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Update system-variables.md
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hfxsd authored and ti-chi-bot committed Aug 26, 2024
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Expand Up @@ -1694,7 +1694,7 @@ mysql> SELECT job_info FROM mysql.analyze_jobs ORDER BY end_time DESC LIMIT 1;
- Unit: Rows
- This variable is used to set the batch size during the `re-organize` phase of the DDL operation. For example, when TiDB executes the `ADD INDEX` operation, the index data needs to backfilled by `tidb_ddl_reorg_worker_cnt` (the number) concurrent workers. Each worker backfills the index data in batches.
- If `tidb_ddl_enable_fast_reorg` is set to `OFF`, `ADD INDEX` is executed as a transaction. If there are many update operations such as `UPDATE` and `REPLACE` in the target columns during the `ADD INDEX` execution, a larger batch size indicates a larger probability of transaction conflicts. In this case, it is recommended that you set the batch size to a smaller value. The minimum value is 32.

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[vale] reported by reviewdog 🐶 [PingCAP.Ambiguous] Consider using a clearer word than 'many' because it may cause confusion. Raw Output: {"message": "[PingCAP.Ambiguous] Consider using a clearer word than 'many' because it may cause confusion.", "location": {"path": "system-variables.md", "range": {"start": {"line": 1696, "column": 111}}}, "severity": "INFO"}
- If the transaction conflict does not exist, or if `tidb_ddl_enable_fast_reorg` is set to `ON`, you can set the batch size to a large value. This makes data backfilling faster but also increases the write pressure on TiKV. For a proper batch size, you also need to refer to the value of `tidb_ddl_reorg_worker_cnt`. See [Interaction Test on Online Workloads and `ADD INDEX` Operations](/benchmark/online-workloads-and-add-index-operations.md) for reference.
- If the transaction conflict does not exist, or if `tidb_ddl_enable_fast_reorg` is set to `ON`, you can set the batch size to a large value. This makes data backfilling faster but also increases the write pressure on TiKV. For a proper batch size, you also need to refer to the value of `tidb_ddl_reorg_worker_cnt`. See [Interaction Test on Online Workloads and `ADD INDEX` Operations](https://docs.pingcap.com/tidb/dev/online-workloads-and-add-index-operations) for reference.

### tidb_ddl_reorg_priority

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