titan-configuration: remove the unrecommended steps of updating TiKV configuration (#21217) #21224
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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 focuses on enhancing the accuracy and safety of the TiDB documentation related to the Titan storage engine. It clarifies the recommended and safe procedure for disabling Titan in TiKV, explicitly warning against a previously documented but potentially dangerous configuration change for older TiDB versions. Additionally, it updates the documentation to reflect recent changes in the default behavior of Titan's enabled configuration, providing important context for users upgrading or deploying new TiDB clusters.
Highlights
- Documentation Update for Titan Configuration: The pull request updates the documentation for configuring and disabling Titan, a storage engine used by TiKV, specifically for TiDB v8.1 and later versions.
- Revised Titan Disabling Procedure: The steps for disabling Titan have been revised to remove unrecommended actions. It now explicitly advises against directly setting
rocksdb.titan.enabledtofalsefor TiDB versions earlier than v8.5.0 due to potential TiKV crashes. The documentation emphasizes that modifyingrocksdb.defaultcf.titan.blob-run-modeis the primary and safer method. - Clarification on
rocksdb.titan.enabledDefault: The documentation for therocksdb.titan.enabledconfiguration item has been updated to reflect that its default value changed fromfalsetotruestarting from TiDB v7.6.0, meaning Titan is now enabled by default in newer versions. It also clarifies upgrade behavior for existing clusters.
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Code Review
This pull request updates documentation regarding Titan configuration, specifically removing unrecommended steps for disabling Titan and clarifying the behavior of the rocksdb.titan.enabled configuration. The primary concern is the presence of merge conflict markers in both modified files, which must be resolved. Additionally, some sentences could be simplified for better readability.
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| To disable Titan, perform the following steps: | ||
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| 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:** | ||
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| > 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)) |
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This file contains merge conflict markers (<<<<<<<, =======, >>>>>>>) on lines 121-129. These must be resolved before the pull request can be merged.
Please rebase your branch on the target branch to resolve these conflicts.
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| 3. After the compaction is finished, wait until the **Blob file count** metrics under **TiKV-Details/Titan - kv** decrease to `0`. | |||
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| <<<<<<< HEAD | |||
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This file contains a merge conflict marker (<<<<<<< HEAD). This must be resolved before the pull request can be merged.
Please rebase your branch on the target branch to resolve this conflict.
| ======= | ||
| >>>>>>> 445dea0c18 (titan-configuration: remove the unrecommended steps of updating TiKV configuration (#21217)) |
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This file contains merge conflict markers (=======, >>>>>>>). These must be resolved before the pull request can be merged.
Please rebase your branch on the target branch to resolve these conflicts.
tikv-configuration-file.md
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| + 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)) |
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This file contains merge conflict markers (<<<<<<<, =======, >>>>>>>) on lines 1159-1161 and 1162-1175. These must be resolved before the pull request can be merged.
Please rebase your branch on the target branch to resolve these conflicts.
tikv-configuration-file.md
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| > | ||
| > - 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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This sentence is long and complex. Breaking it into smaller sentences would improve readability.1
Style Guide References
| > - 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. | |
| If a cluster had Titan enabled before upgrading to v7.6.0 or later, Titan remains enabled after the upgrade. The `min-blob-size` configuration is also retained. If you did not explicitly configure `min-blob-size` before the upgrade, it defaults to `1KiB` to ensure cluster stability. |
Footnotes
qiancai
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/approve |
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[APPROVALNOTIFIER] This PR is APPROVED This pull-request has been approved by: qiancai The full list of commands accepted by this bot can be found here. The pull request process is described here
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This is an automated cherry-pick of #21217
First-time contributors' checklist
What is changed, added or deleted? (Required)
This PR updates release-8.1 docs according to pingcap/docs-cn#20304.
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By default, CHOOSE MASTER ONLY so your changes will be applied to the next TiDB major or minor releases. If your PR involves a product feature behavior change or a compatibility change, CHOOSE THE AFFECTED RELEASE BRANCH(ES) AND MASTER.
For details, see tips for choosing the affected versions (in Chinese).
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Do your changes match any of the following descriptions?