Run a pipeline¶
Runners¶
Runners are the execution mechanisms used to run pipelines. They all inherit from AbstractRunner.
SequentialRunner¶
Use SequentialRunner to execute pipeline nodes one-by-one based on their dependencies.
We recommend using SequentialRunner in cases where:
the pipeline has limited branching
the pipeline is fast
the resource-consuming steps require most of a scarce resource (e.g., significant RAM, disk memory or CPU)
Kedro uses SequentialRunner by default, so to execute the pipeline sequentially:
kedro run
You can also explicitly use SequentialRunner as follows:
kedro run --runner=SequentialRunner
ParallelRunner¶
Multiprocessing¶
You can alternatively run the nodes within the pipeline concurrently, using a ParallelRunner as follows:
kedro run --runner=ParallelRunner
Multithreading¶
While ParallelRunner uses multiprocessing, you can also run the pipeline with multithreading for concurrent execution by specifying ThreadRunner as follows:
kedro run --runner=ThreadRunner
Note
SparkDataset doesn’t work correctly with ParallelRunner. To add concurrency to the pipeline with SparkDataset, you must use ThreadRunner.
For more information on how to maximise concurrency when using Kedro with PySpark, read our guide on how to build a Kedro pipeline with PySpark.
Custom runners¶
If the built-in Kedro runners do not meet your requirements, you can also define your own runner within your project. For example, you may want to add a dry runner, which lists which nodes would be run without executing them:
Click to expand
# in src/<package_name>/runner.py
from typing import Any, Dict
from kedro.io import AbstractDataset, DataCatalog, MemoryDataset
from kedro.pipeline import Pipeline
from kedro.runner.runner import AbstractRunner
from pluggy import PluginManager
class DryRunner(AbstractRunner):
"""``DryRunner`` is an ``AbstractRunner`` implementation. It can be used to list which
nodes would be run without actually executing anything. It also checks if all the
necessary data exists.
"""
def __init__(self, is_async: bool = False, extra_dataset_patterns: Dict[str, Dict[str, Any]] = None):
"""Instantiates the runner class.
Args:
is_async: If True, the node inputs and outputs are loaded and saved
asynchronously with threads. Defaults to False.
extra_dataset_patterns: Extra dataset factory patterns to be added to the DataCatalog
during the run. This is used to set the default datasets.
"""
default_dataset_pattern = {"{default}": {"type": "MemoryDataset"}}
self._extra_dataset_patterns = extra_dataset_patterns or default_dataset_pattern
super().__init__(is_async=is_async, extra_dataset_patterns=self._extra_dataset_patterns)
def _run(
self,
pipeline: Pipeline,
catalog: DataCatalog,
hook_manager: PluginManager = None,
session_id: str = None,
) -> None:
"""The method implementing dry pipeline running.
Example logs output using this implementation:
kedro.runner.dry_runner - INFO - Actual run would execute 3 nodes:
node3: identity([A]) -> [B]
node2: identity([C]) -> [D]
node1: identity([D]) -> [E]
Args:
pipeline: The ``Pipeline`` to run.
catalog: The ``DataCatalog`` from which to fetch data.
hook_manager: The ``PluginManager`` to activate hooks.
session_id: The id of the session.
"""
nodes = pipeline.nodes
self._logger.info(
"Actual run would execute %d nodes:\n%s",
len(nodes),
pipeline.describe(),
)
self._logger.info("Checking inputs...")
input_names = pipeline.inputs()
missing_inputs = [
input_name
for input_name in input_names
if not catalog._get_dataset(input_name).exists()
]
if missing_inputs:
raise KeyError(f"Datasets {missing_inputs} not found.")
And use it with kedro run through the --runner flag:
$ kedro run --runner=<package_name>.runner.DryRunner
Load and save asynchronously¶
Note
ThreadRunner doesn’t support asynchronous load-input or save-output operations.
When processing a node, both SequentialRunner and ParallelRunner perform the following steps in order:
Load data based on node input(s)
Execute node function with the input(s)
Save the output(s)
If a node has multiple inputs or outputs (e.g., node(func, ["a", "b", "c"], ["d", "e", "f"])), you can reduce load and save time by using asynchronous mode. You can enable it by passing an --async flag to the run command as follows:
$ kedro run --async
...
2020-03-24 09:20:01,482 - kedro.runner.sequential_runner - INFO - Asynchronous mode is enabled for loading and saving data
...
Note
All the datasets used in the run have to be thread-safe in order for asynchronous loading/saving to work properly.
Run a pipeline by name¶
To run the pipeline by its name, you need to add your new pipeline to the register_pipelines() function in src/<package_name>/pipeline_registry.py:
Click to expand
def register_pipelines():
"""Register the project's pipelines.
Returns:
A mapping from pipeline names to ``Pipeline`` objects.
"""
pipelines = find_pipelines()
pipelines["__default__"] = sum(pipelines.values())
my_pipeline = pipeline(
[
# your definition goes here
]
)
pipelines["my_pipeline"] = my_pipeline
return pipelines
Then, from the command line, execute the following:
kedro run --pipeline=my_pipeline
Note
If you specify kedro run without the --pipeline option, it runs the __default__ pipeline from the dictionary returned by register_pipelines().
Further information about kedro run can be found in the Kedro CLI documentation.
Run pipelines with IO¶
The above definition of pipelines only applies for non-stateful or “pure” pipelines that do not interact with the outside world. In practice, we would like to interact with APIs, databases, files and other sources of data. By combining IO and pipelines, we can tackle these more complex use cases.
By using DataCatalog from the IO module we are still able to write pure functions that work with our data and outsource file saving and loading to DataCatalog.
Through DataCatalog, we can control where inputs are loaded from, where intermediate variables get persisted and ultimately the location to which output variables are written.
In a simple example, we define a MemoryDataset called xs to store our inputs, save our input list [1, 2, 3] into xs, then instantiate SequentialRunner and call its run method with the pipeline and data catalog instances:
Click to expand
io = DataCatalog(dict(xs=MemoryDataset()))
io.list()
Output:
Out[10]: ['xs']
io.save("xs", [1, 2, 3])
SequentialRunner().run(pipeline, catalog=io)
Output:
Out[11]: {'v': 0.666666666666667}
Configure kedro run arguments¶
The Kedro CLI documentation lists the available CLI options for kedro run. You can alternatively supply a configuration file that contains the arguments to kedro run.
Here is an example file named config.yml, but you can choose any name for the file:
$ kedro run --config=config.yml
where config.yml is formatted as below (for example):
run:
tags: tag1, tag2, tag3
pipeline: pipeline1
runner: ParallelRunner
node_names: node1, node2
env: env1
The syntax for the options is different when you’re using the CLI compared to the configuration file. In the CLI you use dashes, for example for kedro run --from-nodes=..., but you have to use an underscore in the configuration file:
run:
from_nodes: ...
This is because the configuration file gets parsed by Click, a Python package to handle command line interfaces. Click passes the options defined in the configuration file to a Python function. The option names need to match the argument names in that function.
Variable names and arguments in Python may only contain alpha-numeric characters and underscores, so it’s not possible to have a dash in the option names when using the configuration file.
Note
If you provide both a configuration file and a CLI option that clashes with the configuration file, the CLI option will take precedence.