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This topic has been translated from a Chinese forum by GPT and might contain errors.Original topic: tiflash 未使用
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Version: 5.2
Description: After adding a table to TiFlash, the TiFlash node is not used in the execution plan.
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The main reason is that the default value of the tidb_distsql_scan_concurrency parameter in TiDB 4.0 is 15, while in TiDB 5.0 it is 4. This parameter controls the number of concurrent threads used for scanning data in TiDB. You can try adjusting this parameter to see if it improves performance.
TiFlash is a columnar storage, and it is generally used only when aggregate functions are involved, such as count and sum.
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You can start by writing a simple single-table query to try it out.
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You can try writing the hint this way:
However, generally, if the optimization analysis uses TiKV, it means that TiKV is the optimal solution for the current query. It doesn’t necessarily mean that TiFlash will be used just because TiFlash is enabled.
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Using the curdate() function results in a full table scan, but switching to left(now(),10) allows the use of an index. Is there something special about the curdate() function?
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