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release-8.5: update default value of fix control 52869 #21744

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release-8.5: update default value of fix control 52869 #21744

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f5cdc53
update optimizer fix control 52869 default value
time-and-fate Jun 24, 2026
8b48b77
Update optimizer-fix-controls.md
qiancai Jun 25, 2026
046391c
clarify index merge limitation behavior for fix control 52869
time-and-fate Jul 3, 2026
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2 changes: 1 addition & 1 deletion optimizer-fix-controls.md
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Expand Up @@ -103,7 +103,7 @@ SET SESSION tidb_opt_fix_control = '44262:ON,44389:ON';

### [`52869`](https://github.com/pingcap/tidb/issues/52869) <span class="version-mark">从 v8.1.0 版本开始引入</span>

- 默认值：`OFF`
- 默认值：`ON`。在 v8.5.7 之前的版本中，默认值为 `OFF`。
- 可选值：`ON`、`OFF`
- 如果查询有除了全表扫描以外的单索引扫描方式可以选择，优化器不会自动选择索引合并。详情请参考[用 EXPLAIN 查看索引合并的 SQL 执行计划](/explain-index-merge.md#示例)中的**注意**部分。
- 打开此开关后，这个限制会被解除。解除此限制能让优化器在更多查询中自动选择索引合并，但也有可能忽略其他更好的执行计划，因此建议在解除此限制前针对实际场景进行充分测试，确保不会带来性能回退。
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