How to Convert a Jeonse Deposit into Monthly Rent in Korea
Jeonse-to-monthly-rent conversion turns a lump-sum deposit into rent with a single annual rate. Here is the formula, a worked example, and a calculator.
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Databases
Hot-Swapping Cron Schedules with MongoDB Change Streams
Hardcoded cron means a redeploy every time a schedule changes. Store schedules in the database and have a daemon react to edits with change streams. Here is the design and its failure handling.
Backend
Load Balancing a GPU Worker Pool with Redis Keyspace Notifications and Leases
GPUs are expensive and run one heavy job at a time, so round-robin routing stalls behind busy workers. Here is a busy-aware scheduler built from Redis leases and keyspace notifications.
Backend
Lease Locks with CAS and Heartbeat for Single-Runner Jobs
A plain lock deadlocks forever when the holder dies. A lease expires. Here is how to build one with compare-and-swap acquisition and a heartbeat, and the failure modes that decide the design.
Databases
Why Cursor Pagination Beats Skip in a Metered Database
skip(N) reads and discards every document it steps over, and a per-read database charges you for all of them. Here is the arithmetic, the query that replaces it, and the tie-breaker that keeps order stable.
Databases
Deterministic ULIDs for Idempotent Upserts
When a database forbids automatic write retries, every write must be idempotent on its own. A content-derived id makes that free. Here is the derivation and the one invariant that keeps it safe.
Databases
The retryWrites=false Trap in Firestore's MongoDB Compatibility
Firestore speaks the MongoDB wire protocol, but rejects retryable writes. If your driver defaults to on, writes fail in a way that looks random. Here is why, and the fix.
Backend
Moving a Backend from Rust to Go, and Why Build Time Decided It
Rust gave us safety we rarely needed and a compile loop we fought every day. Here is the honest tradeoff, with numbers, that pushed a service to Go.