Slap.SlateDB.Reader (slap_slatedb v0.2.0)

Read-only access to a database, alongside its writer.

A reader does not fence the writer, so any number of readers can follow one database, in this VM or elsewhere. It picks up the writer's changes by polling the manifest and replaying the WAL.

{:ok, reader} = Slap.SlateDB.Reader.open("my-db", store: store)
{:ok, value} = Slap.SlateDB.Reader.get(reader, "key")
reader |> Slap.SlateDB.Reader.scan(prefix: "user:") |> Enum.take(10)
:ok = Slap.SlateDB.Reader.close(reader)

A reader sees writes once they are durable (in the WAL in object storage), within manifest_poll_interval. It does not see writes that are still only in the writer's memory.

Summary

Types

t()

Functions

close(reader, opts \\ [])

Closes the reader. It waits for calls in flight; later calls get a :closed error. Closing twice is allowed. A :managed reader's checkpoint is left to expire.

durable_seq(reader)

Returns the highest durable sequence number the reader has seen.

get(reader, key, opts \\ [])

Reads key. Takes the options of Slap.SlateDB.get/3.

get_key_value(reader, key, opts \\ [])

Reads key with its metadata, like Slap.SlateDB.get_key_value/3.

iterator(reader, opts \\ [])

Opens a Slap.SlateDB.Iterator. Takes the options of Slap.SlateDB.iterator/2.

open(path, opts)

Opens a reader for the database at path.

scan(reader, opts \\ [])

Scans rows. Takes the options of Slap.SlateDB.scan/2.

Types

t()

@opaque t()

Functions

close(reader, opts \\ [])

@spec close(t(), keyword()) :: :ok | {:error, Slap.SlateDB.Error.t()}

Closes the reader. It waits for calls in flight; later calls get a :closed error. Closing twice is allowed. A :managed reader's checkpoint is left to expire.

durable_seq(reader)

@spec durable_seq(t()) :: non_neg_integer()

Returns the highest durable sequence number the reader has seen.

get(reader, key, opts \\ [])

@spec get(t(), binary(), keyword()) ::
  {:ok, binary() | nil} | {:error, Slap.SlateDB.Error.t()}

Reads key. Takes the options of Slap.SlateDB.get/3.

get_key_value(reader, key, opts \\ [])

@spec get_key_value(t(), binary(), keyword()) ::
  {:ok, Slap.SlateDB.key_value() | nil} | {:error, Slap.SlateDB.Error.t()}

Reads key with its metadata, like Slap.SlateDB.get_key_value/3.

iterator(reader, opts \\ [])

@spec iterator(t(), keyword()) ::
  {:ok, Slap.SlateDB.Iterator.t()} | {:error, Slap.SlateDB.Error.t()}

Opens a Slap.SlateDB.Iterator. Takes the options of Slap.SlateDB.iterator/2.

open(path, opts)

@spec open(String.t(), keyword()) :: {:ok, t()} | {:error, Slap.SlateDB.Error.t()}

Opens a reader for the database at path.

Options

:store - required, as for Slap.SlateDB.open/2.
:mode - how the reader tracks the database:
- :managed (default) - the reader keeps its own checkpoint, refreshed as it follows the writer, so garbage collection cannot delete files it is reading.
- :latest - no checkpoint and no writes to the store. Reads can fail if garbage collection deletes a file the reader still uses.
:checkpoint - a checkpoint id (from Slap.SlateDB.create_checkpoint/2). The reader stays at that checkpoint instead of following the writer.
:settings - a map of reader options, merged over SlateDB's defaults: manifest_poll_interval (default 10 s), checkpoint_lifetime (10 min), max_memtable_bytes, skip_wal_replay, object_store_cache_options and so on. Give the two durations in milliseconds or as a string such as "100ms", "10s", "5m" or "1h".
:cache - as for Slap.SlateDB.open/2.
:merge_operator - the database's merge operator, if it has one.
:timeout - see Slap.SlateDB.

scan(reader, opts \\ [])

@spec scan(t(), keyword()) :: Enumerable.t()

Scans rows. Takes the options of Slap.SlateDB.scan/2.