3.7 KiB
MVDS Metadata Field
Version: 0.1.0 (Draft)
Authors: Oskar Thorén oskar@status.im, Dean Eigenmann dean@status.im
Table of Contents
Abstract
In this specification, we describe a method to construct message history that will aid the consistency guarantees of MVDS. Additionally we explain how data sync can be used for more lightweight messages that do not require full synchronization.
Motivation
In order for more efficient synchronization of conversational messages, information should be provided allowing a node to more effectively synchronize the dependencies for any given message.
Format
We introduce the metadata message which is used to convey information about a message and how it SHOULD be handled.
package vac.mvds;
message Metadata {
repeated bytes parents = 1;
bool ephemeral = 2;
}
Nodes MAY transmit a Metadata
message by extending the MVDS message with a metadata
field.
message Message {
bytes group_id = 1;
int64 timestamp = 2;
bytes body = 3;
+ Metadata metadata = 4;
}
Fields
Name | Description |
---|---|
parents |
list of parent message identifier s for the specific message. |
ephemeral |
indicates whether a message is ephemeral or not. |
Usage
parents
This field contains a list of parent message identifier
s for the specific message. It MUST NOT contain any messages as parent whose ack
flag was set to false
. This creates a directed acyclic graph (DAG)1 of persistent messages.
Nodes MAY buffer messages until dependencies are satisfied for causal consistency2, they MAY also pass the messages straight away for eventual consistency3.
A parent is any message before a new message that a node is aware of that has no children.
The number of parents for a given message is bound by [0, N], where N is the number of nodes participating in the conversation, therefore the space requirements for the parents
field is O(N).
If a message has no parents it is considered a root. There can be multiple roots, which might be disconnected, giving rise to multiple DAGs.
ephemeral
When the ephemeral
flag is set to false
, a node MUST send an acknowledgement when they have received and processed a message. If it is set to true
, it SHOULD NOT send any acknowledgement. The flag is false
by default.
Nodes MAY decide to not persist ephemeral messages, however they MUST NOT be shared as part of the message history.
Nodes SHOULD send ephemeral messages in batch mode. As their delivery is not needed to be guaranteed.
Changelog
Version | Comment |
---|---|
0.1.0 | Initial Release |
Footnotes
- https://en.wikipedia.org/wiki/Directed_acyclic_graph
- https://jepsen.io/consistency/models/causal
- https://en.wikipedia.org/wiki/Eventual_consistency
Acknowledgements
- Andrea Maria Piana