> ## Documentation Index
> Fetch the complete documentation index at: https://private-7c7dfe99-mintlify-1d264819.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# CityHash

> Native protocol hash

ClickHouse uses **one of the previous** versions of [CityHash from Google](https://github.com/google/cityhash).

<Info>
  CityHash has changed the algorithm after we have added it into ClickHouse.

  CityHash documentation specifically notes that the user shouldn't rely on
  specific hash values and shouldn't save it anywhere or use it as a sharding key.

  But as we exposed this function to the user, we had to fix the version of CityHash (to 1.0.2). And now we guarantee that the behaviour of CityHash functions available in SQL won't change.

  — Alexey Milovidov
</Info>

<Info>
  **Note**

  Current version of Google's CityHash [differs](https://github.com/ClickHouse/ClickHouse/issues/8354) from ClickHouse `cityHash64` variant.

  Don't use `farmHash64` to get Google's CityHash value! [FarmHash](https://opensource.googleblog.com/2014/03/introducing-farmhash.html) is a successor to CityHash, but they're not fully compatible.

  | String                                                     | ClickHouse64         | CityHash64          | FarmHash64           |
  | ---------------------------------------------------------- | -------------------- | ------------------- | -------------------- |
  | `Moscow`                                                   | 12507901496292878638 | 5992710078453357409 | 5992710078453357409  |
  | `How can you write a big system without C++?  -Paul Glick` | 6237945311650045625  | 749291162957442504  | 11716470977470720228 |
</Info>

Also see [Introducing CityHash](https://opensource.googleblog.com/2011/04/introducing-cityhash.html) for description and
reasoning behind creation. TL;DR **non-cryptographic** hash that is faster than [MurmurHash](http://en.wikipedia.org/wiki/MurmurHash), but more complex.

<h2 id="implementations">
  Implementations
</h2>

<h3 id="go">
  Go
</h3>

You can use [go-faster/city](https://github.com/go-faster/city) Go package that implements both variants.