# Map CPUs to ScyllaDB Shards

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).

## Examples of usage

To list the mapping of a specific shard:

```bash
seastar-cpu-map.sh -n scylla -s 0
```

Output:

```console
shard: 0, cpu: 1
```

To list the mapping of all shards:

```bash
seastar-cpu-map.sh -n scylla
```

Output:

```console
shard: 0, cpu: 1
shard: 1, cpu: 2
shard: 3, cpu: 4
shard: 2, cpu: 3
```