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statistics: update the note for sampling rate (#17467) #17554

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ti-chi-bot merged 2 commits into from
Jun 4, 2024
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statistics: update the note for sampling rate (#17467) #17554

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Update statistics.md
qiancai May 29, 2024
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Update statistics.md
qiancai Jun 4, 2024
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2 changes: 1 addition & 1 deletion statistics.md
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Expand Up @@ -113,7 +113,7 @@ ANALYZE TABLE TableNameList [WITH NUM BUCKETS|TOPN|CMSKETCH DEPTH|CMSKETCH WIDTH
>
> 目前采样率基于自适应算法进行计算。当你通过 [`SHOW STATS_META`](/sql-statements/sql-statement-show-stats-meta.md) 可以观察到一个表的行数时，可通过这个行数去计算采集 10 万行所对应的采样率。如果你观察不到这个值，可通过表 [`SHOW TABLE REGIONS`](/sql-statements/sql-statement-show-table-regions.md) 结果中所有 `APPROXIMATE_KEYS` 列值的总和作为另一个参考来计算采样率。
>
> 通常情况下，`STATS_META` 相对 `APPROXIMATE_KEYS` 更可信，但是通过 [TiDB Lightning](/tidb-lightning/tidb-lightning-overview.md) 等方式导入数据结束后，`STATS_META` 结果是 `0`。为了处理这个情况，你可以在 `STATS_META` 的结果远小于 `APPROXIMATE_KEYS` 的结果时，使用 `APPROXIMATE_KEYS` 计算采样率。
> 通常情况下，`STATS_META` 相对 `APPROXIMATE_KEYS` 更可信，但当 `STATS_META` 的结果远小于 `APPROXIMATE_KEYS` 的结果时，推荐使用 `APPROXIMATE_KEYS` 计算采样率。

#### 收集部分列的统计信息

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