> For the complete documentation index, see [llms.txt](https://dcf.gitbook.io/dcf/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://dcf.gitbook.io/dcf/guide/data-serializing.md).

# Data Serializing

Data in RDD may be serialized in serveral cases:

1. To persist data on disk or off-heap memory.
2. To transfer data for repartition
3. To transfer result to master & client
4. To get a hash value for combineByKey/distinct

Serialize will comes with two method:

### V8.serialize()/V8.deserialize()

For case 1-3, data will be serialized and deserialized later. [V8.serialize()](https://nodejs.org/api/v8.html#v8_v8_serialize_value) is the best function for this. It can deal many type of data:

1. primitive types: undefined, null, number, boolean, string, Symbol
2. array, object literal
3. Date, RegExp, Set, Map
4. Buffer/typed arrays

So in generally speaking you could use any type except custom classes.

### Key Serialize

But there's a problem for V8.serialize: sometimes it gives different result for same input, especially for splitted string. So when we need another serialize function for combineByKey/distinct.

The function may change in future, but these types are guaranteed safe as key types:

1. primitive types except Symbol: null, number, boolean, string
2. array, object literal

> Current version of dcf use a custom version of [msgpack5](https://www.npmjs.com/package/msgpack5) for key serialize, which support undefined value.