docs/kb/map-cpu.rst
Due to its thread-per-core architecture, many things within ScyllaDB can be better understood when you look at it on a per-CPU basis. There are Linux tools such as top and perf that can give information about what is happening within a CPU, given a CPU number.
A common mistake users make is to assume that there is a direct and predictable relationship between the ScyllaDB Shard ID and the CPU ID, which is not true.
Starting in version 3.0, ScyllaDB ships with a script to let users know about the mapping between CPUs and ScyllaDB Shards. For users of older versions, a copy of the script can be downloaded from the Seastar git tree <https://raw.githubusercontent.com/scylladb/seastar/master/scripts/seastar-cpu-map.sh>_.
To list the mapping of a specific shard:
.. code-block:: bash
seastar-cpu-map.sh -n scylla -s 0
Output:
.. code-block:: console :class: hide-copy-button
shard: 0, cpu: 1
To list the mapping of all shards:
.. code-block:: bash
seastar-cpu-map.sh -n scylla
Output:
.. code-block:: console :class: hide-copy-button
shard: 0, cpu: 1 shard: 1, cpu: 2 shard: 3, cpu: 4 shard: 2, cpu: 3