BR support for placement rules

[morgo]

For BR, when creating a full backup placement rules (all placement policies, not just those in use) will be dumped. Upon a full restore of a backup, they will be restored.

On a partial restore (i.e. one table) they will not be restored, since the behavior around restoring the policy first is unclear.

[lcwangchao]

Details of the specification:

• Backup TiDB placement Policies

  • When backing up the entire cluster (using br backup full), br will back up the tidb placement policies;
  • Otherwise, While backing up the specified database/table (using br backup db/table or table filter), placement policies are not backed up. Placement options in table/database will not be backed up too.

• Restore TiDB placement Policies

  • If backup data contains placement policies data.
    • BR supports all restore policies when using br restore full;
    • While using br restore db/table or table filter, The policies associated with the restored table will be restored;
    • If the placement policy already exists in cluster, br restore just ignores the placement policy in backup data;
      if backup data doesn’t contain placement policies data, br restore will ignore the policy options in the create table statement automatically if it has these options.

If the user does not want to restore the placement policies, or ignore the wrong policies, or restore the data to an earlier version of TiDB (unsupported placement policy), BR provides an ignore option --with-tidb-placement-mode=strict/ignore, which corresponds to the TiDB system variable TIDB_PLACEMENT_MODE:

• STRICT (default): br tries to restore the placement policies if the backup data contains them. BR restores all placement policies for br restore full, and only associated policies for br restore db/table and table filter. If the create table statement cannot be applied because of missing the required object(pollicy, label...), an error is reported by br restore.
• IGNORE: BR ignores all placement policies and the options in the create table statement.

The option only can be used in br restore, it doesn't work for br backup.

[3pointer]

To implement this. we need to do following things.

• Add CreatePlacementPolicyWithInfo to interface ddl.DDL to support br restore #32951
• Add a policyInfos field in BackupMeta
• Write policyInfos to BackupMeta before BackupSchemas when we are in full backup.

  tidb/br/pkg/task/backup.go

  Line 454 in b9bd5a7

  err = schemas.BackupSchemas(

• Restore all policyInfos before create tables during full restoration through createPolicysWithInfos API.
• Restore related policyInfos when create table during table restoration through createPolicysWithInfo API.

[lcwangchao]

@3pointer I think getPolicyInfos , createPolicysWithInfo , createPolicyWithInfo will be added to the ddl.DDL interface ? For getPolicyInfos , the package meta also provides a method meta.ListPolicies , can you use it instead

[3pointer]

meta.ListPolicies is fine. we can use it.

[lcwangchao]

After discussion. We can only provide createPolicysWithInfo