class pyspark.sql.Observation(name: Optional[str] = None)

Class to observe (named) metrics on a DataFrame.

Metrics are aggregation expressions, which are applied to the DataFrame while it is being processed by an action.

The metrics have the following guarantees:

  • It will compute the defined aggregates (metrics) on all the data that is flowing through the Dataset during the action.

  • It will report the value of the defined aggregate columns as soon as we reach the end of the action.

The metrics columns must either contain a literal (e.g. lit(42)), or should contain one or more aggregate functions (e.g. sum(a) or sum(a + b) + avg(c) - lit(1)). Expressions that contain references to the input Dataset’s columns must always be wrapped in an aggregate function.

An Observation instance collects the metrics while the first action is executed. Subsequent actions do not modify the metrics returned by Observation.get. Retrieval of the metric via Observation.get blocks until the first action has finished and metrics become available.


This class does not support streaming datasets.


>>> from pyspark.sql.functions import col, count, lit, max
>>> from pyspark.sql import Observation
>>> df = spark.createDataFrame([["Alice", 2], ["Bob", 5]], ["name", "age"])
>>> observation = Observation("my metrics")
>>> observed_df = df.observe(observation, count(lit(1)).alias("count"), max(col("age")))
>>> observed_df.count()
>>> observation.get
{'count': 2, 'max(age)': 5}



Get the observed metrics.