| .. Licensed to the Apache Software Foundation (ASF) under one |
| or more contributor license agreements. See the NOTICE file |
| distributed with this work for additional information |
| regarding copyright ownership. The ASF licenses this file |
| to you under the Apache License, Version 2.0 (the |
| "License"); you may not use this file except in compliance |
| with the License. You may obtain a copy of the License at |
| |
| .. http://www.apache.org/licenses/LICENSE-2.0 |
| |
| .. Unless required by applicable law or agreed to in writing, |
| software distributed under the License is distributed on an |
| "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY |
| KIND, either express or implied. See the License for the |
| specific language governing permissions and limitations |
| under the License. |
| |
| Sensors |
| ======= |
| |
| Sensors are a special type of :doc:`Operator <operators>` that are designed to do exactly one thing - wait for something to occur. It can be time-based, or waiting for a file, or an external event, but all they do is wait until something happens, and then *succeed* so their downstream tasks can run. |
| |
| Because they are primarily idle, Sensors have three different modes of running so you can be a bit more efficient about using them: |
| |
| * ``poke`` (default): The Sensor takes up a worker slot for its entire runtime |
| * ``reschedule``: The Sensor takes up a worker slot only when it is checking, and sleeps for a set duration between checks |
| * ``smart sensor``: There is a single centralized version of this Sensor that batches all executions of it |
| |
| The ``poke`` and ``reschedule`` modes can be configured directly when you instantiate the sensor; generally, the trade-off between them is latency. Something that is checking every second should be in ``poke`` mode, while something that is checking every minute should be in ``reschedule`` mode. |
| |
| Smart Sensors take a bit more setup; for more information on them, see :doc:`smart-sensors`. |
| |
| Much like Operators, Airflow has a large set of pre-built Sensors you can use, both in core Airflow as well as via our *providers* system. |
