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optimizer-fix-controls: Add optimizer fix control 47400 for controlling zero estRows #18587

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optimizer-fix-controls: Add optimizer fix control 47400 for controlling zero estRows #18587

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Add fix control 47400
terry1purcell Aug 14, 2024
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7 changes: 7 additions & 0 deletions optimizer-fix-controls.md
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Expand Up @@ -71,6 +71,13 @@ SET SESSION tidb_opt_fix_control = '44262:ON,44389:ON';
- This variable sets the threshold for the optimizer's heuristic strategy to select access paths. If the estimated rows for an access path (such as `Index_A`) is much smaller than that of other access paths (default `1000` times), the optimizer skips the cost comparison and directly selects `Index_A`.
- `0` means to disable this heuristic strategy.

### [`47400`](https://github.com/pingcap/tidb/issues/47400) <span class="version-mark">New in v8.4.0</span>

- Default value: `ON`
- Possible values: `ON`, `OFF`
- This variable sets the minimum row estimate that the optimizer will allow. Due to challenges that all optimizers face in accuracy in estimating the number of qualified rows for each plan step in a query plan, it is common that an optimizer will set a lower limit. The default (`ON`) implemented in TiDB is the new behavior and is consistent with other databases.
- `OFF` means disable this minimum value, which is the prior behavior (before this enhancement and fix-control).
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### [`52869`](https://github.com/pingcap/tidb/issues/52869) <span class="version-mark">New in v8.1.0</span>

- Default value: `OFF`
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