Scalable microtransactions for query fees based on Connext's Vector state channels framework. It consists of multiple layers, with each layer building on top of the one below.
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Receipt — An aggregation of off-chain query fee transactions between a client and indexer that were made when querying a specific subgraph deployment.
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Transfer — Aggregates receipts between a client and indexer for a specific subgraph deployment. Transfers are created to collateralize the query fee transactions included in the receipts, and are executed (Connext: "resolved") when an indexer decides to collect the corresponding receipts. Usually, this happens when the indexer closes an allocation they created against the same subgraph deployment. When a transfer is resolved, the balances of the two participants in the state channel are updated: the balance of the client is decreased, the balance of the indexer increased. This is taking place off-chain.
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State Channel — A persistent relationship established between client and router or router and indexer.
Scalar involves three participants:
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Client — Sends queries to indexers. Each query comes with updated receipt data that includes the latest query fees.
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Indexer — Receives queries with receipt data from clients and stores copies of these receipts in its database. When it closes subgraph allocations, it resolves transfers for the allocation. This updates their balance in the state channel. Once all transfers are resolved, the indexer withdraws this amount from the state channel into staking contract, where the query fees are ultimately distributed via a rebate pool.
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Router — A component that acts as a bridge between client and indexer when it comes to managing and collateralizing state channels and transfers. Future plans include transforming this into a network of routers.
A state channel is always created between a client and router or indexer and router. There are no direct state channels between clients and indexers.
Transfers are created between a client and an indexer. However, for every transfer A, there really exist two transfers A' (in the client <> router state channel) and A'' (in the router <> indexer state channel). Whenever a transfer is resolved, both the client <> router state channel balances and the router <> indexer state channel balances are updated in the same way.
Let's say the state channel balances are as follows:
- Client <> Router channel: client = 10, router = 0
- Router <> Indexer channel: router = 20, indexer = 0
When a transfer with two receipts (5 GRT and 1 GRT, total of 6 GRT) is resolved, the state channel balances are updated to the following values:
- Client <> Router channel: client = 4, router = 6
- Router <> Indexer channel: router = 14, indexer = 6
The introduction of Scalar adds a new component, a Vector node, to the indexer infrastructure. This component manages the indexer’s state channel and is used by Indexer Service and Indexer Agent to look up transfers, resolve transfers and withdraw query fees through the staking contract.
Overview of the changes:
- The
/channel-messages-inboxendpoint of Indexer Service is removed. - A new Vector node component is introduced.
- Indexer Service uses port 8000 of the Vector node to look up transfers.
- Indexer Agent uses port 8000 of the Vector node to:
- Look up transfers
- Resolve transfers
- Withdraw query fees through the staking contract
- Subscribe to transfer events
Vector node needs its own Postgres database to keep its data separate from indexer data such as indexing rules or cost models.