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Jun 4, 2024
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statistics: update the note for sampling rate (#17662) #17748

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14 changes: 1 addition & 13 deletions statistics.md
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Expand Up @@ -240,21 +240,9 @@ Before v5.3.0, TiDB uses the reservoir sampling method to collect statistics. Si

The current sampling rate is calculated based on an adaptive algorithm. When you can observe the number of rows in a table using [`SHOW STATS_META`](/sql-statements/sql-statement-show-stats-meta.md), you can use this number of rows to calculate the sampling rate corresponding to 100,000 rows. If you cannot observe this number, you can use the sum of all the values in the `APPROXIMATE_KEYS` column in the results of [`SHOW TABLE REGIONS`](/sql-statements/sql-statement-show-table-regions.md) of the table as another reference to calculate the sampling rate.

<CustomContent platform="tidb">

> **Note:**
>
> Normally, `STATS_META` is more credible than `APPROXIMATE_KEYS`. However, after importing data through the methods like [TiDB Lightning](https://docs.pingcap.com/tidb/stable/tidb-lightning-overview), the result of `STATS_META` is `0`. To handle this situation, you can use `APPROXIMATE_KEYS` to calculate the sampling rate when the result of `STATS_META` is much smaller than the result of `APPROXIMATE_KEYS`.

</CustomContent>

<CustomContent platform="tidb-cloud">

> **Note:**
>
> Normally, `STATS_META` is more credible than `APPROXIMATE_KEYS`. However, after importing data through TiDB Cloud console (see [Import Sample Data](/tidb-cloud/import-sample-data.md)), the result of `STATS_META` is `0`. To handle this situation, you can use `APPROXIMATE_KEYS` to calculate the sampling rate when the result of `STATS_META` is much smaller than the result of `APPROXIMATE_KEYS`.

</CustomContent>
> Normally, `STATS_META` is more credible than `APPROXIMATE_KEYS`. However, when the result of `STATS_META` is much smaller than the result of `APPROXIMATE_KEYS`, it is recommended that you use `APPROXIMATE_KEYS` to calculate the sampling rate.

### The memory quota for collecting statistics

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