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tikv / titan: Add note for disabling titan #20996

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qiancai May 21, 2025
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8 changes: 6 additions & 2 deletions storage-engine/titan-configuration.md
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Expand Up @@ -138,7 +138,7 @@
- When the option is set to `read-only`, all newly written values are written into RocksDB, regardless of the value size.
- When the option is set to `fallback`, all newly written values are written into RocksDB, regardless of the value size. Also, all compacted values stored in the Titan blob file are automatically moved back to RocksDB.

To fully disable Titan for all existing and future data, you can follow these steps. Note that you can skip Step 2 because it greatly impacts 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.
To disable Titan for all existing and future data, you can follow these steps. Note that you can skip Step 2 because it greatly impacts 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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[vale] reported by reviewdog 🐶
[PingCAP.Ambiguous] Consider using a clearer word than 'much' because it may cause confusion.

Raw Output:
{"message": "[PingCAP.Ambiguous] Consider using a clearer word than 'much' because it may cause confusion.", "location": {"path": "storage-engine/titan-configuration.md", "range": {"start": {"line": 141, "column": 336}}}, "severity": "INFO"}

1. Update the configuration of the TiKV nodes you wish to disable Titan for. You can update configuration in two methods:

Expand Down Expand Up @@ -167,7 +167,11 @@

3. After the compaction is finished, wait for the **Blob file count** metrics under **TiKV-Details**/**Titan - kv** to decrease to `0`.

4. Update the configuration of these TiKV nodes to disable Titan.
4. For TiDB v8.5.0 or a later version, update the configuration of these TiKV nodes to disable Titan.

> **Warning:**
>
> For versions earlier than v8.5.0, it is recommended to skip this step, because it might cause TiKV to crash. In these earlier versions, you can disable Titan directly by following Step 1. There is no performance difference between the configuration changes in Step 1 and the following changes in this step after the data migration is complete.

```toml
[rocksdb.titan]
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