What is Websocket, in plain terms?
Websocket is a communication protocol that keeps a connection open between two systems. After the initial setup, both sides can send messages to each other without repeatedly creating new requests. In practice, this can be used to stream updates (for example, quotes or market events) from a market data provider or platform to a client.
It helps to separate two ideas:
- The protocol mechanics: how messages are sent and received over an open connection.
- Market usefulness: whether the messages you receive are timely, complete, and aligned with what you need for a specific application.
The main limitation is that Websocket only addresses how you transport messages, not whether those messages represent stable, real-time, or future-proof information.
How does Websocket work, and what assumptions can break?
With Websocket, messages flow over a persistent channel. In a typical streaming setup, a client subscribes to certain data (by symbol, instrument, or topic), and the server pushes updates as they occur.
Key assumptions behind “it works well” expectations include:
- The connection stays healthy long enough for the application to run.
- Messages arrive in a usable order and frequency for your logic.
- The server actually publishes updates as you expect (for the chosen subscription and time).
- Your client can process messages fast enough to keep up.
When any of these assumptions fail, you can see outcomes such as missing updates, increased delay, backlog, or repeated reconnect attempts.
Example failure modes you can observe (without assuming real-time behavior)
Even if you do not assume live market data, you can still evaluate failure modes in a system design sense:
- Reconnection gaps: If the connection drops, the client may reconnect later. During the gap, updates may be missed.
- Backpressure and buffering: If message processing or network throughput is slower than the incoming update rate, messages can queue, increasing latency.
- Ordering and deduplication needs: Systems often need to handle duplicates (retries after reconnect) and out-of-order arrival across reconnections.
A common misconception is treating delivery over a persistent socket as synonymous with perfect timeliness or completeness. Websocket can reduce communication overhead, but it does not remove the need for gap handling, deduplication, and time alignment.
Limitations and risks: where Websocket is less useful
Websocket limitations are most visible when they interact with variable external conditions:
- Network and infrastructure volatility: Latency, packet loss, or intermittent connectivity can still affect when and how messages arrive.
- Provider/server behavior changes: Update frequency, available subscriptions, or throttling policies can differ by provider and by conditions.
- Execution vs. data timing mismatch: Even if you receive data quickly, your downstream actions (such as calculations, order handling, or system scheduling) may still lag.
- Costs and operational overhead: Persistent connections, reconnection strategies, and monitoring add complexity; complexity increases the chance of edge-case failures.
- Uncertainty about “real-time accuracy”: Historical relationships between message timing and outcomes do not guarantee that the same relationship will hold in the future.
Because these factors vary across systems and jurisdictions, you should treat Websocket as a transport mechanism and validate what you receive under your actual conditions.
How to verify Websocket limits independently
To verify limitations without relying on promises, define measurable checks for your own setup. For example:
- Track connect/disconnect events, and record how long reconnection gaps last.
- Measure end-to-end message delay from receipt to the moment your application uses the data.
- Confirm whether your system properly handles duplicates and missing messages after reconnect.
- Evaluate whether message volume during high activity causes processing backlog.
If your requirements include strict timeliness or completeness, consider whether your design includes monitoring, reconciliation, and robust handling of uncertainty. In general, the limitation of Websocket is not the protocol itself, but how assumptions about delivery, timing, and data quality are validated (or not) in the real environment.