titan-configuration: remove the unrecommended steps of updating TiKV configuration (#21217) #21223
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@qiancai This PR has conflicts, I have hold it. |
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Summary of Changes
Hello @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 primarily updates the documentation related to the TiKV Titan storage engine, focusing on the procedure for disabling Titan and the behavior of its associated configuration parameters. The changes aim to provide clearer, safer, and more performant guidance for users, particularly by removing unrecommended steps and adding critical warnings about potential TiKV crashes when disabling Titan in older TiDB versions.
Highlights
- Titan Disabling Procedure Update: I've updated the documentation for disabling the Titan storage engine in TiKV. The revised guidance clarifies that modifying the
rocksdb.titan.enabledconfiguration item tofalseis not recommended for TiDB versions earlier than v8.5.0, as it might lead to TiKV crashes. The documentation now emphasizes that Step 1 (updating configuration and restarting TiKV) is sufficient to disable Titan, and Step 2 (data compaction) can be skipped due to its potential impact on online traffic performance. - TiKV Configuration File Updates: The
tikv-configuration-file.mdhas been updated to reflect changes in therocksdb.titan.enabledconfiguration item. Its default value is nowtruefor TiDB v7.6.0 and later versions. A warning has been added to this section, mirroring the one in the Titan configuration guide, advising against setting this item tofalsefor TiDB versions prior to v8.5.0 to prevent crashes. Additional notes clarify the implications of this default change and how existing clusters are handled during upgrades. - Removal of Unrecommended Steps: The previous 'Step 4' in the Titan disabling procedure, which involved explicitly updating the configuration to disable Titan after compaction, has been removed. This aligns with the new recommendation that Step 1 is generally sufficient and that direct modification of
rocksdb.titan.enabledtofalseshould be approached with caution for older versions.
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Code Review
This PR updates the documentation on how to disable Titan, removing a previously recommended but now discouraged step. The changes are logically correct and improve the technical accuracy of the documentation. However, there are several merge conflict markers (<<<<<<<, =======, >>>>>>>) in both modified files. These are critical issues that must be resolved. Suggestions to fix them have been provided, along with minor rephrasing suggestions to improve clarity and align with the documentation style guide.
| <<<<<<< HEAD | ||
| To disable Titan, perform the following steps: | ||
| ======= | ||
| To disable Titan for all existing and future data, you can take the following steps. Note that you can skip Step 2 because it greatly affects online traffic performance. In fact even without Step 2, the data compaction consumes extra I/O and CPU resources when it moves data from Titan to RocksDB, and performance will degrade (sometimes as much as 50%) when TiKV I/O or CPU resources are limited. | ||
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| > **Warning:** | ||
| > | ||
| > When disabling Titan for TiDB versions earlier than v8.5.0, it is not recommended to modify the TiKV configuration item [`rocksdb.titan.enabled`](/tikv-configuration-file.md#enabled) to `false`, as this might cause TiKV to crash. Following Step 1 is sufficient to disable Titan. | ||
| >>>>>>> 445dea0c18 (titan-configuration: remove the unrecommended steps of updating TiKV configuration (#21217)) |
There was a problem hiding this comment.
It appears there are merge conflict markers in this section that need to be removed. The suggestion below resolves the conflict markers and improves the text.12
Style Guide References
| <<<<<<< HEAD | |
| To disable Titan, perform the following steps: | |
| ======= | |
| To disable Titan for all existing and future data, you can take the following steps. Note that you can skip Step 2 because it greatly affects online traffic performance. In fact even without Step 2, the data compaction consumes extra I/O and CPU resources when it moves data from Titan to RocksDB, and performance will degrade (sometimes as much as 50%) when TiKV I/O or CPU resources are limited. | |
| > **Warning:** | |
| > | |
| > When disabling Titan for TiDB versions earlier than v8.5.0, it is not recommended to modify the TiKV configuration item [`rocksdb.titan.enabled`](/tikv-configuration-file.md#enabled) to `false`, as this might cause TiKV to crash. Following Step 1 is sufficient to disable Titan. | |
| >>>>>>> 445dea0c18 (titan-configuration: remove the unrecommended steps of updating TiKV configuration (#21217)) | |
| To disable Titan for all existing and future data, you can take the following steps. Note that you can skip Step 2, as it can significantly affect online traffic performance. Even without Step 2, data compaction consumes extra I/O and CPU resources when moving data from Titan to RocksDB. This process can degrade performance by as much as 50% when TiKV I/O or CPU resources are limited. | |
| > **Warning:** | |
| > | |
| > When disabling Titan for TiDB versions earlier than v8.5.0, it is not recommended to modify the TiKV configuration item [`rocksdb.titan.enabled`](/tikv-configuration-file.md#enabled) to `false`, as this might cause TiKV to crash. Following Step 1 is sufficient to disable Titan. |
Footnotes
| <<<<<<< HEAD | ||
| 4. Update the configuration of these TiKV nodes to disable Titan. | ||
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| ```toml |
There was a problem hiding this comment.
This section also contains merge conflict markers that must be removed. The goal is to remove the now-obsolete Step 4, and the suggestion will clean up the markers to achieve that.
tikv-configuration-file.md
Outdated
| <<<<<<< HEAD | ||
| + Enables or disables Titan | ||
| + Default value: `false` | ||
| ======= | ||
| > **Warning** | ||
| > | ||
| > When disabling Titan for TiDB versions earlier than v8.5.0, it is not recommended to modify this configuration item to `false`, as this might cause TiKV to crash. To disable Titan, refer to the steps in [Disable Titan](/storage-engine/titan-configuration.md#disable-titan). | ||
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| > **Note:** | ||
| > | ||
| > - To enhance the performance of wide table and JSON data writing and point query, starting from TiDB v7.6.0, the default value changes from `false` to `true`, which means that Titan is enabled by default. | ||
| > - Existing clusters upgraded to v7.6.0 or later versions retain the original configuration, which means that if Titan is not explicitly enabled, it still uses RocksDB. | ||
| > - If the cluster has enabled Titan before upgrading to TiDB v7.6.0 or later versions, Titan will be retained after the upgrade, and the [`min-blob-size`](/tikv-configuration-file.md#min-blob-size) configuration before the upgrade will be retained. If you do not explicitly configure the value before the upgrade, the default value of the previous version `1KiB` will be retained to ensure the stability of the cluster configuration after the upgrade. | ||
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| + Enables or disables Titan. | ||
| + Default value: `true` | ||
| >>>>>>> 445dea0c18 (titan-configuration: remove the unrecommended steps of updating TiKV configuration (#21217)) |
There was a problem hiding this comment.
This section has merge conflict markers that must be resolved. The notes have been rephrased for better clarity and to align with the style guide's preference for using the second person ('you').123
Style Guide References
| <<<<<<< HEAD | |
| + Enables or disables Titan | |
| + Default value: `false` | |
| ======= | |
| > **Warning** | |
| > | |
| > When disabling Titan for TiDB versions earlier than v8.5.0, it is not recommended to modify this configuration item to `false`, as this might cause TiKV to crash. To disable Titan, refer to the steps in [Disable Titan](/storage-engine/titan-configuration.md#disable-titan). | |
| > **Note:** | |
| > | |
| > - To enhance the performance of wide table and JSON data writing and point query, starting from TiDB v7.6.0, the default value changes from `false` to `true`, which means that Titan is enabled by default. | |
| > - Existing clusters upgraded to v7.6.0 or later versions retain the original configuration, which means that if Titan is not explicitly enabled, it still uses RocksDB. | |
| > - If the cluster has enabled Titan before upgrading to TiDB v7.6.0 or later versions, Titan will be retained after the upgrade, and the [`min-blob-size`](/tikv-configuration-file.md#min-blob-size) configuration before the upgrade will be retained. If you do not explicitly configure the value before the upgrade, the default value of the previous version `1KiB` will be retained to ensure the stability of the cluster configuration after the upgrade. | |
| + Enables or disables Titan. | |
| + Default value: `true` | |
| >>>>>>> 445dea0c18 (titan-configuration: remove the unrecommended steps of updating TiKV configuration (#21217)) | |
| > **Warning** | |
| > | |
| > When disabling Titan for TiDB versions earlier than v8.5.0, do not set this configuration item to `false`, as this might cause TiKV to crash. To disable Titan, follow the steps in [Disable Titan](/storage-engine/titan-configuration.md#disable-titan). | |
| > **Note:** | |
| > | |
| > - To enhance performance for wide tables, JSON data writes, and point queries, the default value of this item changes from `false` to `true` starting from TiDB v7.6.0. This means Titan is enabled by default in new clusters. | |
| > - When you upgrade an existing cluster to v7.6.0 or later, its original configuration is retained. If Titan was not explicitly enabled before the upgrade, it remains disabled. | |
| > - If you enabled Titan before upgrading to v7.6.0 or later, it remains enabled after the upgrade, and your pre-upgrade [`min-blob-size`](/tikv-configuration-file.md#min-blob-size) configuration is retained. If you did not explicitly configure this value, it retains the default value from the previous version (`1KiB`) to ensure cluster stability. | |
| + Enables or disables Titan. | |
| + Default value: `true` |
Footnotes
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[APPROVALNOTIFIER] This PR is NOT APPROVED This pull-request has been approved by: The full list of commands accepted by this bot can be found here.
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This is an automated cherry-pick of #21217
First-time contributors' checklist
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This PR updates release-8.1 docs according to pingcap/docs-cn#20304.
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