Comment by toddbandrowsky
13 hours ago
You know, I have a hard time seeing how it can be cheaper to run a dataset across a wire rather than just send its grouped results. That's really the problem. I mean, who cares if it takes 100ns to group by on a box when it will take 10 times much for the data to get to it and back.
The fastest possible group by is in sequential memory on that box, fetched from an nvme.
So, when we do group by partitioning, we're really saying, put the groups themselves on different boxes, and group the group by. If it were some utter megaset, the place to put it is on a mainframe, which is basically created for purposes of group by on ridiculous datasets.
At least they have useful technical information in it. Personally really like reading these blog posts.
Measurements and context is so situational that it would be useless anyway imo.
It is not like any DB company is writing blog posts with benchmarks compared to hardware limits. DuckDB had blog posts that has sentences like "You are doing it wrong if you are not using HTTP api on your database in 2026", last time I saw their blog.
I also think object storage is bad in this case. And rust is no a no-no for a database project like this, because it is not ergonomic to do static allocation and arena allocators in rust. And parquet is trash for performance because of many reasons like supported compression formats etc.
> And rust is no a no-no for a database project like this, because it is not ergonomic to do static allocation and arena allocators in rust.
I'm not sure ergonomics matter that much these days, when your agent can write the tedious bits?
You're not wrong: if you know how much memory you need for a single query and can keep the data in attached SSD (so ephemeral SSD on AWS), scaling vertically will give you the fastest execution time.
However horizontal scaling has advantages in that it's easier to scale up and down incrementally. It gives you more aggregate network bandwidth for accessing disaggregated data. Disaggregation allows for independent scaling of compute and storage. Losing a single machine has a marginal impact on the cluster, which can enable you to use cheaper spot resources.
Basically, it's often easier to operate a system designed around horizontal scaling if you need resiliency.
group by is useful with other aggregates like sum, max, and so on.