Ring Buffer

A ring buffer is a fixed-size memory structure connected end-to-end, using two pointers to track the write and read positions; when the write pointer catches up to the read pointer, new data directly overwrites the oldest data without any memory allocation or data movement.

In a ring buffer, if the implementer does not additionally record the number of overflows or set a flag, the caller has no way at all to perceive from the outside that data has been lost.

A ring buffer is a fixed-size data structure that uses write and read pointers moving cyclically over a preallocated array; when the write pointer catches up with the read pointer, new data overwrites the oldest data or the new data is simply discarded.

The advantages of a ring buffer are constant memory usage and O(1) operation time complexity, making it suitable for temporary storage of streaming data.

For high-frequency market data streams, the ring buffer brings three benefits: zero allocation (avoiding garbage collection pauses), O(1) enqueue and dequeue (predictable latency), and built-in backpressure semantics (overwriting unconsumed old data).

Lumen OS adopts a ring buffer plus RAF loop pattern: incoming WebSocket packets are pushed into an in-memory queue with no React overhead; a decoupled requestAnimationFrame loop polls the buffer and draws updates directly to the DOM or Canvas, ensuring the browser renders only at the monitor's refresh rate.

The "overwrite oldest" default policy of a ring buffer implicitly assumes that "chronological order equals order of importance"; when the input duplication rate is extremely high, capacity is quickly filled by redundant entries, and truly rare samples get pushed out.

The fix the author adopted is: keep the ring buffer and add a fingerprint mechanism—compute a fingerprint for each payload (a composite hash of the body hash plus selected headers), maintain a "seen fingerprints" set, and when full, prioritize evicting entries with duplicate fingerprints, only touching unique events when there are no duplicates to evict.

Lazy rotation defers the rotation operation until a read or write occurs, relying on index modulo to locate slots automatically, requiring no timers at all, at the cost of being unable to proactively detect slot expiry, so validity must be judged together with timestamps.

The author used a ring buffer (an integer array of length 30, one slot per day, indexed by floor(now/86400) % 30) to add a time dimension to each link, without introducing Prometheus or a time-series database.

For a lightweight statistics interface for Agents, using a ring buffer whose length is the number of days in the window plus a floor(now/86400) % 30 index mapping is almost the lowest-cost approach to providing time-dimension information, requiring no additional infrastructure or background rotation process.

A store with a capacity limit but no overflow signal is indistinguishable in behavior from data loss at the source.

The webhook catcher built by the developer specified "store at most 100 events" and was implemented with a ring buffer, causing the 101st through 112th events to be silently lost when the Stripe test suite sent 112 webhooks in a burst.