# Scylla in a Shared Environment¶

Scylla is designed to utilize all of the resources on the machine it runs on: disk and network bandwidth, RAM, and CPU. This allows you to achieve maximum performance with a minimal node count. In development and test, however, your nodes might be using a shared machine, which Scylla cannot dominate. This article explains how to configure Scylla for shared environments. For some production environment these settings may be preferred as well.

Note that a docker image is a viable and even simpler option - Scylla on dockerhub

## Memory¶

The most important resource that Scylla consumes is memory. By default, when Scylla starts up it inspects the node’s hardware configuration and claims all memory to itself, leaving some reserve for the operating system (OS). This is in contrast to most open-source databases that leave most memory for the OS, but is similar to most commercial databases.

In a shared environment, particularly on a desktop or laptop, gobbling up all the machine’s memory can reduce the user experience, so Scylla allows reducing its memory usage to a given quantity.

On Ubuntu, edit /etc/default/scylla-server, and add --memory 2G to restrict Scylla to 2 gigabytes of RAM.

On Red Hat / CentOS, edit /etc/sysconfig/scylla-server, and add --memory 2G to restrict Scylla to 2 gigabytes of RAM.

If starting Scylla from the command line, simply append --memory 2G to your command line.

## CPU¶

By default, Scylla will utilize all of your processors (in some configurations, particularly on Amazon AWS, it may leave a core for the operating system). In addition, Scylla will pin its threads to specific cores in order to maximize the utilization of the processor on-chip caches. On a dedicated node, this allows maximum throughput, but on a desktop or laptop, it can cause a sluggish user interface.

Scylla offers two options to restrict its CPU utilization:

• --smp N restricts Scylla to N logical cores; for example with --smp 2 Scylla will not utilize more than two logical cores
• --overprovisioned tells Scylla that the machine it is running on is used by other processes; so Scylla will not pin it threads or memory, and will reduce the amount of polling it does to a minimum.

On Ubuntu, edit /etc/default/scylla-server, and add --smp 2 --overprovisioned to restrict Scylla to 2 logical cores.

On Red Hat / CentOS, edit /etc/sysconfig/scylla-server, and add --smp 2 --overprovisioned to restrict Scylla to 2 logical cores.

If starting Scylla from the command line, simply append --smp 2 --overprovisioned to your command line.

## Other Restrictions¶

When starting up, Scylla will check the hardware and operating system configuration to verify that it is compatible with Scylla’s performance requirements. See developer mode for more instructions.

## Summary¶

Scylla comes out of the box ready for production use with maximum performance, but may need to be tuned for development or test uses. This tuning is simple to apply and results in a Scylla server that can coexist with other processes or a GUI on the system

Getting Started