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Re: Varlena with recursive data structures?

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Hi Karl,

I'm going down this road myself.  In addition to the files Tom Lane pointed out there is also some helpful documentation here:

https://www.postgresql.org/docs/current/storage-toast.html#STORAGE-TOAST-INMEMORY

On Wed, Jan 16, 2019 at 2:09 PM Sam Patterson <katoriasdev@xxxxxxxxx> wrote:
Hi all,

I've recently started developing an extension for Postgres for which I'll need to create a new variable-length base type. The type will require a tree-like structure in order to parse sufficiently, which of course probably means having some sort of recursive data structure, like a struct that has members which are pointers to itself for child nodes. After doing some research, specifically looking at how other variable-length data types store their data, it seems almost all of them store the data in a binary representation, using bit masks and offsets etc in order to store/access the data whilst having an in-memory representation that's used to manipulate the data.

I presume the purpose for using this approach is because all the data in a varlena type has to be contiguous, and the moment you start using pointers this is no longer possible. So my question is, given a structure that looks something like this,

typedef struct Node 
{
    char *data;
    Node *left;
    Node *right;
} Node;

am I right in saying that I wouldn't be able to store that representation on-disk, but instead I'd have to transform it into some binary representation and back again when writing/reading respectively, are there any alternatives?

Regards,

Karl

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