presto-admin | A tool to install , configure and manage Presto installations

The default for query.max-memory-per-node is 10% of the available heap memory. The default for this property is set here:

https://github.com/prestosql/presto/blob/master/presto-main/src/main/java/io/prestosql/memory/NodeMemoryConfig.java#L35

IIRC we set the default value so you could have a few large queries running in a cluster. The exact number isn't clear from this value alone. If you take a look at the configurations in the file linked above you will see that the system first reserves 30% of the heap for "unaccounted memory allocations", because Presto doesn't track all allocations. Then the query.max-memory-per-node is only a limit on "user" memory, which is memory controllable by the query author such as group by and join hash tables. This value does not include input and output buffers which are automatically managed by Presto.

With all of that put together, I would expect with the default values you can run 3-5 large queries concurrently on the code.

As for how you want to set these, it really depends on your workload. If you expect to have a large mixed workload, the defaults may work for you. If you want to be able to dedicate the entire cluster to a single worker, you can increase the values to near the heap size (make sure to leave head room for untracked allocations).