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What is shelf?

shelf combines ETS (fast, in-memory) with DETS (persistent, on-disk) to give you microsecond reads with durable storage. It implements the classic Erlang persistence pattern, wrapped in a type-safe Gleam API.

How it works

Section titled “How it works”
block-beta
  columns 2
  App["Your Application"]:2
  Shelf["shelf (this library)"]:2
  ETS["ETS (memory)\n• μs reads\n• μs writes\n• in-process"]
  DETS["DETS (disk)\n• persistence\n• survives restarts"]

Reads always go to ETS — consistent microsecond latency regardless of table size.

Writes go to ETS immediately. Persistence to DETS depends on the write mode.

Why shelf?

Section titled “Why shelf?”

If you only need ETS or DETS individually, check out these standalone wrappers:

  • bravo — Type-safe ETS wrapper for Gleam
  • slate — Type-safe DETS wrapper for Gleam

shelf coordinates both together, using Erlang's native ets:to_dets/2 and ets:from_dets/2 for efficient bulk transfers.

Key features

Section titled “Key features”
  • Microsecond reads: All reads go through ETS for consistent performance
  • Write modes: Choose between WriteBack (batched) or WriteThrough (immediate persistence)
  • Three table types: set, bag, duplicate_bag
  • Atomic counters: Increment integer values atomically in ETS
  • Safe resource management: with_table ensures tables are always closed
  • Zero external dependencies: Built entirely on OTP's ETS and DETS