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

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.