Implementation:Eventual Inc Daft Increment Counter

Knowledge Sources	Daft Daft Docs
Domains	Data_Engineering, Observability
Last Updated	2026-02-08 00:00 GMT

Overview

Concrete tool for incrementing custom counter metrics within UDF execution provided by the Daft library.

Description

The increment_counter function increments a named counter metric during UDF execution. It validates that the metric name is a non-empty string, the description (if provided) is a string, and all attribute keys and values are strings. If called outside a UDF execution context, a RuntimeWarning is emitted and the call is a no-op. Internally, it delegates to the Rust-backed OperatorMetrics.inc_counter method for efficient metric storage.

Usage

Import from daft.udf.metrics and call within UDF function or class method bodies to track custom counters.

Code Reference

Source Location

• Repository: Daft
• File: daft/udf/metrics.py
• Lines: L19-55

Signature

def increment_counter(
    name: str,
    amount: int = 1,
    *,
    description: str | None = None,
    attributes: Mapping[str, str] | None = None,
) -> None

Import

from daft.udf.metrics import increment_counter

I/O Contract

Inputs

Name	Type	Required	Description
name	str	Yes	The metric counter name. Must be a non-empty string.
amount	int	No	The amount to increment the counter by. Defaults to 1.
description	None	No	Optional description of the metric.
attributes	None	No	Optional key-value attribute tags for categorizing the metric.

Outputs

Name	Type	Description
return	None	No return value. Metrics are collected internally for aggregation by the execution framework.

Usage Examples

Basic Usage

import daft
from daft.udf.metrics import increment_counter

@daft.func
def process_row(value: str) -> str:
    if is_cached(value):
        increment_counter("cache_hits")
    else:
        increment_counter("cache_misses")
    return transform(value)

With Attributes

from daft.udf.metrics import increment_counter

increment_counter(
    "api_calls",
    amount=1,
    description="Number of external API calls",
    attributes={"endpoint": "/v1/predict", "status": "200"},
)

Related Pages

Implements Principle

• Principle:Eventual_Inc_Daft_UDF_Metrics

Requires Environment

• Environment:Eventual_Inc_Daft_Python_PyArrow_Core