point as required, that is, to perform point-in-time recovery (PITR), you can start log backup and run full backup regularly.

Before you back up or restore data using the br command-line tool (hereinafter referred to as br), you need to install br first.

Back up TiDB cluster

Start log backup

Note

The following examples assume that Amazon S3 access keys and secret keys are used to authorize permissions. If IAM roles are used to authorize permissions, you need to set --send-credentials-to-tikv to false.
If other storage systems or authorization methods are used to authorize permissions, adjust the parameter settings according to Backup Storages.

To start a log backup, run br log start. A cluster can only run one log backup task each time.

tiup br log start --task-name=pitr --pd "${PD_IP}:2379" \
--storage 's3://backup-101/logbackup?access-key=${access-key}&secret-access-key=${secret-access-key}'

After the log backup task starts, it runs in the background of the TiDB cluster until you stop it manually. During this process, the TiDB change logs are regularly backed up to the specified storage in small batches. To query the status of the log backup task, run the following command:

tiup br log status --task-name=pitr --pd "${PD_IP}:2379"

Expected output:

● Total 1 Tasks.
> #1 <
    name: pitr
    status: ● NORMAL
    start: 2022-05-13 11:09:40.7 +0800
      end: 2035-01-01 00:00:00 +0800
    storage: s3://backup-101/log-backup
    speed(est.): 0.00 ops/s
checkpoint[global]: 2022-05-13 11:31:47.2 +0800; gap=4m53s

Run full backup regularly

The snapshot backup can be used as a method of full backup. You can run br backup full to back up the cluster snapshot to the backup storage according to a fixed schedule (for example, every 2 days).

tiup br backup full --pd "${PD_IP}:2379" \
--storage 's3://backup-101/snapshot-${date}?access-key=${access-key}&secret-access-key=${secret-access-key}'

Run PITR

To restore the cluster to any point in time within the backup retention period, you can use br restore point. When you run this command, you need to specify the time point you want to restore, the latest snapshot backup data before the time point, and the log backup data. BR will automatically determine and read data needed for the restore, and then restore these data to the specified cluster in order.

br restore point --pd "${PD_IP}:2379" \
--storage='s3://backup-101/logbackup?access-key=${access-key}&secret-access-key=${secret-access-key}' \
--full-backup-storage='s3://backup-101/snapshot-${date}?access-key=${access-key}&secret-access-key=${secret-access-key}' \
--restored-ts '2022-05-15 18:00:00+0800'

During data restore, you can view the progress through the progress bar in the terminal. The restore is divided into two phases, full restore and log restore (restore meta files and restore KV files). After each phase is completed, br outputs information such as restore time and data size.

Full Restore <--------------------------------------------------------------------------------------------------------------------------------------------------------> 100.00%
*** ["Full Restore success summary"] ****** [total-take=xxx.xxxs] [restore-data-size(after-compressed)=xxx.xxx] [Size=xxxx] [BackupTS={TS}] [total-kv=xxx] [total-kv-size=xxx] [average-speed=xxx]
Restore Meta Files <--------------------------------------------------------------------------------------------------------------------------------------------------> 100.00%
Restore KV Files <----------------------------------------------------------------------------------------------------------------------------------------------------> 100.00%
*** ["restore log success summary"] [total-take=xxx.xx] [restore-from={TS}] [restore-to={TS}] [total-kv-count=xxx] [total-size=xxx]

Clean up outdated data

As described in the Usage Overview of TiDB Backup and Restore:

To perform PITR, you need to restore the full backup before the restore point, and the log backup between the full backup point and the restore point. Therefore, for log backups that exceed the backup retention period, you can use br log truncate to delete the backup before the specified time point. It is recommended to only delete the log backup before the full snapshot.

The following steps describe how to clean up backup data that exceeds the backup retention period:

Get the last full backup outside the backup retention period.
Use the validate command to get the time point corresponding to the backup. Assume that the backup data before 2022/09/01 needs to be cleaned, you should look for the last full backup before this time point and ensure that it will not be cleaned.
```
FULL_BACKUP_TS=`tiup br validate decode --field="end-version" --storage "s3://backup-101/snapshot-${date}?access-key=${access-key}&secret-access-key=${secret-access-key}"| tail -n1`
```

Delete log backup data earlier than the snapshot backup FULL_BACKUP_TS:

tiup br log truncate --until=${FULL_BACKUP_TS} --storage='s3://backup-101/logbackup?access-key=${access-key}&secret-access-key=${secret-access-key}'

Delete snapshot data earlier than the snapshot backup FULL_BACKUP_TS:
```
rm -rf s3://backup-101/snapshot-${date}
```

Performance capabilities of PITR

On each TiKV node, PITR can restore snapshot data (full restore) at a speed of 280 GB/h and log data (including meta files and KV files) at a speed of 30 GB/h.
BR deletes outdated log backup data (tiup br log truncate) at a speed of 600 GB/h.

Note

The preceding specifications are based on test results from the following two testing scenarios. The actual data might be different.

Snapshot data restore speed = Snapshot data size / (duration * the number of TiKV nodes)
Log data restore speed = Restored log data size / (duration * the number of TiKV nodes)

The snapshot data size refers to the logical size of all KVs in a single replica, not the actual amount of restored data. BR restores all replicas according to the number of replicas configured for the cluster. The more replicas there are, the more data can be actually restored. The default replica number for all clusters in the test is 3. To improve the overall restore performance, you can modify the import.num-threads item in the TiKV configuration file and the concurrency option in the BR command.

Testing scenario 1 (on TiDB Cloud) is as follows:

The number of TiKV nodes (8 core, 16 GB memory): 21
TiKV configuration item import.num-threads: 8
BR command option concurrency: 128
The number of Regions: 183,000
New log data created in the cluster: 10 GB/h
Write (INSERT/UPDATE/DELETE) QPS: 10,000

Testing scenario 2 (on TiDB Self-Managed) is as follows:

The number of TiKV nodes (8 core, 64 GB memory): 6
TiKV configuration item import.num-threads: 8
BR command option concurrency: 128
The number of Regions: 50,000
New log data created in the cluster: 10 GB/h
Write (INSERT/UPDATE/DELETE) QPS: 10,000

Monitoring and alert

After log backup tasks are distributed, each TiKV node continuously writes data to external storage. You can view the monitoring data for this process in the TiKV-Details > Backup Log dashboard.

To receive notifications metrics deviate from normal ranges, see Log backup alerts to configure alert rules.