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Data Synchronization

Assets can make use of a versioned mechanism for synchronizing data files that are larger than would be comfortable to place into a Git repository. These are called HTTPSynchronization and are used in assets like so:

local syncedDirectory = asset.syncedResource({
    Name = "General SPK Kernels",
    Type = "HttpSynchronization",
    Identifier = "general_spk",
    Version = 1
})

This command will download all files that correspond to the general_spk identifier for the file version 1 and provide the folder where the files were downloaded as a return value, synchedDirectory in this case. This document describes how the identifier and version number are resolved through a network of servers that run custom NodeJS software called BigBang.

Data endpoint usage

OpenSpace uses one of the BigBang servers as an endpoint, the setting of which is done in the openspace.cfg file:

    Sync = {
        SynchronizationRoot = "${SYNC}",
        HttpSynchronizationRepositories = {
            "http://data.openspaceproject.com/request"
            -- "http://openspace.sci.utah.edu/request"
        }
    },

When requesting general_spk in file version 1, OpenSpace will perform a web request to the provided repository and the request contains all information necessary to resolve the request. In this case, the complete URL would be: http://data.openspaceproject.com/request?identifier=general_spk&file_version=1&application_version1. This URL will contain a list of files thare are associated with this identifier and version, and OpenSpace will download all files contained in this file.

NB: The application version is used to future proof this setup and currently no other value than 1 is supported

Server arrangement

Each BigBang server has a local mapping of (identifier, version, application version) to a list of files and a list of other servers it can ask for values that it does not recognize. This builds a graph of BigBang servers that collectively contain all of the file information for all supported identifiers.

Usage example

In this example, there are three different OpenSpace clients that each have a separate BigBang node as their endpoint. The three nodes in this example, data.openspaceproject.com, data2.openspaceproject.com, and data3.openspaceproject.com are configured asymmetrically. data knows about data2 and data3, data2 knows about data and data3, but data3 is only aware of data2.

Each color in this image corresponds to a single request call to the endpoint and the different colors represent different usage scenarios:

  1. Green: OpenSpace requests an identifier and the endpoint BigBang servers knows about the identifier/version combination locally
  2. Purple: The same as green, but the location of the files might be different due to proximity of the server to the requester. (NB: The servers are configured so that the content of the files are the same, even if they are provided at different URLs).
  3. Orange: The same as green and purple, but without much detail.
  4. Red: OpenSpace requests an identifier, but the endpoint server does not know about the identifier itself and has to get referrals from its known servers. One of these directly knows about the identifier/version and returns them
  5. Blue: The same as red, but now neither the endpoint, nor a directly connected servers knows about the identifier, so the connected servers needs to enquire recursively.

Network messages in this example are numbered on the order in which they occur. If two messages happen simultaneously, they are subdivided by letters (3a and 3b) are done in parallel and are both finished before 4 can happen.