# `Finch.Pool.Strategy.Hash`
[🔗](https://github.com/sneako/finch/blob/v0.23.0/lib/finch/pool/strategy/hash.ex#L1)

Selects a pool worker by hashing a key, so the same key always maps to the same worker.

Useful for connection affinity: e.g. team IDs, session tokens, or any scenario where
routing the same logical entity to the same connection is beneficial.

This strategy takes a `key` and selects a worker using `:erlang.phash2/2`.
This ensures that tasks classified under the same key will be delivered to the same worker,
which is useful to classify events by key and work on them sequentially on the worker,
distributing different keys across different workers.

If no key is given, it uses `self()` when constructing a state.

## Example

    key = Finch.Pool.Strategy.Hash.new()
    Finch.request(req, MyFinch, pool_strategy: {Finch.Pool.Strategy.Hash, key})
    ## equivalent to the above
    Finch.request(req, MyFinch, pool_strategy: {Finch.Pool.Strategy.Hash, self()})

    key = Finch.Pool.Strategy.Hash.new(tenant_id)
    Finch.request(req, MyFinch, pool_strategy: {Finch.Pool.Strategy.Hash, key})
    ## equivalent to the above
    Finch.request(req, MyFinch, pool_strategy: {Finch.Pool.Strategy.Hash, tenant_id})

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*Consult [api-reference.md](api-reference.md) for complete listing*