# Greg Leclercq

> Principal Software Engineer at Roblox

Location: Mountain View, California, United States
Profile: https://flows.cv/gregleclercq

21 years of experience building systems and software to tackle some of the most challenging problems in startups, small, and large companies at a scale of millions and billions of users.

I build reliable and efficient systems to provide the infrastructure that enables products to delight users. I build and grow teams to work efficiently and sustainably to pursue that purpose.

Specialities:
 . Python, Golang, Rust, C/C++, JVM, TypeScript
 . Highly-reliable and efficient systems at scale (all my work experience, massive scale at Meta)
   . Migrated Meta's experimentation (A/B testing) platform backend to Presto. Powers analytics for features used by 3B people.
   . Design and architecture of systems on-prem and in the cloud (built the platform for Botify from scratch on AWS and currently building systems on AWS at Airtable)
   . Observability (all my work experience, most recent experiences at Meta and Airtable)
   . Low-level single machine performance (hardware, kernel, low-latency, and data processing)
   . Distributed systems performance and reliability (network, tooling, high-throughput data processing)
 . Kernel and Hypervisor development:
    . Improved the performance of AoE on linux, implemented RCU locking with a 30% increase of performance, maintained the AoE stack for a cloud host provider, fixed bugs, ported AoE stack across kernel versions)
   . Modified Xen block storage to implement credit scheduling and optimize I/O allocation between multiple VMs for a cloud hosting provider (Gandi).
 . Thorough understanding of operating systems (kernel development at work and personal projects), hardware architecture (driven by performance, security, os dev), and network protocols (worked on DCTCP and congestion avoidance at Facebook/Meta)

## Work Experience
### Principal Software Engineer @ Roblox
Jan 2023 – Present | San Mateo, California, United States
I lead the Scalability engineering team (engineering manager, formerly tech lead).

My team owns the TACO (squeeze load testing) and C3 (capacity prediction) systems mentioned in https://corp.roblox.com/newsroom/2025/06/roblox-infrastructure-supporting-record-breaking-games in addition to the load testing platform and rotrace, a tool that traces API HTTP requests from Roblox games to find inefficiencies and the impact of games on the Roblox platform.

We design and develop systems for:
- Capacity prediction, bottleneck detection, and performance analysis
- Load testing
- Squeeze testing

Our systems analyze production data and results from load testing with ML to provide prediction for scaling Roblox systems. We built a tailored system to scale for record-breaking growth driven by Grow a Garden and Steal a BrainRot.

I'm the co-creator, with Jan Berkold, and initial developer of the TACO squeeze testing system mentioned in https://corp.roblox.com/newsroom/2025/06/roblox-infrastructure-supporting-record-breaking-games. Went 0 to 1 from idea to first run in production in 3 weeks. Now running automated squeeze tests to prepare for major peaks.

### Staff Software Engineer @ Airtable
Jan 2019 – Jan 2022 | San Francisco Bay Area
Observability team.

Previously: provisioning, deployment pipeline, CI, containerization, mysql reliability, redis/caching reliability and performance.

As a member of the infrastructure group, I build software and systems to support reliability, scalability, and developer effectiveness with the goal of provided the best experience to Airtable's customers. I also work across functions to make reliability part of our processes and culture.

### Staff Software Engineer @ Facebook
Jan 2015 – Jan 2019 | Menlo Park, California
Production Engineering Tech lead (staff+ level leading 8 engineers) in the Presto team (~30 engineers, part of AI infra).

Facebook's data warehouse operates at exabyte scale. I've deployed the first largest Presto cluster in production.

- Technical leadership: defined the strategy and the roadmap. Grew the team. Mentored team members.
- Scalability and reliability of Presto in the Data Warehouse/Lake: exabytes of data, tens of thousands of machines.
- Migration of Facebook's A/B testing framework on Presto Raptor: hundreds of petabytes with < 30s p90 latency on experiments that impact billions of users. Clusters in multiples regions. Drove the reliability, scalability, and performance.
- Testing and deployment of DCTCP: the scale of Presto at Facebook and the amount of data it processed led to saturate the network. DCTCP is a congestion-avoidance protocol that allows to maximize both throughput and reliability.
- Non-disruptive deployments of Presto: I led the evolution of the deployment process to update Presto clusters without disruption (~10k internal daily active users) across datacenters.

- Automation, on boarding, and capacity management of ads products with Presto on sharded MySQL and Thrift: use case customer-facing dashboards and report for ads.
- Observability for Presto's infrastructure and query execution: with clusters executing complex SQL queries on thousands of distributed nodes, I developed new tools to scale debugging, monitoring, and address internal customer needs quickly. Deep debugging of the JVM and Presto internals.

- Maintainer of the Presto Python client library (https://github.com/prestodb/presto-python-client): I created the new Presto Python client library initially to support transaction and then to become the reference library.
- Community engagement with the Open Source community (F8 Classroom, The Diff Podcast, meetup, coordination, definition of processes).

### Founding Engineer / Head of Infrastructure @ Botify
Jan 2012 – Jan 2015 | Paris
Built the backend and infrastructure of the two core products from scratch. Grew the team and the culture.

Founding engineer, reported directly to the founders, member of the executives board, participated to the definition of the strategy, defined the development process, build, ran, and scaled the infrastructure. This was a hands-on role where I worked as a tech lead while also designing systems and writing a lot of code.

- Backend programming: log parsing in C/C++ (able to filter and parse tens of terabytes of data on a single machine in less than an hour) and Python, processing in Python (and prototypes in Scala with Spark).
- Created and developed a distributed workflow execution framework (Python, Amazon SWF, S3, EC2): powers the crawls and distributed computations. Implemented a dataflow model with Python code, horizontally scalable and resilient to failures.
- Distributed systems architecture on dedicated servers and in the cloud (built the platform from scratch on Amazon AWS)
- Optimization and troubleshooting of performance-intensive algorithms for data processing and analytics
- Configuration management with Puppet and Ansible
- Amazon AWS (EC2, S3, SWF, route53, ...) programming (custom tools and integration to applications) and architecture (automation and immutable/disposable servers)
- Linux system administration

### Founding Engineer / Software Engineer @ tinyclues
Jan 2011 – Jan 2012 | Paris Area, France
Founding engineer. Reported directly to the founders.

I co-developed a machine learning framework (Python, Scipy/Numpy) with a Python embedded DSL that compiled to computations running on AWS. Implemented a dataframe API in Python (before pandas existed).

### Software Engineer @ Gandi
Jan 2008 – Jan 2011
Tech lead on kernel engineering, the storage stack, and the hosting API.

Kernel, hypervisor, and backend engineering on one of the first cloud service created (AWS was created on 2006).

Kernel, hypervisor, storage, and hosting API. I joined during the early stages of the cloud hosting service (IaaS/EC2-like). 

- Launched and led the development of the Cloud Hosting API
- Backend programming in Python for the virtual machines (VMs similar to EC2 instances) lifecycle and storage management (EBS-like).
- Linux kernel programming: core software engineer of the internal ATA-over-Ethernet (aoeserver and aoeclient) implementation.
- Xen dom0 programming: added I/O throttling to the blkback module, improved storage performance and efficiciency for cloud hosting use cases.
- Xen troubleshooting: memory management, live migrations, xend bugs.
- Exploratory work in systems efficiency (storage, VM provisioning, unikernel).
- High-performance EBS-like block storage: C/C++, event-based (libev) server for remote block-device with copy-on-write, append-only writes, compression, and NBD.
- Mentored interns and junior engineers: memory management on 64-bit arch, unikernel, continuous integration.

### Network and Security Architect @ Orange
Jan 2004 – Jan 2008 | Guyancourt, 78, France
I worked at Orange/France Telecom in the service and corporate architecture division on platforms serving tens of millions of users (entire countries).

I defined the architecture, usage, and best practices of network security components such as firewalls, IDS and IPS, SIEM products for services with millions of users (email platform, IPTV, VoIP platforms, internal systems).

I assessed the security of internal systems, architectures, and products.

. Vulnerability Management
. Security Information and Event Management (SIEM)
. Network IDS testing and analysis
. Firewall {Security Policy, Implementation, Guidelines}
. Network Architecture Design
. Risk analysis
. Vulnerability assessment
. Security products evaluation (network and host security)

### Network and system administrator @ Formavenir Performance
Jan 2003 – Jan 2004
- TCP/IP network
- IPSec VPN
- Heterogenous (Debian GNU/Linux and MS Windows) Network administration
- DNS server, mail services, IM services implementation with open source Software
- Web development

### Open source engineer internship @ Linagora
Jan 2002 – Jan 2003
Developement of a secure and directory based mail solution based on Opensource Software using SMTP (+SASL Auth), LDAP, Kerberos V, IMAP, anti-spam (RBLs, spamassassin, bogofilter)


## Education
### System in Network and Security
EPITA: Ecole d'Ingénieurs en Informatique

### EPITA: Ecole d'Ingénieurs en Informatique


## Contact & Social
- LinkedIn: https://linkedin.com/in/gregleclercq
- GitHub: https://github.com/ggreg

---
Source: https://flows.cv/gregleclercq
JSON Resume: https://flows.cv/gregleclercq/resume.json
Last updated: 2026-04-12