# Yardswitch

### What it is

Yardswitch is a low-latency multiplexer for Solana data. It maintains hot connections to a cluster of backend validator nodes, deduplicates the combined stream on a first-come, first-served basis, and re-serves the result to your application over a single Yellowstone gRPC subscription.

Whichever backend node emits a given slot, account, transaction, or block first wins, so a Yardswitch subscription is consistently faster than any single node it sits in front of. A slow or temporarily unreachable upstream cannot delay your stream — the next node in the cluster has already delivered the same message.

### Key facts

* **50–100 µs of added overhead per message**, depending on subscription type. Measured end-to-end between the first backend node to emit a message and your client receiving it.
* **216,000-slot rolling replay window** (\~24 hours at mainnet slot times). Reconnect with `from_slot` set and Yardswitch streams the historical window from disk, then transitions seamlessly to live.
* **Full Yellowstone gRPC compatibility.** Yardswitch speaks the unmodified `geyser.proto` schema. Existing Yellowstone client libraries work as-is — point them at a Yardswitch endpoint and ship.

### Replay details

`from_slot` replay covers **slots, accounts, transactions, entries, and blocks\_meta**. Intra-slot account writes are preserved: if a program wrote to the same account multiple times in a single slot, every write\_version is delivered in order, so replayed state matches what a live subscriber would have seen.

The reconstructed `blocks` subscription is **live-only**. A `subscribe_blocks` request with `from_slot` set is rejected with `InvalidArgument: blocks are not possible to replay`. To get block-level data for the historical window, either:

* Subscribe to `blocks_meta` + `transactions` + `entries` (all replay) and join client-side on `slot`, or
* Subscribe to `blocks` without `from_slot` for the live tail only.

### Compatibility

Any Yellowstone gRPC client works without modification:

* `yellowstone-grpc-client` (Rust)
* `@triton-one/yellowstone-grpc` (Node / TypeScript)
* `yellowstone-grpc-python`
* `yellowstone-grpc-go`

The only Yardswitch-specific changes to existing code are the endpoint URL and the `x-token` header. The full `SubscribeRequest` schema — filters, commitment levels, account-data slicing — behaves exactly as documented in the Yellowstone reference.

```rust
let mut client = GeyserGrpcClient::build_from_shared(YARDSWITCH_ENDPOINT)?
    .x_token(Some(YARDSWITCH_TOKEN))?
    .connect()
    .await?;
// Standard Yellowstone gRPC usage from here.
```


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