feat: store sync spec

standards/core/store-sync.md

@@ -0,0 +1,60 @@
+---
+title: WAKU-STORE-SYNC
+name: Waku Store Synchronization
+editor: Simon-Pierre Vivier <simvivier@status.im>
+contributors:
+---
+
+## Abstract
+
+This document describe the strategy Waku Store node will employ to stay synchronized.
+The goal being that all store nodes eventually archive the same set of messages.
+
+## Background / Rationale / Motivation
+
+Message propagation in the network is not perfect,
+even with GossipSub mechanisms to detect missed messages.
+Nodes can also go offline for various reason outside our control.
+Store nodes that want to provide a good service must be able to remedy situations like these.
+By having store nodes syncronize with each other through various protocols,
+the set of archived messages network wide will be eventually consistent.
+
+## Theory / Semantics
+
+The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “NOT RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in [RFC 2119](https://www.ietf.org/rfc/rfc2119.txt).
+
+Various protocols and features that help with message consistency are described below.
+
+### Store Resume
+
+<!-- restating this as a heuristic rather than a high-level description of functionality allows the spec to be useful for new implementers -->
+
+This feature allow a node to fill the gap in messages for the period it was last offline.
+At startup, a node use the Store protocol to query a random node for
+the time interval since it was last online.
+Messages returned by the query are then added to the node local archive storage.
+It is RECOMMENDED to limit the time interval to a maximum of 6 hours.
+
+### Waku Sync
+
+<!--
+For the new version. "think of a specification as a heuristic/set of directives that almost form a kind of pseudocode. This becomes easier if you use the RFC keywords for each directive"
+-->
+
+Nodes that stay online can still miss messages.
+[Waku Sync](https://github.com/waku-org/specs/blob/master/standards/core/sync.md) is the protocol used to find those message hashes by periodically syncing with random nodes.
+It is RECOMMENDED to trigger a sync with a random peer every 5 minutes for a time range of the last hour.
+After both message hash sets are reconciled,
+the Store protocol SHOULD be used to reciprocally query the other node with the message hash differences found.
+Messages returned by the query MUST be added to the node local Waku sync and archive storage.
+
+<!-- TODO add the number of node to sync with -->
+
+## Copyright
+
+Copyright and related rights waived via [CC0](https://creativecommons.org/publicdomain/zero/1.0/).
+
+
+## References
+
+- [Waku Sync](https://github.com/waku-org/specs/blob/master/standards/core/sync.md)