Holochain Forum

Anchor

Problem

Discovering data in a DHT is hard because data is spread out over many nodes and can’t be queried.

Solution

Create easy-to-find starting points that act as bases for links to other data. Eventually the entire DHT becomes a graph database.

Examples

  • Each agent has a built-in anchor: their agent ID entry. They can link to blog articles they’ve written, for example, or friends they know.
  • A hashtag: a simple string that links to all related content.
  • A short ‘ID code’ that can be shared via text messaging, printed materials, email, or other media that would require retyping or copy/pasting. This is a lot easier and less prone to corruption than sharing a full hash.
  • The hash of a known value in another DHT as a sort of ‘foreign key’.
  • A value that is hard-coded into the DNA itself (see Symbol Anchor).
  • A tree of values that link to their parents, allowing users to traverse the entire tree by starting at the root node (see Anchor Tree).

Warnings

Antipattern : If you expect a given anchor to have a lot of links on it, this could create a ‘hot spot’ in the DHT neighbourhood that stores the anchor: the nodes in that neighbourhood will be responsible for storing all the links and responding to requests for them. Consider breaking up one anchor into multiple anchors (for instance, twenty-six anchors that link to entries starting with “a”, “b”, “c”, etc). This can increase query time but doesn’t usually hurt write time.