Clickhouse queries - low memory usage

[sparsh sidana]

I've run  complex select query on my table involving joins. When I do a show processList it shows the following data:

Peak Memory Usage: 195005658

memory usage: 169827955

total rows approx: 186523648

read bytes: 451899808

read rows: 78696623

At the end of the query i get this output:

5 rows in set. Elapsed: 7.340 sec. Processed 369.17 million rows, 2.25 GB (50.30 million rows/s., 306.23 MB/s.)

It takes 7.3 sec to execute the query. I am trying to figure out why the memory utilization is low while running the query and is there way that I could increase it so that the performance improves?

Also, I haven't set any max memory utilization parameters in configs. It's using the default value

[Maxim Ulanovskiy]

Hi Sparsh,

By default, CH allows 10GB per query.

Your query just doesn't need that much RAM and performance issues are due to other reasons.

You should rather look into query/schema optimization.

One thing I can say right away is that JOIN is one of the most resource-intensive operations for any DB and Clickhouse offers a few ways to optimize it e.g. Dictionaries.

Regards,

Max

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