Use BR to Restore Cluster Data

This document describes how to restore cluster data using BR in the following scenarios:

If you are not familiar with Backup & Restore (BR), it is recommended that you read the following documents to fully understand BR usage principles and methods:

Restore TiDB cluster snapshots

BR supports restoring snapshot backup on an empty cluster to restore the target cluster to the latest state when the snapshot is backed up.

Example: Restore the snapshot generated at 2022-01-30 07:42:23 from the 2022-01-30/ directory in the backup-data bucket of Amazon S3 to the target cluster.

br restore full \
    --pd "${PDIP}:2379" \
    --storage "s3://backup-data/2022-01-30/" \
    --ratelimit 128 \
    --log-file restorefull.log

In the preceding command,

  • --ratelimit: The maximum speed for each TiKV to perform a restoration task (unit: MiB/s)
  • --log-file The target file for BR logging

During restoration, a progress bar is displayed in the terminal, as shown below. When the progress bar advances to 100%, the restoration is complete. To ensure data security, BR performs a check on the restored data.

br restore full \
    --pd "${PDIP}:2379" \
    --storage "s3://backup-data/2022-01-30/" \
    --ratelimit 128 \
    --log-file restorefull.log
Full Restore <---------/...............................................> 17.12%.

Restore a database or a table

BR supports restoring partial data of a specified database or table from backup data. This feature allows you to filter out unwanted data and back up only a specific database or table.

Restore a database

To restore a database to the cluster, run the br restore db command. To get help on this command, run the br restore db --help command.

Example: Restore the test database from the db-test/2022-01-30/ directory in the backup-data bucket of Amazon S3 to the target cluster.

br restore db \
    --pd "${PDIP}:2379" \
    --db "test" \
    --ratelimit 128 \
    --storage "s3://backup-data/db-test/2022-01-30/" \
    --log-file restore_db.log

In the preceding command, --db specifies the name of the database to be restored, and other parameters are the same as those in Restore TiDB cluster snapshots.

Note

When you restore the backup data, the database name specified by --db must be the same as the one specified by -- db in the backup command. Otherwise, the restoration fails. This is because the metafile of the backup data ( backupmeta file) records the database name, and you can only restore data to the database with the same name. The recommended method is to restore the backup data to the database with the same name in another cluster.

Restore a table

To restore a single table to the cluster, run the br restore table command. To get help on this command, run the br restore table --help command.

Example: Restore test.usertable from the table-db-usertable/2022-01-30/directory in the backup-data bucket of Amazon S3 to the target cluster.

br restore table \
    --pd "${PDIP}:2379" \
    --db "test" \
    --table "usertable" \
    --ratelimit 128 \
    --storage "s3://backup-data/table-db-usertable/2022-01-30/" \
    --log-file restore_table.log

In the preceding command, --table specifies the name of the table to be restored, and other parameters are the same as those in Restore TiDB cluster snapshots.

Restore multiple tables with table filter

To restore multiple tables with more criteria, run the br restore full command and specify the table filters with --filter or -f.

Example: Restore data matching the db*.tbl* table from the table-filter/2022-01-30/ directory in the backup-data bucket of Amazon S3 to the target cluster.

br restore full \
    --pd "${PDIP}:2379" \
    --filter 'db*.tbl*' \
    --storage "s3://backup-data/table-filter/2022-01-30/"  \
    --log-file restorefull.log

Restore backup data from external storage

BR supports restoring data to Amazon S3, Google Cloud Storage (GCS), Azure Blob Storage, NFS, or other S3-compatible file storage services. For details, see the following documents:

Restore incremental data

Warning

This is still an experimental feature. It is NOT recommended that you use it in the production environment.

Restoring incremental data is similar to restoring full data using BR. When restoring incremental data, make sure that all the data backed up before last backup ts has been restored to the target cluster. Also, because incremental restoration updates ts data, you need to ensure that there are no other writes during the restoration. Otherwise, conflicts might occur.

br restore full \
    --pd "${PDIP}:2379" \
    --storage "s3://backup-data/2022-01-30/incr"  \
    --ratelimit 128 \
    --log-file restorefull.log

Restore encrypted backup data

Warning

This is still an experimental feature. It is NOT recommended that you use it in the production environment.

After encrypting the backup data, you need to pass in the corresponding decryption parameters to restore the data. Ensure that the decryption algorithm and key are correct. If the decryption algorithm or key is incorrect, the data cannot be restored.

br restore full\
    --pd ${PDIP}:2379 \
    --storage "s3://backup-data/2022-01-30/" \
    --crypter.method aes128-ctr \
    --crypter.key 0123456789abcdef0123456789abcdef

Restore tables in the mysql schema

Starting from BR v5.1.0, when you perform a full backup, BR backs up the system tables. Before BR v6.2.0, under default configuration, BR only restores user data, but does not restore data in the system tables. Starting from BR v6.2.0, if the backup data contains system tables, and if you configure --with-sys-table, BR restores data in some system tables.

BR can restore data in the following system tables:

+----------------------------------+
| mysql.columns_priv               |
| mysql.db                         |
| mysql.default_roles              |
| mysql.global_grants              |
| mysql.global_priv                |
| mysql.role_edges                 |
| mysql.tables_priv                |
| mysql.user                       |
+----------------------------------+

BR does not restore the following system tables:

  • Statistics tables (mysql.stat_*)
  • System variable tables (mysql.tidb, mysql.global_variables)
  • Other system tables

When you restore data related to system privileges, note the following:

  • BR does not restore user data with user as cloud_admin and host as '%'. This user is reserved for TiDB Cloud. Do not create a user or role named cloud_admin in your environment, because the user privileges related to cloud_admin cannot be restored correctly.

  • Before BR restores data, it checks whether the system tables in the target cluster are compatible with those in the backup data. "Compatible" means that all the following conditions are met:

    • The target cluster has the same system tables as the backup data.
    • The number of columns in the system privilege table of the target cluster is consistent with that of the backup data. The order of the columns can be different.
    • The columns in the system privilege table of the target cluster are compatible with those in the backup data. If the data type of the column is a type with length (for example, int or char), the length in the target cluster must be >= the length in the backup data. If the data type of the column is an enum type, the enum values in the target cluster must be a superset of the enum values in the backup data.

If the target cluster is not empty or the target cluster is not compatible with the backup data, BR returns the following information. You can remove --with-sys-table to skip restoring system tables.

#######################################################################
# the target cluster is not compatible with the backup data,
# br cannot restore system tables.
# you can remove 'with-sys-table' flag to skip restoring system tables
#######################################################################

To restore a table created by the user in the mysql schema (not system tables), you can explicitly include the table using table filters. The following example shows how to restore the mysql.usertable table when BR performs a normal restoration.

br restore full -f '*.*' -f '!mysql.*' -f 'mysql.usertable' -s $external_storage_url --with-sys-table

In the preceding command,

  • -f '*.*' is used to override the default rules
  • -f '!mysql.*' instructs BR not to restore tables in mysql unless otherwise stated.
  • -f 'mysql.usertable' indicates that mysql.usertable should be restored.

If you only need to restore mysql.usertable, run the following command:

br restore full -f 'mysql.usertable' -s $external_storage_url --with-sys-table

Restoration performance and impact

  • TiDB fully uses TiKV CPU, disk IO, network bandwidth, and other resources when restoring data. Therefore, it is recommended that you restore backup data on an empty cluster to avoid affecting running services.
  • The restoration speed depends much on cluser configuration, deployment, and running services. Generally, the restoration speed can reach 100 MB/s (per TiKV node).
Note

The preceding test conclusions, based on simulation tests in many scenarios and verified in some customer sites, are worthy of reference. However, the restoration speed may vary depending on the scenarios. Therefore, you should always run the test and verify the test results.

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