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Change the default value of feedback-probability (#3895) #3902

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Sep 14, 2020
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Change the default value of feedback-probability (#3895) #3902

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8 changes: 6 additions & 2 deletions statistics.md
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Expand Up @@ -106,7 +106,11 @@ Three system variables related to automatic update of statistics are as follows:

When the ratio of the number of modified rows to the total number of rows of `tbl` in a table is greater than `tidb_auto_analyze_ratio`, and the current time is between `tidb_auto_analyze_start_time` and `tidb_auto_analyze_end_time`, TiDB executes the `ANALYZE TABLE tbl` statement in the background to automatically update the statistics of this table.

When the query is executed, TiDB collects feedback with the probability of `feedback-probability` and uses it to update the histogram and Count-Min Sketch. You can modify the value of `feedback-probability` in the configuration file. The default value is `0.0`.
When the query is executed, TiDB collects feedback with the probability of `feedback-probability` and uses it to update the histogram and Count-Min Sketch. You can modify the value of `feedback-probability` in the configuration file. The default value is `0.05`. You can set the value to `0.0` to disable this feature.

> **Note:**
>
> If you set the value of `feedback-probability` to `0` in the configuration file, a failure will occur and an error will be reported. To disable `feedback-probability`, you need to set the value to `0.0`.

### Control `ANALYZE` concurrency

Expand Down Expand Up @@ -307,4 +311,4 @@ Syntax:
LOAD STATS 'file_name'
```

`file_name` is the file name of the statistics to be imported.
`file_name` is the file name of the statistics to be imported.