Hyper.Img.Db.Gc (Hyper v0.1.0)

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Cluster-singleton garbage collector that reconciles the blobs table against the shared medium: a :present blob whose backing file is gone is a stale row and is pruned. Runs continuously, one keyset page at a time.

Deletes are irreversible, so a blob is pruned only when all of these agree it is really gone:

  1. Errno discrimination - Hyper.Node.Layer.Repo.find_layer/1 reports :enoent only for a true absence; any other I/O error (NFS ESTALE/EIO, a vanished mount) is treated as :unknown and never pruned.
  2. Mount re-check - test_system/0 is re-checked after a page's probes and before its deletes, so a mount that drops mid-page can't trigger a mass delete.
  3. Grace period - rows younger than grace_period are never deleted, so a blob mid-publish (row present, file not finished) is safe.

The DELETE is also guarded by NOT EXISTS against image_layers, so it can never violate the FK. A missing-file blob still referenced by an image is a dangling reference (data loss the GC can't fix) - left in place and reported, never deleted.

Publish contract: write a layer's file to the medium before inserting its blobs row (ideally write-temp then atomic rename); the grace period is insurance, not a substitute.

The delete step itself lives in Hyper.Img.Db.Gc.Prune.

Summary

Types

t()

Functions

child_spec(init_arg)

Returns a specification to start this module under a supervisor.

start_link(opts \\ [])
status()

Local role + last completed sweep, for introspection on this node.

Types

t()

@type t() :: %Hyper.Img.Db.Gc{
  config: Hyper.Cfg.Gc.t(),
  last_sweep: Hyper.Img.Db.Gc.Sweep.State.t() | nil,
  role: :active | :standby,
  sweep: Hyper.Img.Db.Gc.Sweep.State.t() | nil
}

Functions

child_spec(init_arg)

Returns a specification to start this module under a supervisor.

See Supervisor.

start_link(opts \\ [])

@spec start_link(keyword()) :: GenServer.on_start()

status()

@spec status() :: %{
  role: :active | :standby,
  last_sweep: Hyper.Img.Db.Gc.Sweep.State.t() | nil
}

Local role + last completed sweep, for introspection on this node.