Code Modules and Organization

Before proceeding to contributing changes to Pinot, review the contents of this section.

External Dependencies

Pinot depends on a number of external projects, the most notable ones are:

  • Apache Zookeeper
  • Apache Helix
  • Apache Kafka
  • Apache Thrift
  • Netty
  • Google Guava
  • Yammer

Helix is used for ClusterManagement, and Pinot code is tightly integrated with Helix and Zookeeper interfaces.

Kafka is the default realtime stream provider, but can be replaced with others. See customizations section for more info.

Thrift is used for message exchange between broker and server components, with Netty providing the server functionality for processing messages in a non-blocking fashion.

Guava is used for number of auxiliary components such as Caches and RateLimiters. Yammer metrics is used to register and expose metrics from Pinot components.

In addition, Pinot relies on several key external libraries for some of its core functionality: Roaring Bitmaps: Pinot’s inverted indices are built using this library. t-Digest: Pinot’s digest based percentile calculations are based on this library.

Pinot Modules

Pinot is a multi-module project, with each module providing specific functionality that helps us to build services from a combination of modules. This helps keep clean interface contracts between different modules as well as reduce the overall executable size for individually deployable component.

Each module has a src/main/java folder where the code resides and src/test/java where the unit tests corresponding to the module’s code reside.

Foundational modules

The following figure provides a high-level overview of the foundational Pinot modules.

_images/PinotFoundation.png

pinot-common

pinot-common provides classes common to Pinot components. Some key classes you will find here are:

  • config: Definitions for various elements of Pinot’s table config.
  • metrics: Definitions for base metrics provided by Controller, Broker and Server.
  • metadata: Definitions of metadata stored in Zookeeper.
  • pql.parsers: Code to compile PQL strings into corresponding AbstractSyntaxTrees (AST).
  • request: Autogenerated thrift classes representing various parts of PQL requests.
  • response: Definitions of response format returned by the Broker.
  • filesystem provides abstractions for working with segments on local or remote filesystems. This module

allows for users to plugin filesystems specific to their usecase. Extensions to the base PinotFS should ideally be housed in their specific modules so as not pull in unnecessary dependencies for all users.

pinot-transport

pinot-transport module provides classes required to handle scatter-gather on Pinot Broker and netty wrapper classes used by Server to handle connections from Broker.

pinot-core

pinot-core modules provides the core functionality of Pinot, specifically for handling segments, various index structures, query execution - filters, transformations, aggregations etc and support for realtime segments.

pinot-server

pinot-server provides server specific functionality including server startup and REST APIs exposed by the server.

_images/PinotServer.png

pinot-controller

pinot-server houses all the controller specific functionality, including many cluster administration APIs, segment upload (for both offline and realtime), segment assignment, retention strategies etc.

_images/PinotController.png

pinot-broker

pinot-broker provides broker functionality that includes wiring the broker startup sequence, building broker routing tables, PQL request handling.

_images/PinotBroker.png

pinot-minion

pinot-minion provides functionality for running auxiliary/periodic tasks on a Pinot Cluster such as purging records for compliance with regulations like GDPR.

pinot-hadoop

pinot-hadoop provides classes for segment generation jobs using Hadoop infrastructure.

_images/PinotMinionHadoop.png

Auxiliary modules

In addition to the core modules described above, Pinot code provides the following modules:

  • pinot-tools: This module is a collection of many tools useful for setting up Pinot cluster, creating/updating segments.
    It also houses the Pinot quick start guide code.
  • pinot-perf: This module has a collection of benchmark test code used to evaluate design options.
  • pinot-client-api: This module houses the Java client API. See Executing queries via Java Client API for more info.
  • pinot-integration-tests: This module holds integration tests that test functionality across multiple classes or components.

These tests typically do not rely on mocking and provide more end to end coverage for code.

Extension modules

pinot-hadoop-filesystem and pinot-azure-filesystem are module added to support extensions to Pinot filesystem. The functionality is broken down into modules of their own to avoid polluting the common modules with additional large libraries. These libraries bring in transitive dependencies of their own that can cause classpath conflicts at runtime. We would like to avoid this for the common usage of Pinot as much as possible.