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Achievements

Achievement: YOLOAchievement: Pair ExtraordinaireAchievement: StarstruckAchievement: Pull Sharkx2

Achievements

Achievement: YOLOAchievement: Pair ExtraordinaireAchievement: StarstruckAchievement: Pull Sharkx2

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konstde00/README.md

Kostiantyn Dementiev

Systems researcher and platform engineer

I study tenant isolation in shared systems: when one tenant can read another's data, how to test for it, and what correct isolation costs.

ORCID · LinkedIn · Medium · Credly · konstde00@gmail.com

Research

Right now I'm measuring whether the optimizations that make multi-LoRA serving cheap also open channels between tenants, and what each defense costs in throughput.

Manuscripts, single-author:

  1. Adapter Identity in Multi-Tenant LLM Serving, in preparation. In 31 of 32 vLLM releases, same-named LoRA adapters of different tenants shared prefix-cache blocks. Keying the cache on a digest of the weights costs about 3% of throughput.
  2. Runtime Tenant Onboarding in Database-per-Tenant Spring Boot Applications, under review at IT&I 2026, Springer CCIS. Adds tenants to a running system without restarts.
  3. A Verification Protocol for Silent Tenant-Isolation Failures in Dynamically Routed Database-per-Tenant Applications, under review at Advances in Cyber-Physical Systems. It caught all 12 mutants, and the existing tests caught only 1.
  4. Per-Tenant Connection Pools as TTL Caches, under review at ACM SAC 2027.

Code for papers 2 to 4: runtime-tenant-onboarding
Smaller studies: retry-storm-metastability · observer-blur-coverage

Open source

I run released artifacts of recent systems papers (150+ so far) and send fixes upstream when something breaks. Merged fixes include:

  • Pie, a programmable LLM serving system: every session ran under the same name, so any client could list, attach to, or terminate other users' processes. PR #1101
  • SREGym: three grading oracles accepted wrong fixes. PRs #1107, #1108, #1109
  • ZMap (6.4k stars): a single BACnet or DNS reply could end a whole scan. PRs #984, #983
  • PyHealth (1.7k stars): its cleanup deleted other jobs' temp folders. PR #1296
  • Cleaning the NTP Pool, artifacts of a CCS 2026 paper: the IPv6 traceroute never probed the last hop limit. PR #1
  • Redash (29k stars): Google sign-in behind a load balancer that terminates TLS. PR #7178

Industry

Backend and platform engineer since 2022 at a digital analytics SaaS (26 data processing and reporting services, over 100 TB of data per year), doing most of its platform work since late 2023.

  • Replaced long-lived CI keys with OIDC roles across about 30 repositories, prototyped cross-customer isolation for the company's GitHub App, and helped with security hardening for SOC 2.
  • Found why tripling a tenant's concurrency limit from 10 to 30 left throughput flat (one audit per tenant per scheduler cycle) and proposed a bounded per-tenant admission rate.
  • Moved 11 services from Rancher to ECS and Fargate and 11 Jenkins pipelines to CircleCI, cutting AWS costs by 45% and incidents by over half.
  • Benchmarked four ways to read 2.1 million small S3 files. Compacting them with Athena before loading into Snowflake let a backfill that had failed after 4 hours finish in about 6 minutes, and a K-means model of object sizes showed that deleting early beat lifecycle expiry for 97% of files.
  • Cut a 10-table query over about 10 TB from 21 s to 2.1 s.

Recognition: Product and Engineering Team Member of the Year 2025 (Ukraine), Operational Excellence Champion in 3 of 13 quarters, Take Accountability award 2024, "Most Impactful" at the company's 2023 AI hackathon for an AI grammar and spelling checker.

Also founded OpsServing, a DevOps and cloud consultancy, in 2025. Java developer at Impltech, 2021-2022.

Education

BSc in Computer Science, Taras Shevchenko National University of Kyiv, 2025. One of the top 3 diploma marks in a group of 22 students, thesis graded 95/100. 1st place in the 2021 KNU Student Mathematics Olympiad.

Writing and community

Five articles on Medium (about 20,000 views) and one on DOU (3,000+ views). Volunteer DevOps engineer for Charity Hero. Built Ty yak?, a check-in app for air raids and other emergencies.

Stack

Python, Java, Spring, Scala, PyTorch, Kubernetes, AWS, Terraform, Docker, PostgreSQL, Kafka, GitHub Actions

Also vLLM, Hugging Face Transformers, PEFT, Snowflake, DuckDB, Amazon Athena, and CircleCI.

Certifications

AWS Certified Security Specialty CKS: Certified Kubernetes Security Specialist CKA: Certified Kubernetes Administrator CKAD: Certified Kubernetes Application Developer AWS Certified Solutions Architect Associate AWS Certified SysOps Administrator Associate AWS Certified Developer Associate HashiCorp Certified: Terraform Associate

  • 2026: AWS Certified Security Specialty, Certified Kubernetes Security Specialist (CKS), Snowflake SnowPro Core
  • 2025: Certified Kubernetes Administrator (CKA), Certified Kubernetes Application Developer (CKAD)
  • 2023: AWS Certified Solutions Architect, SysOps Administrator and Developer Associate, HashiCorp Certified: Terraform Associate

Pinned Loading

  1. multitenancy_overview multitenancy_overview Public

    The first implementation of runtime tenant onboarding, database-per-tenant. Superseded by runtime-tenant-onboarding.

    Java 20 20

  2. runtime-tenant-onboarding runtime-tenant-onboarding Public

    Tenant isolation under dynamic routing. Artefact behind one paper under review and two in preparation.

    Java 4

  3. demo-uni demo-uni Public

    Spring Boot service modelling a university as one Maven module per faculty, each owning its own domain, schema and migrations. Origin of the multi-tenancy work.

    Java 1

  4. genetic-timetable-scheduler genetic-timetable-scheduler Public

    University timetabling solved with a genetic algorithm. NestJS, Prisma, PostgreSQL. Teachers, groups, classrooms and preferences competing for a fixed set of slots.

    TypeScript

  5. number-theory-algorithms number-theory-algorithms Public

    Algorithms underlying public-key cryptography, from scratch in Java: primality, factorisation, discrete logarithm, elliptic curves, RSA.

    Java

  6. ty_yak_be ty_yak_be Public

    Backend for an emergency check-in service: one person asks whether the others are safe and each answers. Spring Boot, PostgreSQL, Liquibase, AWS SES, GitLab CI.

    Java