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How to keep an external database in-sync with a Mesh node

This guide will walk you through syncing an external database with a Mesh node so that the external database's state mirrors that of the Mesh node (and vice-versa). Whenever new orders are discovered or added to Mesh, they are inserted into the database. If an order is filled, cancelled, or has its fillability changed it is updated or removed from the database. We are assuming that your database is storing both the order itself and the remaining fillable amount (i.e., its fillableTakerAssetAmount).

High-level architecture

Mesh is a stand-alone daemon that will be running independently from the rest of your infrastructure. Your backend will communicate with the Mesh node over WebSockets using JSON-RPC. This is a bi-directional connection allowing both your server to notify Mesh of new orders, and Mesh to notify your server of order updates.

Initial sync

When first connecting the DB and Mesh node, we first need to make sure both have the same orders and order-relevant state stored. We do this with the following steps:

1. Subscribe to Mesh

Subscribe to the Mesh node's orders subscription over a WS connection. This can be done using our golang or Typescript/Javascript clients or any other JSON-RPC WebSocket client. Whenever you receive an order event from this subscription, make the appropriate updates to your DB. Each order event has an associated OrderEventEndState.

End state DB operation
ADDED Insert

Note: Updates refer to updating the order's fillableTakerAssetAmount in the DB.

Note 2: If we receive any event other than ADDED and FILLABILITY_INCREASED for an order we do not find in our database, we ignore the event and noop.

2. Get all orders currently stored in Mesh

There might have been orders stored in Mesh that the DB doesn't know about at this time. Because of this, we must fetch all currently stored orders in the Mesh node and upsert them in the database. This can be done using the mesh_getOrders JSON-RPC method. This method creates a snapshot of the Mesh node's internal DB of orders when first called, and allows for subsequent paginated requests against this snapshot. Because we are already subscribed to order events, any new orders added/removed after the snapshot is made will be discovered via that subscription.

Note: The Mesh Typescript client has a convenience method that does the multiple paginated requests for you under-the-hood. You can simply call the getOrders method.

3. Add all database orders to the Mesh node

Since there might also be orders added to the database that Mesh doesn't know about, we must also add all DB orders to Mesh. We can do this using the mesh_addOrders JSON-RPC method. This method accepts an array of signed 0x orders and returns which have been accepted and rejected. The accepted orders are returned with their fillableTakerAssetAmount and so these amounts should be updated in the database. Rejected orders are rejected with a specific RejectedOrderStatus, including an identifying code.

Code Reason Should be retried?
EthRPCRequestFailed, CoordinatorRequestFailed, CoordinatorEndpointNotFound, InternalError Failure to validate the order Yes
MaxOrderSizeExceeded, OrderMaxExpirationExceeded, OrderForIncorrectChain, SenderAddressNotAllowed Failed Mesh-specific criteria No
OrderHasInvalidMakerAssetData, OrderHasInvalidTakerAssetData, OrderHasInvalidSignature, OrderUnfunded, OrderCancelled, OrderFullyFilled, OrderHasInvalidMakerAssetAmount, OrderHasInvalidTakerAssetAmount, OrderExpired Invalid or unfillable order No

If an order was rejected with a code related to the "failure to validate the order" reason above, you can re-try adding the order to Mesh after a back-off period. For all other rejection reasons, the orders should be removed from the database.

4. Handle dropped connections

After performing the first 3 steps above, the Mesh node and database will be in-sync, and continue to remain in-sync thanks to the active order event subscription. If any new orders are added to the database, they will also need to be added to Mesh of course. But what if the WebSocket connection to the Mesh node goes down? In that case, it must be re-established and steps 1, 2 & 3 must be performed once again.

Note: The Mesh Typescript client takes care of re-connecting and re-establishing all active subscriptions once it detects a disconnection. You can subscribe to a reconnected event using the onReconnected method. Whenever this callback is fired is when you need to re-run steps 2 and 3.

Note 2: With some WebSocket clients, we've noticed that the client is not always aware of when the connection has been dropped. It can be hard for clients to discern between a network disruption and latency. Because of this, we added an explicit heartbeat subscription to Mesh that you can subscribe to. If a heartbeat isn't received after some interval (e.g., 20 seconds), the client can forcible drop the connection and re-establish a new one. This too is already taken care of under-the-hood for those using the Mesh Typescript client.

Happy database syncing!

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