High latency on high QPS use case

We noticed the latency from offline server becomes high when qps is high (e.g. more than 1000 qps per server host).
The query pattern is:
```
SELECT sum(count) FROM table1 WHERE column1 IN ("aa", "ab", "ad", ..., "zz")
```
This page is used to keep track of the methods we've tried to optimize the performance.