Implementation:Apache Druid MaxTasksButton

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

Overview

MaxTasksButton is a React component that provides a dropdown button for configuring the maximum number of tasks for MSQ query execution.

Description

The component renders a BlueprintJS Popover with a menu allowing users to set the maxNumTasks query context parameter for multi-stage queries. It offers preset options (2, 3, 4, 5, 7, 9, 11, 17, 33, 65, 129 by default), a "full cluster capacity" option when cluster capacity is known, a custom numeric input dialog for arbitrary values, and a task assignment mode selector (max vs auto). The button label dynamically displays the current setting. Options exceeding the cluster capacity are automatically filtered out. Custom label functions for task counts and cluster capacity can be provided for flexible display.

Usage

Used in the workbench view toolbar to allow users to control parallelism of MSQ task execution before running a query. Appears alongside other query configuration controls.

Code Reference

Source Location

• Repository: Apache Druid
• File: web-console/src/views/workbench-view/max-tasks-button/max-tasks-button.tsx
• Lines: 1-194

Signature

export interface MaxTasksButtonProps extends Omit<ButtonProps, 'text' | 'rightIcon'> {
  clusterCapacity: number | undefined;
  queryContext: QueryContext;
  changeQueryContext(queryContext: QueryContext): void;
  defaultQueryContext: QueryContext;
  menuHeader?: JSX.Element;
  maxTasksLabelFn?: (maxNum: number) => { text: string; label?: string };
  maxTasksOptions?: number[];
  fullClusterCapacityLabelFn?: (clusterCapacity: number) => string;
}

export const MaxTasksButton = function MaxTasksButton(
  props: MaxTasksButtonProps,
): JSX.Element;

Import

import { MaxTasksButton } from 'web-console/src/views/workbench-view/max-tasks-button/max-tasks-button';

I/O Contract

Inputs

Name	Type	Required	Description
clusterCapacity	number or undefined	No	Total number of available task slots in the cluster
queryContext	QueryContext	Yes	The current query context object containing maxNumTasks
changeQueryContext	(queryContext: QueryContext) => void	Yes	Callback to update the query context when a selection is made
defaultQueryContext	QueryContext	Yes	Default query context for deriving default task assignment
menuHeader	JSX.Element	No	Optional header element rendered at the top of the popover menu
maxTasksLabelFn	function	No	Custom label function for task count menu items
maxTasksOptions	number[]	No	Custom array of task count options (defaults to [2,3,4,5,7,9,11,17,33,65,129])
fullClusterCapacityLabelFn	function	No	Custom label function for the full cluster capacity option

Outputs

Name	Type	Description
JSX.Element	Fragment	A Popover-wrapped Button with task count menu and optional NumericInputDialog for custom values

Usage Examples

Rendering the max tasks button with cluster capacity

<MaxTasksButton
  clusterCapacity={32}
  queryContext={currentContext}
  changeQueryContext={(ctx) => setQueryContext(ctx)}
  defaultQueryContext={defaultContext}
/>

Related Pages

• Environment:Apache_Druid_Web_Console_Development