Implementation:Apache Druid SampleForParser

Knowledge Sources	Apache Druid Druid Input Formats
Domains	Data_Ingestion, Data_Parsing
Last Updated	2026-02-10 00:00 GMT

Overview

Concrete sampler API client function for applying input format parsing to raw sample data.

Description

The sampleForParser function sends a sampling request to the Druid Sampler API with the user-configured inputFormat applied. It uses the applyCache() utility to leverage previously cached sample data from the connection step, avoiding redundant reads from the external source. For reindexing mode, it uses a special detection timestamp spec to properly handle existing Druid columns.

Usage

Call this function after source connection succeeds and the user has selected or confirmed an input format. The function returns parsed data that shows column names and typed values for user verification.

Code Reference

Source Location

Repository: Apache Druid
File: web-console/src/utils/sampler.ts
Lines: L351-L384

Signature

export async function sampleForParser(
  spec: Partial<IngestionSpec>,
  sampleStrategy: SampleStrategy,
): Promise<SampleResponse>

Import

import { sampleForParser } from '../utils/sampler';

I/O Contract

Inputs

Name	Type	Required	Description
spec	Partial<IngestionSpec>	Yes	Ingestion spec with ioConfig.inputFormat configured (json, csv, tsv, parquet, etc.)
sampleStrategy	SampleStrategy	Yes	Sampling strategy (typically reuses cached data)

Outputs

Name	Type	Description
data	SampleEntry[]	Array of parsed rows with column names and values
cacheKey	string or undefined	Updated cache key for subsequent sampler calls

Usage Examples

Parsing JSON Data

import { sampleForParser } from '../utils/sampler';

const spec = {
  type: 'index_parallel',
  spec: {
    ioConfig: {
      inputSource: { type: 's3', uris: ['s3://bucket/data.json'] },
      inputFormat: { type: 'json' },
    },
  },
};

const result = await sampleForParser(spec, 'start');
// result.data[0].parsed = { timestamp: '2024-01-01', user: 'alice', count: 42 }

Parsing CSV with Header

const csvSpec = {
  type: 'index_parallel',
  spec: {
    ioConfig: {
      inputSource: { type: 'http', uris: ['https://example.com/data.csv'] },
      inputFormat: {
        type: 'csv',
        findColumnsFromHeader: true,
        skipHeaderRows: 0,
      },
    },
  },
};

const result = await sampleForParser(csvSpec, 'start');

Related Pages

Implements Principle

Principle:Apache_Druid_Data_Parsing

Requires Environment

Uses Heuristic

Heuristic:Apache_Druid_Sampler_Limitations_And_Workarounds

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Implementation

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