restore: update the definition of the parameter --load-stats and the usage of pitr id map (#21078) #22200
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Summary of ChangesHello @ti-chi-bot, I'm Gemini Code Assist1! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed! This pull request updates the documentation for TiDB's Backup & Restore (BR) tool, enhancing clarity around Point-in-Time Recovery (PITR) ID map management and introducing new features for checkpoint data storage and system table restoration. The changes provide users with more detailed guidance on configuring and understanding BR's behavior, particularly for newer versions, and introduce a more efficient method for restoring system tables. Highlights
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Code Review
This pull request updates documentation related to restore operations, specifically for checkpoint restore and snapshot restore. It introduces new features available from v9.0.0, such as storing checkpoint data in external storage and using --fast-load-sys-tables for physical restore of system tables.
My review focuses on improving the clarity and structure of the documentation. I've identified a critical issue where merge conflict markers were left in br/br-checkpoint-restore.md, which will break the document rendering. I've also suggested a significant restructuring of that document to avoid confusion caused by duplicated section headings and to better present the different methods for storing checkpoint data. Additionally, I've provided suggestions to correct inaccuracies (like 'target cluster' instead of 'external storage'), improve sentence structure for better readability, and ensure consistent formatting.
br/br-checkpoint-restore.md
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| 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. | ||
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| 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.** | ||
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| > **Note:** | ||
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| > 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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| > **Note:** | ||
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| > 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. | ||
| - 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. | ||
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| ### Snapshot restore | ||
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| 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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| 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. | ||
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| 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. | ||
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| ### PITR restore | ||
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| [PITR (Point-in-time recovery)](/br/br-pitr-guide.md) consists of snapshot restore and log restore phases. | ||
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| 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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| 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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| 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.** | ||
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| > **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)) |
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This is an automated cherry-pick of #21078
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Note
This PR brings some updates added in #20492. Need to double check whether those changes can be merged into v8.5.
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What is the related PR or file link(s)?
--load-statsand the usage of pitr id map docs-cn#20346Do your changes match any of the following descriptions?