api-plugin-helper-storage.md

Plugin Helper: Storage

The storage plugin helper manages the plugin's internal states.

Here is an example:

require 'fluent/plugin/input'

module Fluent::Plugin
  class ExampleInput < Input
    Fluent::Plugin.register_input('awesome_example', self)

    # 1. Load storage helper
    helpers :storage, :thread

    DEFAULT_STORAGE_TYPE = 'local'

    # Omit `shutdown` and other plugin APIs

    def initialize
      super

      @storage = nil
    end

    def configure(conf)
      super

      # 2. Create storage with unique name
      config = conf.elements(name: 'storage').first
      @storage = storage_create(usage: 'awesome_index', conf: config, default_type: DEFAULT_STORAGE_TYPE)
    end

    def start
      super

      # 3. Call storage plugin helpers get/put methods
      @storage.put(:awesome_index, 0) unless @storage.get(:awesome_index)
      thread_create(:awesome_input_runner, &method(:run))
    end

    def run
      while thread_current_running?
        current_time = Time.now.to_i
        break unless (thread_current_running? && Time.now.to_i <= current_time)
        router.emit('awesome', Fluent::Engine.now, generate)
        sleep 0.1
      end
    end

    def generate
      # 4. Update storage plugin helper's storing value
      @storage.update(:awesome_index) { |v| v + 1 }
    end
  end
end

The created storage is managed by the plugin helper. No need of storage shutdown code in plugin's shutdown. It shutdowns the created storages automatically.

For more details, see Storage section.

Methods

storage_create(usage: '', type: nil, conf: nil, default_type: nil)

This method executes storage with the given parameters and routine.

• usage: unique string value (default: '')
• type: storage plugin type (default: nil)
• conf: storage plugin configuration (default: nil)
• default_conf: storage plugin default configuration (default: nil)

Storage Plugin Helper Instance Types

Instance Type	Attributes

Raw | persistent && persistent_always? || otherwise | Persistent Wrapper | persistent | Synchronized Wrapper | !synchronized? |

Raw

Storage plugins will handle as-is.

Persistent Wrapper

This wrapper makes the handled storage plugin operate values persistently.

Synchronized Wrapper

This wrapper makes handled storage plugin operate values synchronically.

Common Methods

Storage plugin helper encapsulates storage plugin implementation. Normally, the following methods will be called by the owner plugin through this plugin helper:

load

This method loads persistently stored value.

save

This method saves value persistently.

get(key)

• key: symbol value.

This method obtains stored value by key.

fetch(key, defval)

• key: symbol value.
• defval: default value.

This method obtains the stored value by key. If missing, it returns the default value.

put(key, value)

• key: symbol value.
• value: store value.

This method updates the stored value by key.

delete(key)

• key: symbol value.

This method deletes the stored value by key.

update(key, &block)

• key: symbol value.
• &block: a Proc object.

This method updates the stored value using a Proc object.

Plugins using storage

• in_sample
• in_windows_eventlog

If this article is incorrect or outdated, or omits critical information, please let us know. Fluentd is an open-source project under Cloud Native Computing Foundation (CNCF). All components are available under the Apache 2 License.