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This topic has been translated from a Chinese forum by GPT and might contain errors.Original topic: tiflash distinct 非常慢，求优化
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username: LKLK
[TiDB Usage Environment] Production Environment / Testing / PoC
[TiDB Version]
[Reproduction Path] What operations were performed when the issue occurred
[Encountered Issue: Problem Phenomenon and Impact]
[Resource Configuration]
[Attachments: Screenshots / Logs / Monitoring]
In the online v5.4.1 environment, queries using TiFlash with distinct are very slow. Even after setting set @@tidb_opt_distinct_agg_push_down = 1;, the performance is still very slow. However, removing distinct makes it very fast. How can this be optimized?
SELECT * FROM (select login_date, sum(login_cnt) as login_cnt, count(distinct id) as active_user from log_login_1051 where login_date >= '2022-11-29' AND login_date <= '2022-12-28' group by login_date) tmp ORDER BY login_date ASC LIMIT 1000 OFFSET 0;
MySQL [xxx]> select count(1) from log_login_1051;
+-----------+
| count(1) |
+-----------+
| 242504116 |
+-----------+
1 row in set (0.67 sec)
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