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restore: update the definition of the parameter --load-stats and the usage of pitr id map (#21078) #22200

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74 changes: 74 additions & 0 deletions br/br-checkpoint-restore.md
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Expand Up @@ -85,4 +85,78 @@ During the initial restore, `br` first enters the snapshot restore phase. This p

When entering the log restore phase during the initial restore, `br` creates a `__TiDB_BR_Temporary_Log_Restore_Checkpoint` database in the target cluster. This database records checkpoint data, the upstream cluster ID, and the restore time range (`start-ts` and `restored-ts`). If restore fails during this phase, you need to specify the same `start-ts` and `restored-ts` as recorded in the checkpoint database when retrying. Otherwise, `br` will report an error and prompt that the current specified restore time range or upstream cluster ID is different from the checkpoint record. If the restore cluster has been cleaned, you can manually delete the `__TiDB_BR_Temporary_Log_Restore_Checkpoint` database and retry with a different backup.

<<<<<<< HEAD
Before entering the log restore phase during the initial restore, `br` constructs a mapping of upstream and downstream cluster database and table IDs at the `restored-ts` time point. This mapping is persisted in the system table `mysql.tidb_pitr_id_map` to prevent duplicate allocation of database and table IDs. Deleting data from `mysql.tidb_pitr_id_map` might lead to inconsistent PITR restore data.
=======
Note that before entering the log restore phase during the initial restore, `br` constructs a mapping of upstream and downstream cluster database and table IDs at the `restored-ts` time point. This mapping is persisted in the system table `mysql.tidb_pitr_id_map` to prevent duplicate allocation of database and table IDs. **Deleting data from `mysql.tidb_pitr_id_map` arbitrarily might lead to inconsistent PITR restore data.**

> **Note:**
>
> To ensure compatibility with clusters of earlier versions, starting from v9.0.0, if the system table `mysql.tidb_pitr_id_map` does not exist in the restore cluster, the `pitr_id_map` data will be written to the log backup directory. The file name is `pitr_id_maps/pitr_id_map.cluster_id:{downstream-cluster-ID}.restored_ts:{restored-ts}`.

## Implementation details: store checkpoint data in the external storage
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high

The document structure has become confusing with the addition of this section. There are now two sections with similar headings (## Implementation details and ## Implementation details: store checkpoint data in the external storage), both describing implementation details but for different storage methods. This can be confusing for readers.

To improve clarity, I suggest restructuring this part of the document. For example, you could have a single ## Implementation details section with two subsections:

## Implementation details

Starting from v9.0.0, BR can store checkpoint data in two ways: in the downstream cluster (default) or in an external storage (by specifying `--checkpoint-storage`).

### Storing checkpoint data in the downstream cluster

... (content from the existing section at line 70) ...

### Storing checkpoint data in an external storage

... (content from this new section) ...

This would provide a clearer structure for the user to understand the two different methods for storing checkpoint data.


> **Note:**
>
> Starting from v9.0.0, BR stores checkpoint data in the downstream cluster by default. You can specify an external storage for checkpoint data using the `--checkpoint-storage` parameter. For example:
>
> ```shell
> ./br restore full -s "s3://backup-bucket/backup-prefix" --checkpoint-storage "s3://temp-bucket/checkpoints"
> ```

In the external storage, the directory structure of the checkpoint data is as follows:

- Root path `restore-{downstream-cluster-ID}` uses the downstream cluster ID `{downstream-cluster-ID}` to distinguish between different restore clusters.
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low

This sentence is a bit redundant. For better readability, consider rephrasing it.

Suggested change
- Root path `restore-{downstream-cluster-ID}` uses the downstream cluster ID `{downstream-cluster-ID}` to distinguish between different restore clusters.
- The root path is `restore-{downstream-cluster-ID}`, where `{downstream-cluster-ID}` is the downstream cluster ID used to distinguish between different restore clusters.

- Path `restore-{downstream-cluster-ID}/log` stores log file checkpoint data during the log restore phase.
- Path `restore-{downstream-cluster-ID}/sst` stores checkpoint data of the SST files that are not backed up by log backup during the log restore phase.
- Path `restore-{downstream-cluster-ID}/snapshot` stores checkpoint data during the snapshot restore phase.

```
.
`-- restore-{downstream-cluster-ID}
|-- log
| |-- checkpoint.meta
| |-- data
| | |-- {uuid}.cpt
| | |-- {uuid}.cpt
| | `-- {uuid}.cpt
| |-- ingest_index.meta
| `-- progress.meta
|-- snapshot
| |-- checkpoint.meta
| |-- checksum
| | |-- {uuid}.cpt
| | |-- {uuid}.cpt
| | `-- {uuid}.cpt
| `-- data
| |-- {uuid}.cpt
| |-- {uuid}.cpt
| `-- {uuid}.cpt
`-- sst
`-- checkpoint.meta
```

Checkpoint restore operations are divided into two parts: snapshot restore and PITR restore.

### Snapshot restore

During the initial restore, `br` creates a `restore-{downstream-cluster-ID}/snapshot` path in the target cluster. The path records checkpoint data, the upstream cluster ID, and the BackupTS of the backup data.
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medium

The phrase 'in the target cluster' is incorrect here, as this section describes storing data in an external storage. It should be 'in the specified external storage'. Also, the second sentence could be more active.

Suggested change
During the initial restore, `br` creates a `restore-{downstream-cluster-ID}/snapshot` path in the target cluster. The path records checkpoint data, the upstream cluster ID, and the BackupTS of the backup data.
During the initial restore, `br` creates a `restore-{downstream-cluster-ID}/snapshot` path in the specified external storage. In this path, `br` records checkpoint data, the upstream cluster ID, and the BackupTS of the backup data.


If the restore fails, you can retry it using the same command. `br` will automatically read the checkpoint information from the specified external storage path and resume from the last restore point.

If the restore fails and you try to restore backup data with different checkpoint information to the same cluster, `br` reports an error. It indicates that the current upstream cluster ID or BackupTS is different from the checkpoint record. If the restore cluster has been cleaned, you can manually clean up the checkpoint data in the external storage or specify another external storage path to store checkpoint data, and retry with a different backup.

### PITR restore

[PITR (Point-in-time recovery)](/br/br-pitr-guide.md) consists of snapshot restore and log restore phases.

During the initial restore, `br` first enters the snapshot restore phase. BR records the checkpoint data, the upstream cluster ID, BackupTS of the backup data (that is, the start time point `start-ts` of log restore) and the restored time point `restored-ts` of log restore in the `restore-{downstream-cluster-ID}/snapshot` path. If restore fails during this phase, you cannot adjust the `start-ts` and `restored-ts` of log restore when resuming checkpoint restore.
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low

This sentence is quite long and complex, which can make it hard to read. Consider breaking it into smaller sentences for better clarity.

Suggested change
During the initial restore, `br` first enters the snapshot restore phase. BR records the checkpoint data, the upstream cluster ID, BackupTS of the backup data (that is, the start time point `start-ts` of log restore) and the restored time point `restored-ts` of log restore in the `restore-{downstream-cluster-ID}/snapshot` path. If restore fails during this phase, you cannot adjust the `start-ts` and `restored-ts` of log restore when resuming checkpoint restore.
During the initial restore, `br` first enters the snapshot restore phase. In this phase, BR records the checkpoint data, the upstream cluster ID, the BackupTS of the backup data (which is the start time point `start-ts` of the log restore), and the restored time point `restored-ts` of the log restore in the `restore-{downstream-cluster-ID}/snapshot` path. If the restore fails during this phase, you cannot adjust `start-ts` and `restored-ts` when resuming the checkpoint restore.


When entering the log restore phase during the initial restore, `br` creates a `restore-{downstream-cluster-ID}/log` path in the target cluster. This path records checkpoint data, the upstream cluster ID, and the restore time range (`start-ts` and `restored-ts`). If restore fails during this phase, you need to specify the same `start-ts` and `restored-ts` as recorded in the checkpoint database when retrying. Otherwise, `br` will report an error and prompt that the current specified restore time range or upstream cluster ID is different from the checkpoint record. If the restore cluster has been cleaned, you can manually clean up the checkpoint data in the external storage or specify another external storage path to store checkpoint data, and retry with a different backup.
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medium

The phrase 'in the target cluster' is incorrect here, as this section is about storing data in an external storage. It should be 'in the specified external storage'.

Suggested change
When entering the log restore phase during the initial restore, `br` creates a `restore-{downstream-cluster-ID}/log` path in the target cluster. This path records checkpoint data, the upstream cluster ID, and the restore time range (`start-ts` and `restored-ts`). If restore fails during this phase, you need to specify the same `start-ts` and `restored-ts` as recorded in the checkpoint database when retrying. Otherwise, `br` will report an error and prompt that the current specified restore time range or upstream cluster ID is different from the checkpoint record. If the restore cluster has been cleaned, you can manually clean up the checkpoint data in the external storage or specify another external storage path to store checkpoint data, and retry with a different backup.
When entering the log restore phase during the initial restore, `br` creates a `restore-{downstream-cluster-ID}/log` path in the specified external storage. This path records checkpoint data, the upstream cluster ID, and the restore time range (`start-ts` and `restored-ts`).


Note that before entering the log restore phase during the initial restore, `br` constructs a mapping of the database and table IDs in the upstream and downstream clusters at the `restored-ts` time point. This mapping is persisted in the checkpoint storage with the file name `pitr_id_maps/pitr_id_map.cluster_id:{downstream-cluster-ID}.restored_ts:{restored-ts}` to prevent duplicate allocation of database and table IDs. **Deleting files from the directory `pitr_id_maps` arbitrarily might lead to inconsistent PITR restore data.**

> **Note:**
>
> To ensure compatibility with clusters of earlier versions, starting from v9.0.0, if the system table `mysql.tidb_pitr_id_map` does not exist in the restore cluster and the `--checkpoint-storage` parameter is not specified, the `pitr_id_map` data will be written to the log backup directory. The file name is `pitr_id_maps/pitr_id_map.cluster_id:{downstream-cluster-ID}.restored_ts:{restored-ts}`.
>>>>>>> 827df4ff8c (restore: update the definition of the parameter --load-stats and the usage of pitr id map (#21078))
Comment on lines +88 to +162
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critical

These merge conflict markers (<<<<<<< HEAD, =======, >>>>>>>) were left in the file. They need to be removed to ensure the document renders correctly. Please remove the markers and the content between <<<<<<< HEAD and =======.

1 change: 1 addition & 0 deletions br/br-snapshot-guide.md
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Expand Up @@ -129,6 +129,7 @@ tiup br restore full \
- Starting from BR v5.1.0, when you back up snapshots, BR automatically backs up the **system tables** in the `mysql` schema, but does not restore these system tables by default.
- Starting from v6.2.0, BR lets you specify `--with-sys-table` to restore **data in some system tables**.
- Starting from v7.6.0, BR enables `--with-sys-table` by default, which means that BR restores **data in some system tables** by default.
- Starting from v9.0.0, BR lets you specify `--fast-load-sys-tables` to restore system tables physically. This approach uses the `RENAME TABLE` DDL statement to atomically swap the system tables in the `__TiDB_BR_Temporary_mysql` database with the system tables in the `mysql` database. Unlike the logical restoration of system tables using the `REPLACE INTO` SQL statement, physical restoration completely overwrites the existing data in the system tables.

**BR can restore data in the following system tables:**

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29 changes: 29 additions & 0 deletions br/br-snapshot-manual.md
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Expand Up @@ -127,8 +127,21 @@ tiup br restore full \
--storage local:///br_data/ --pd "${PD_IP}:2379" --log-file restore.log
```

> **Note:**
>
> Starting from v9.0.0, when the `--load-stats` parameter is set to `false`, BR no longer writes statistics for the restored tables to the `mysql.stats_meta` table. After the restore is complete, you can manually execute the [`ANALYZE TABLE`](/sql-statements/sql-statement-analyze-table.md) SQL statement to update the relevant statistics.

When the backup and restore feature backs up data, it stores statistics in JSON format within the `backupmeta` file. When restoring data, it loads statistics in JSON format into the cluster. For more information, see [LOAD STATS](/sql-statements/sql-statement-load-stats.md).

Starting from 9.0.0, BR introduces the `--fast-load-sys-tables` parameter, which is enabled by default. When restoring data to a new cluster using the `br` command-line tool, and the IDs of tables and partitions between the upstream and downstream clusters can be reused (otherwise, BR will automatically fall back to logically load statistics), enabling `--fast-load-sys-tables` lets BR to first restore the statistics-related system tables to the temporary system database `__TiDB_BR_Temporary_mysql`, and then atomically swap these tables with the corresponding tables in the `mysql` database using the `RENAME TABLE` statement.
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medium

This sentence is very long and contains a lot of information, making it difficult to parse. For better readability, consider breaking it down into smaller, more focused sentences. Also, there are a few minor formatting and grammar issues. For example, 9.0.0 should be v9.0.0 for consistency, and some terms should be enclosed in backticks.

Suggested change
Starting from 9.0.0, BR introduces the `--fast-load-sys-tables` parameter, which is enabled by default. When restoring data to a new cluster using the `br` command-line tool, and the IDs of tables and partitions between the upstream and downstream clusters can be reused (otherwise, BR will automatically fall back to logically load statistics), enabling `--fast-load-sys-tables` lets BR to first restore the statistics-related system tables to the temporary system database `__TiDB_BR_Temporary_mysql`, and then atomically swap these tables with the corresponding tables in the `mysql` database using the `RENAME TABLE` statement.
Starting from v9.0.0, BR introduces the `--fast-load-sys-tables` parameter, which is enabled by default to enable physical restore of statistics. When you restore data to a new cluster using the `br` command-line tool, if the IDs of tables and partitions can be reused between the upstream and downstream clusters, BR first restores the statistics-related system tables to the temporary system database `__TiDB_BR_Temporary_mysql`. Then, it atomically swaps these tables with the corresponding tables in the `mysql` database using the `RENAME TABLE` statement. If table and partition IDs cannot be reused, BR automatically falls back to logically loading statistics.


The following is an example:

```shell
tiup br restore full \
--storage local:///br_data/ --pd "${PD_IP}:2379" --log-file restore.log --load-stats --fast-load-sys-tables
```

## Encrypt the backup data

BR supports encrypting backup data at the backup side and [at the storage side when backing up to Amazon S3](/br/backup-and-restore-storages.md#amazon-s3-server-side-encryption). You can choose either encryption method as required.
Expand Down Expand Up @@ -179,6 +192,22 @@ During restore, a progress bar is displayed in the terminal as shown below. When
Full Restore <---------/...............................................> 17.12%.
```

Starting from TiDB v9.0.0, BR lets you specify `--fast-load-sys-tables` to restore statistics physically in a new cluster:

```shell
tiup br restore full \
--pd "${PD_IP}:2379" \
--with-sys-table \
--fast-load-sys-tables \
--storage "s3://${backup_collection_addr}/snapshot-${date}?access-key=${access-key}&secret-access-key=${secret-access-key}" \
--ratelimit 128 \
--log-file restorefull.log
```

> **Note:**
>
> Unlike the logical restoration of system tables using the `REPLACE INTO` SQL statement, physical restoration completely overwrites the existing data in the system tables.

## Restore a database or a table

You can use `br` to restore partial data of a specified database or table from backup data. This feature allows you to filter out data that you do not need during the restore.
Expand Down