[elixir! 0073] beam built-in memory database ETS

stay beam In the virtual machine , Processes usually communicate with each other through message passing , And messaging needs to be replicated, not shared . The message size is small , And only spread between a small number of processes , There is no performance problem . And if we need to share a lot of data between a large number of processes , So messaging is very inefficient and unnecessary .

Erlang It's been considered for a long time , stay beam Added in ETS（erlang term storage）, It allows different processes to share data directly . Let's try how it works ：

First, let's create a new one ETS surface , Choose to name it :table_a, The type is set, Similar to hash table .

:ets.new(:table_a, [:named_table, :set])

We can use :ets.info/1 Function to view the details of this table .

iex(2)> :ets.info :table_a
[
  id: #Reference<0.679153060.3873570820.49251>,
  read_concurrency: false,
  write_concurrency: false,
  compressed: false,
  memory: 307,
  owner: #PID<0.239.0>,
  heir: :none,
  name: :table_a,
  size: 0,
  node: :nonode@nohost,
  named_table: true,
  type: :set,
  keypos: 1,
  protection: :protected
]

Notice here and socket equally , There needs to be a process as owner, To bind erlang The process world and the outside world （ets,port etc. ） The relationship between , So that link and mointor Mechanisms can be extended to these external components . once owner crash,ets The watch will disappear with it .

":set" How to use types and map almost . default key yes tuple Of the 1 Elements （ from 1 Start counting ）.

Let's continue to use BonyTrace Let's test it , See if you really can share data without any messaging .

    spawn(fn ->
      BonyTrace.start(self())

      table = :ets.new(:ets_map, [:named_table, :set, :public])

      :ets.insert(table, {"key1", "value1"})

      spawn(fn ->
        [{"key1", "value1"}] = :ets.lookup(table, "key1")
      end)

      :timer.sleep(5000)
    end)

Be careful ets table Must be set to :public Can be accessed by other processes . After execution, only the timer is printed out timeout The news of . therefore ets It's really a convenient tool for data sharing between processes .

#PID<0.331.0> RECEIVED                                 +0.000000s
MESSAGE: :timeout