Armen Ghazaryan

• Performance under load

  Performance work on Java services in production: p99 latency and throughput tuning for services on Kubernetes at Picsart, profiling and JVM tuning, and query optimisation over large data volumes at Synopsys.

  • p99 latency
  • Throughput
  • Profiling
  • JVM tuning

• Payment security

  Three and a half years on 3-D Secure 2.x at Worldline: challenge and frictionless authentication, liability shift, exemptions and soft declines under PSD2 and SCA, and integrations with acquirers and issuers on the critical transaction path. PCI DSS, secure coding, audit-ready logging and fraud-prevention logic in high-availability systems.

  • 3-D Secure
  • EMVCo
  • PSD2
  • SCA
  • PCI DSS
  • Fraud prevention

• Distributed systems at scale

  Microservices and event-driven pipelines on Kafka for a platform with 150M+ monthly active users and tens of thousands of requests per second, over MongoDB, Redis and Elasticsearch, on Kubernetes. Before that, Kafka for event-driven processes at Worldline, and large data volumes in Cassandra and Elasticsearch at Synopsys.

  • Kafka
  • Microservices
  • Event-driven architecture
  • Kubernetes
  • MongoDB
  • Redis
  • Elasticsearch
  • Cassandra

23 decisions behind this site, each written up as a record: what prompted it, what was chosen and what it costs. And how I review code: a pull request with my review, or the problems to find yourself.

• Reviews and mentoring

  At Picsart I review code and mentor mid-level engineers. At Worldline, code review was part of the work as well.

• Production

  At Picsart I take part in CI/CD, observability with Datadog and ELK, and p99 latency and throughput tuning for services on Kubernetes. At Worldline I was on the on-call rotation for high-availability payment systems.

• Architecture

  At Picsart I take part in architecture decisions on scalability and resilience.

• Payment security

  Frictionless or challenge?

  Before a card payment is authorised online, the bank’s access control server decides: let it through, ask for a code, or refuse. Send one a payment and watch it decide, rule by rule.

  Runs on

  The JVM behind this site

  Evidence for

  Three and a half years on 3-D Secure 2.x at Worldline: challenge and frictionless flows, exemptions, soft declines

• JVM performance

  Anatomy of a memory leak

  An unbounded cache looks harmless until the old generation fills up. Flip on the fix and watch the pauses disappear.

  Runs on

  Your browser, and the JVM behind this site

  Evidence for

  Performance profiling and JVM tuning

• JVM performance

  Where does the time go?

  Run a slow piece of Java on the JVM behind this site and read its Flight Recorder profile as a flame graph. Then run the fix.

  Runs on

  The JVM behind this site

  Evidence for

  Performance profiling, and p99 latency tuning at Picsart

• Payment security

  Charged twice

  Networks drop responses and clients retry. Without idempotency keys some customers pay twice — make the network worse and count them.

  Runs on

  Your browser

  Evidence for

  The edge cases of the critical transaction path at Worldline

• Distributed systems

  Ten thousand blocking calls

  The same workload on a fixed thread pool and on virtual threads, running live on the Java 25 JVM behind this site.

  Runs on

  The JVM behind this site

  Evidence for

  Java 21 and its virtual threads

• JVM performance

  Ten thousand threads, twenty connections

  Virtual threads made threads cheap; connections are not. Requests pour into a small PostgreSQL pool under three policies, and the ceiling stays where Little’s law puts it.

  Runs on

  The JVM behind this site

  Evidence for

  Throughput tuning for services on Kubernetes at Picsart