Piotr is available for hire

Piotr Kozłowski

Verified Expert in Engineering

Software Developer

Caminha, Portugal

Toptal member since September 10, 2015

Expertise

Back-end Developers Algorithms AWS RDS SQL PostgreSQL Java Python JSON Ruby on Rails Ruby Git Redis AWS Docker Machine Learning

Bio

Piotr is a seasoned software architect, entrepreneur, and developer specializing in efficient and scalable back-end systems, especially information retrieval and recommender systems. He has a knack for quickly incorporating new technologies, conceptualizing, innovating, and solving problems efficiently while focusing on business value. Piotr is a great team player with over a decade of experience leading teams of engineers.

Portfolio

Viemed Healthcare

Ruby on Rails 7, Amazon Web Services (AWS), Amazon Bedrock, HL7 FHIR Standard...

Patch

Clojure, Python 3, Databases, Apache Ignite, GraphQL, Azure, Snowflake...

Viemed Healthcare

TypeScript, GraphQL, PostgreSQL, Amazon Web Services (AWS), SMART on FHIR...

Experience

PostgreSQL - 16 years
JavaScript - 15 years
Python - 10 years
TypeScript - 8 years
Ruby on Rails (RoR) - 7 years
Functional Programming - 6 years
Clojure - 3 years
Multistage LLM Chains - 1 year

Availability

Part-time

Preferred Environment

MacOS, Linux, Git

The most amazing...

...system I've designed and built is a behavioral targeting platform. It collects users' online behavior and classifies them into interest groups.

Work Experience

Senior Software Engineer

2023 - PRESENT

Viemed Healthcare

Built an AWS-based scalable data processing system that analyzes patients' clinical notes to find essential details like hospital encounters, following appointments, etc.
Created a multi-stage RAG workflow that uses LLMs (with Amazon Bedrock) for advanced information retrieval from clinical notes, which gives medical staff a sophisticated insight into patients' respiratory situations.
Developed a web interface (using Ruby on Rails, Tailwind CSS, and Vue) that provides end users with the clinical notes' analysis results, including searching, document rendering, and feedback collection.

Technologies: Ruby on Rails 7, Amazon Web Services (AWS), Amazon Bedrock, HL7 FHIR Standard, Large Language Models (LLMs), Multistage LLM Chains, AWS Lambda, Vue 3, Tailwind CSS, Databases, Python, GitLab, API Integration, APIs, Database Design, Back-end, SQL, Product Management, Vue, Amazon RDS, Vite, Nuxt.js, SDKs

Senior Staff Software Engineer

2022 - 2023

Patch

Built a scalable data processing workflow that connected data lakes (Snowflake, Databricks, and others) to the custom, fast-access data system.
Created a Python-based CLI with a full-screen mode for configuring and inspecting data workflows.
Designed and built a data-mapping architecture for translating data streams between 3rd-party data sources and targets.

Technologies: Clojure, Python 3, Databases, Apache Ignite, GraphQL, Azure, Snowflake, Functional Programming, Apache Kafka, Python, API Integration, APIs, Database Design, Back-end, SQL

Senior Software Engineer

2018 - 2022

Viemed Healthcare

Assembled and led an international team that built a tablet app for patients who use noninvasive ventilators at home. The app connects them with respiratory caregivers and collects daily well-being surveys and ventilator usage data.
Developed a complete back-end system for the product, including a GraphQL server, vent data collection (TBs of data), and numerous integrations with 3rd-party services, such as video calls, FHIR servers, CRM services, etc.
Maintained 100% test coverage, hundreds of end-to-end tests, and a fully automated CI/CD workflow while building the back-end system.
Created and maintained SMART on the FHIR app, giving doctors access to patients' ventilator usage information.

Technologies: TypeScript, GraphQL, PostgreSQL, Amazon Web Services (AWS), SMART on FHIR, RabbitMQ, Databases, GitLab, API Integration, APIs, Database Design, Back-end, SQL, Product Management, Technical Leadership, Amazon RDS, SDKs

Founder, Consultant

2013 - 2022

Sandoy

Designed and developed a data feed verification system for an eCommerce customer from the fashion industry.
Designed and developed a system that manages the provisioning process for dental surgery offices.
Created an information hub for collecting weather data and an interface for real-time bidding (RTB) advertisement systems.

Technologies: ActiveMQ, MySQL, Couchbase, Ruby on Rails (RoR), Ruby, Java SE, Databases, API Integration, APIs, Database Design, Back-end, SQL, Vue, Vite, Nuxt.js, SDKs

Senior Back-end Engineer

2016 - 2018

Waldo Photos

Designed and developed a service for storing and comparing face descriptors using Python and Cassandra as a part of face recognition service.
Designed and developed a rule-based service for conversational (SMS/MMS) customer onboarding.
Created the high-performance image uploading and processing service for image normalizing, deduplication, thumbnailing, and EXIF-extraction.
Created a synchronous face detection service for selfie verification.
Co-developed a face detection and recognition service using Python, Redis, Kafka, and machine learning models.
Co-developed a multi-purpose data hub service processing tens of thousands of messages per second.

Technologies: Amazon Web Services (AWS), RabbitMQ, Apache Kafka, Redis, Cassandra, PostgreSQL, Clojure, Python, Java, Functional Programming, Databases, API Integration, APIs, Database Design, Back-end, SQL, Amazon RDS, SDKs

Co-founder, Architect, Developer

2014 - 2017

Vibrane

Designed and developed a system that collects a wide range of weather-related data from weather providers, meteorological institutes, historical climate data, and aviation weather services.
Designed and developed a system that analyzes collected data and then classifies current local weather conditions into segments. The segments reflect the subjective perception of different grades of "good" or "bad" weather and also how the weather is suitable for outdoor activities.
Designed and developed a system that tags online users with segments based on their geographical location.

Technologies: MapDB, Redis, Cassandra, MySQL, Ruby on Rails (RoR), Ruby, spray, Akka, Scala, Recommendation Systems, Databases, GitLab, APIs, Database Design, Back-end, SQL

Senior Back-end Engineer

2015 - 2016

Interstate Analytics (via Toptal)

Co-developed a distributed system that pulls in high traffic in visits, conversions, and digital ad spends.
Created a Ruby framework that integrates ad campaigns and marketing data with a third-party ad tech infrastructure.
Co-developed a Ruby on Rails-based dashboard for web analytics that combines website traffic data with ad campaigns spends, including several API endpoints.
Created a complete framework for unit and functional tests.
Created an application that manages computationally intensive machine learning jobs in a distributed environment.
Created a Shopify app that collects visits and purchases for further analysis.
Created an app module that pulls Salesforce data from Force.com API.

Technologies: Amazon Web Services (AWS), Segment.io, Docker, Amazon EC2, Amazon Simple Queue Service (SQS), AWS Lambda, NGINX, Redis, Citus, PostgreSQL, HTML5, CSS, Knockout (Knockout.js), jQuery, JavaScript, Jasmine, RSpec, Ruby on Rails (RoR), Python, Lua, Ruby, Databases, APIs, Database Design, Back-end, SQL

Chief IT Leader, CTO

2014 - 2015

Plagiat.pl (via Sandoy)

Designed and developed a RESTful API that provides anti-plagiarism services for learning management systems.
Designed and managed the development of the system that integrates the anti-plagiarism engine with National Repository of Diploma Writings (managed by Ministry of Higher Education). The system uses the algorithms that obfuscate the diploma content (it cannot be reconstructed after it leaves National Repository infrastructure) but still keeps anti-plagiarism analysis possible.
Managed a development of online diploma workflow system for universities.
Designed and developed the diploma archiving system using Apache Oak and MongoDB.
Redesigned the software development process in the company with continuous integration practices.
Designed and created a test automation framework that uses Docker containers for fully automated and 100% repeatable integration tests.

Technologies: GitHub, Sonar, Jenkins, PhantomJS, Docker, ActiveMQ, Apache Jackrabbit, Oak, MongoDB, Cassandra, MySQL, Ruby on Rails (RoR), Ruby, Java SE, RabbitMQ, Databases, GitLab, APIs, Database Design, Back-end, Product Management, Technical Leadership, Swagger

System Architect, Team Leader, CTO

2003 - 2014

Netsprint

Designed, led a team of developers, and managed a team of business consultants for a behavioral targeting system. The system collects (several thousand per second) online users' actions and then classifies them on the fly into groups of interests using collaborative filtering recommender techniques.
Designed, developed, and led a team of developers of enterprise-grade search system for eCommerce, corporate customers, and online publishers. The system includes full-text searching, faceted searching, automated category classification, and both content-based and collaborative recommendation.
Managed a team that created a social media monitoring system - the system that continuously crawled more than billion documents from blogs, forums, and social media. Users that subscribed for keywords were informed when new relevant documents appeared.
Designed and developed a system for classified ads management including full-text searching, faceted searching, collaborative filtering, and complex business dependency boosting rules.
Designed (as a Chief Architect), developed, and led a team of developers of a web search engine - the main alternative to Google Search in Poland.

Technologies: ActiveMQ, Redis, Cassandra, MySQL, Ruby on Rails (RoR), Ruby, Java EE, Java SE, C++, Recommendation Systems, Databases, API Integration, APIs, Database Design, Back-end, SQL, Product Management, Technical Leadership

Team Leader, Developer

1999 - 2003

Sensowne Systemy

Led the engineering team responsible for the online retail management system.
Designed and developed a product storage management system using Oracle technologies.
Designed and developed a retail product management system that consisted of the module for importing product description feeds from suppliers, a content management solution for product managers, and online product publishing.
Developed the modules that integrate the system with third-party providers of payment and delivery solutions.
Administered Oracle RDBMS including performance optimization, backup recovery, etc.

Technologies: Reports, Oracle Forms, Oracle RDBMS, PL/SQL, Java EE, Java SE, Recommendation Systems, Databases, APIs, Database Design, Back-end, Technical Leadership

Team Leader, Analyst, Programmer

1998 - 1999

Prószynski i S-ka

Developed an order processing module for the online bookstore.

Technologies: Reports, Oracle Forms, Oracle RDBMS, PL/SQL, Databases, APIs, Database Design, Back-end

Experience

Netsprint Audience

Netsprint Audience is a leading Polish DMP platform. It uses Behavioral Targeting System as a main engine that analyzes data from different sources and classifies them into behavioral patterns.

Netsprint Search

Netsprint Search in enterprise-grade search engine for eCommerce platforms, corporate customers, and online publishers.

Course Certificate: R Programming

https://www.coursera.org/account/accomplishments/certificate/UKK45WS9EQ

Offered by Johns Hopkins University and implemented via the Coursera MOOC platform.

Course Certificate: Machine Learning

https://www.coursera.org/account/accomplishments/certificate/85G86F5AW8R9

Offered by Stanford University and implemented via the Coursera MOOC platform.

Education

2010 - 2012

MBA Degree in Executive MBA

Warsaw University of Technology Business School - Warsaw

1995 - 2001

Master of Science Degree in Computer Science

University of Warsaw - Warsaw

Certifications

JANUARY 2017 - PRESENT

Machine Learning

Coursera

Skills

Libraries/APIs

Vue, Apache Jackrabbit, jQuery, Segment.io, PhantomJS, Java Message Service (JMS), Slick, spray, Vue 3

Tools

RSpec, GitLab, Apache Maven, NGINX, GitHub, ActiveMQ, Vim Text Editor, Scala IDE, Eclipse IDE, Vagrant, Jenkins, Git, Amazon Simple Queue Service (SQS), Amazon Elastic Container Service (ECS), RabbitMQ, Oracle Forms, Sonar, Citus, Apache Tomcat, Gradle, SonarQube, SMART on FHIR, Apache Ignite

Languages

Python, Java, Ruby, SQL, JavaScript, Bash Script, CSS3, HTML5, Clojure, TypeScript, Java SE, C++, Oak, Lua, CSS, Scala, GraphQL, Python 3, Snowflake

Frameworks

Ruby on Rails (RoR), Spring, Nuxt.js, Jasmine, Knockout (Knockout.js), Hibernate, Akka, Jersey, Ruby on Rails 7, Tailwind CSS, Swagger

Paradigms

Database Design, Functional Programming, HL7 FHIR Standard

Platforms

Amazon Web Services (AWS), Docker, JSE, Linux, Heroku, Apache Kafka, Ubuntu Linux, AWS Lambda, MacOS, Java EE, Amazon EC2, DigitalOcean, Azure

Storage

JSON, Redis, PostgreSQL, Cassandra, MySQL, PL/SQL, Oracle RDBMS, Couchbase, MongoDB, Databases

Other

Data Structures, Algorithms, Ad Serving, eCommerce, HTTP, API Integration, APIs, Back-end, Product Management, Technical Leadership, Amazon RDS, SDKs, Machine Learning, Vite, Reports, MapDB, Recommendation Systems, OpenRTB, Amazon Bedrock, Large Language Models (LLMs), Multistage LLM Chains

Collaboration That Works

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