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Scylla memory usage might be larger than the data set used.
For example:
The data size is 19GB, but Scylla uses 220G memory.
Scylla uses available memory to cache your data. Scylla knows how to dynamically manage memory for optimal performance, for example, if many clients connect to Scylla, it will evict some data from the cache to make room for these connections, when the connection count drops again, this memory is returned to the cache.
To limit the memory usage you can start scylla with --memory parameter.
Alternatively, you can specify the amount of memory ScyllaDB should leave to the OS with --reserve-memory parameter. Keep in mind that the amount of memory left to the operating system needs to suffice external scylla modules, such as scylla-jmx, which runs on top of JVM.
On Ubuntu, edit the /etc/default/scylla-server.
On Red Hat / CentOS, edit the /etc/sysconfig/scylla-server.
For example:
SCYLLA_ARGS="--log-to-syslog 1 --log-to-stdout 0 --default-log-level info --collectd-address=127.0.0.1:25826 --collectd=1 --collectd-poll-period 3000 --network-stack posix --memory 2G --reserve-memory 2G
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