OTP

OTP

(Open Telecom Platform) is a collection of framework/lib/tools written in Erlang

Horrible error messaging

Observer

iex(1)> observer.start()

Erlang Term Storage (ETS)

In-memory store key value for elixir and erlang

>10x Faster than redis according to

  • Created and owned by individual processes(destroyed on exit), so back with GenServer and now any process can access, no bottleneck

  • Only limit is server memory.

  • Because multiple can access at the same time unlike message based agents, operations must be atomic (ft for something like counter updating)

    • Concurrent reads with serial writes is a common ETS pattern

Applications of ETS

  • persisent shared state(tzdata, )

  • ephemeral shared state(cache, rate limiter)

  • IPC

Usage

tab = :ets.new(:my_table, [:set]) #=> 8211

:ets.insert(tab, {:key1, "value1"}) #=> true

:ets.lookup(tab, :key1) #=> [key1: "value1"]

Advanced

:ets.tab2list(:rate_limiter_requests) #[[key1: "value1"]]

http://erlang.org/doc/man/disk_log.html

Disk Based ETS(DETS)

APIS are interchangeable except

  • how tables are created with named table default

  • :dets vs :ets and fewer features

  • Slower cuz disk

{:ok, table} = :dets.open_file(:disk_storage, [type: :set]) #{:ok, :disk_storage}
:dets.open_file(:file_table, [{:file, "test/test.txt"}])

Usage

:dets.insert(table, {:k, 1}) #can also use :name to access table as that is what table is
:dets.lookup(:file_table, :a) # => [a: 3]
:dets.close(:file_table) #If you don't do this, the table will be repaired the next time it is opened.
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