Packed Data Support in Haskell(arthi-chaud.github.io)
69 pointsby matt_d19 hours ago5 comments
  • nine_k17 hours ago
    > Introducing the ‘packed’ data format, a binary format that allows using data as it is, without the need for a deserialisation step. A notable perk of this format is that traversals on packed trees is proven to be faster than on ‘unpacked’ trees: as the fields of data structures are inlines, there are no pointer jumps, thus making the most of the L1 cache.

    That is, a "memory dump -> zero-copy memory read" of a subgraph of Haskell objects, allowing to pass such trees / subgraphs directly over a network. Slightly reminiscent of Cap'n Proto.

    • carterschonwald2 hours ago
      One thing that sometimes gets tricky in these things is handling Sub term sharing. I wonder how they implemented it.
    • Zolomon12 hours ago
      They mention this in the article.
    • spockz11 hours ago
      It reminds me more of flat buffers though. Does protobuf also have zero allocation (beyond initial ingestion) and no pointer jumps?
    • 90s_dev13 hours ago
      We are always reinventing wheels. If we didn't, they'd all still be made of wood.
  • NetOpWibbyan hour ago
    Is this like MessagePack for Haskell?
  • tlb8 hours ago
    > the serialised version of the data is usually bigger than its in-memory representation

    I don’t think this is common. Perhaps for arrays of floats serialized as JSON or something. But I can’t think of a case where binary serialization is bigger. Data types like maps are necessarily larger in memory to support fast lookup and mutability.

    • IsTom4 hours ago
      If you use a lot of sharing in immutable data it can grow a lot when serializing. A simple pathological example would be a tree that has all left subtrees same as the right ones. It takes O(height) space in memory, but O(2^height) when serialized.
    • nine_k8 hours ago
      I suppose all self-describing formats, like protobuf, or thrift or, well, JSON are bigger than the efficient machine representation, because they carry the schema in every message, one way or another.
  • lordleft3 hours ago
    This was very well written. Excellent article!
  • gitroom6 hours ago
    honestly i wish more stuff worked this way - fewer hops in memory always makes me happy