Performance Degradation After Upgrading from 6.2 to 6.5

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This topic has been translated from a Chinese forum by GPT and might contain errors.

Original topic: 6.2升级到6.5之后变慢了

| username: Running

After upgrading from 6.2 to 6.5, the query speed of TiFlash has slowed down; previously it took 3 seconds for 700 million, now it takes 8 seconds.

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| username: 裤衩儿飞上天 | Original post link
  1. What is the value of tiflash_fastscan in version 6.5?
  2. Was fast scan enabled before the upgrade (version 6.2)?
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| username: Running | Original post link

The default value of tidb_enable_clustered_index is INT_ONLY, which means that only tables with integer primary keys will use clustered indexes by default.

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| username: Running | Original post link

Previously, TiFlash was already enabled. Now, the only noticeable improvement is that count operations are faster, but other group queries have become slower.

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| username: 裤衩儿飞上天 | Original post link
  1. I meant, did you use ALTER TABLE … SET TiFLASH MODE … to set fastscan in version 6.2?
  2. Do you have a comparison of execution time and execution plan before and after the upgrade?
  3. Currently, I can only think of the impact brought by the tiflash_fastscan parameter, because this setting method was deprecated in version 6.3, and the settings in version 6.2 will become invalid.
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| username: Running | Original post link

This parameter does have some impact. After adjustment, the performance is basically on par with version 6.2.

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| username: 裤衩儿飞上天 | Original post link

Note: If the FastScan feature is enabled (set to ON), TiFlash can provide more efficient query performance, but it does not guarantee the accuracy and data consistency of the query results.

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| username: system | Original post link

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