Implementation:Apache Druid ShowLog

Knowledge Sources	Apache_Druid
Domains	Web_Console, Task_Monitoring
Last Updated	2026-02-10 10:00 GMT

Overview

ShowLog is a class-based React component that fetches and displays log output from a Druid API endpoint with optional tail-following, download, copy, and raw-view capabilities.

Description

The component uses a QueryManager to fetch log data from the specified endpoint, supporting a tail offset parameter to fetch only the last portion of large log files. When tail mode is enabled, it polls the endpoint at a configurable interval (default 2500ms) and auto-scrolls the textarea to the bottom to follow new log output. The first partial line is stripped when using tail offset to avoid displaying truncated content. The component provides buttons for downloading the full log, copying to clipboard, and opening the raw log endpoint in a new tab.

Usage

Used in the Druid web console's task detail views to display indexing task logs, supervisor logs, and other process output with live tail-following for active tasks.

Code Reference

Source Location

• Repository: Apache Druid
• File: web-console/src/components/show-log/show-log.tsx
• Lines: 1-209

Signature

export interface ShowLogProps {
  endpoint: string;
  downloadFilename?: string;
  tailOffset?: number;
  tail?: boolean;
}

export interface ShowLogState {
  logState: QueryState<string>;
  tail: boolean;
}

export class ShowLog extends React.PureComponent<ShowLogProps, ShowLogState> {
  static CHECK_INTERVAL: number;
}

Import

import { ShowLog } from './components/show-log/show-log';

I/O Contract

Inputs

Name	Type	Required	Description
endpoint	string	Yes	The Druid API endpoint URL path to fetch log content from
downloadFilename	string	No	If provided, enables a download anchor linking to the log endpoint
tailOffset	number	No	The number of bytes from the end to fetch (appended as ?offset=-N to the URL)
tail	boolean	No	When true, enables the tail-following toggle and starts periodic polling

Outputs

Name	Type	Description
JSX.Element	div	A container with a tail toggle switch, action buttons, and either a Loader, special instructions, or a read-only textarea displaying log content

Usage Examples

Tailing a task log

<ShowLog
  endpoint={`/druid/indexer/v1/task/${taskId}/log`}
  downloadFilename={`task-log-${taskId}.log`}
  tailOffset={16384}
  tail
/>

Related Pages

• Environment:Apache_Druid_Web_Console_Development