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mariaex

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Pure elixir database driver for MariaDB / MySQL.

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mariaex lib mariaex lru_cache.ex
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lib/mariaex/lru_cache.ex 

defmodule Mariaex.LruCache do

  @moduledoc """

  Implements LRU cache for queries.

  """

  import :os, only: [timestamp: 0]



  def new(size) do

    {size, :ets.new(:cache, [:public])}

  end



  def lookup({_, cache}, statement) do

    case :ets.lookup(cache, statement) do

      [{_, _, info}] -> info

      _ -> nil

    end

  end



  def delete({_, cache}, statement, cleanup) do

    case :ets.lookup(cache, statement) do

      [{_, _, info}] ->

        :ets.delete(cache, statement)

        cleanup.(statement, info)

      _ ->

        nil

    end

  end



  def insert({size, cache}, statement, data, cleanup) do

    if :ets.info(cache, :size) > size, do: remove_oldest(cache, cleanup)

    :ets.insert(cache, {statement, timestamp, data})

  end



  def update({_, cache}, statement, data) do

    :ets.insert(cache, {statement, timestamp, data})

  end



  defp remove_oldest(cache, cleanup) do

    {statement, _, data} = :ets.foldl(fn({statement, timestamp, data}, nil) ->

                                          {statement, timestamp, data}

                                        ({_, timestamp, _} = actual, {_, acc_timestamp, _} = acc) ->

                                          if timestamp < acc_timestamp do actual else acc end

                                      end, nil, cache)

    cleanup.(statement, data)

    :ets.delete(cache, statement)

  end

end