How Query Engines Work

This is the companion repository for the book How Query Engines Work and contains source code for a simple in-memory query engine implemented in Kotlin.

The query engine is designed to be easy to learn and hack on rather than being optimized for performance, scalability, or robustness.

The query engine contains the following components:

• DataFrame API
• SQL Parser
• SQL Query Planner
• Logical Plan
• Query Optimizer
• Physical Plan
• Server
• JDBC Driver

The following operators are supported:

• Table Scan (Parquet and CSV)
• Projection
• Filter
• Hash Aggregate

The following expressions are supported:

• Literals
• Attributes
• Simple Aggregates (Min, Max, Sum)
• Cast
• Boolean expressions (AND, OR, NOT)
• Simple math expressions (+, -, *, /)

Installing Locally

Install the Google Protocol Buffer compiler

The gradle build script uses the protobuf-gradle-plugin Gradle plugin to generate Java source code from the Ballista protobuf file and this depends on the protobuf compiler being installed.

Use the following instructions to install the protobuf compiler on Ubuntu or similar Linux platforms.

wget https://github.com/protocolbuffers/protobuf/releases/download/v3.11.4/protobuf-all-3.11.4.tar.gz
tar xzf protobuf-all-3.11.4.tar.gz
cd protobuf-3.11.4/
./configure
make
sudo make install
sudo ldconfig

Build libraries

cd jvm
./gradlew publishToMavenLocal

Sample Data

Some of the examples in the book use the following data set.

wget https://nyc-tlc.s3.amazonaws.com/trip+data/yellow_tripdata_2019-12.csv