https://blog.yusukeikoma.com/tags/distributed-systems/Recent content in distributed-systems on Ikoma's BlogHugoen-usSat, 19 Sep 2026 21:10:16 +0900https://blog.yusukeikoma.com/posts/push-notifications-are-hints-apns-stores-one/Sat, 19 Sep 2026 21:10:16 +0900https://blog.yusukeikoma.com/posts/push-notifications-are-hints-apns-stores-one/Apple and Google both document what happens to a push when the device is offline, the app is killed or the sender is too chatty: messages are replaced, dropped, reordered or delayed. A table of those documented failure modes, and a small simulation showing that a client which pulls from a cursor converges where a client which applies push payloads does not.https://blog.yusukeikoma.com/posts/resumable-streams-cursors-last-event-id-snapshots/Fri, 04 Sep 2026 19:26:37 +0900https://blog.yusukeikoma.com/posts/resumable-streams-cursors-last-event-id-snapshots/How a client catches up after a reconnect without losing state, without duplicates, and without re-reading history. Built in steps (versions 0 to 4), from “read everything again” to a bounded log with a snapshot fallback, with what a real browser’s EventSource does on reconnect and on a non-200 response, a snapshot-ordering bug, and a decision tree.https://blog.yusukeikoma.com/posts/exactly-once-delivery-idempotency-and-backoff/Fri, 28 Aug 2026 10:07:45 +0900https://blog.yusukeikoma.com/posts/exactly-once-delivery-idempotency-and-backoff/When a request times out, the client cannot tell whether the request or only its acknowledgement was lost. This is why exactly-once delivery cannot be built, and why effectively-once processing is at-least-once delivery plus a receiver that deduplicates. A runnable experiment with a flaky network, the bug that still duplicates 89 of 200 requests, an atomic dedupe store, and a jitter simulation.https://blog.yusukeikoma.com/posts/level-triggered-invalidation/Tue, 25 Aug 2026 17:33:01 +0900https://blog.yusukeikoma.com/posts/level-triggered-invalidation/epoll’s edge-triggered mode stalls after a partial read; level-triggered mode cannot. The same distinction decides whether a realtime client survives lost, duplicated and reordered events. A reproducible epoll experiment, a five-way simulation on a lossy channel, and a 40-line invalidator that handles the race everyone misses: an event that arrives while the refetch is running.https://blog.yusukeikoma.com/posts/live-document-and-saved-copy/Thu, 13 Aug 2026 10:14:09 +0900https://blog.yusukeikoma.com/posts/live-document-and-saved-copy/Designing collaborative document editing with conflict-free synchronization, saved snapshots, and safeguards against overwriting content before initial sync.https://blog.yusukeikoma.com/posts/one-open-admission/Wed, 12 Aug 2026 10:27:31 +0900https://blog.yusukeikoma.com/posts/one-open-admission/Controlling distributed task starts with one unfinished admission per workspace surface, a fixed destination, and idempotent retries during machine outages.