Connection Pool Tuning Under Load: How HikariCP Defaults Silently Kill Your Mobile Backend

--- title: "Connection Pool Tuning: How HikariCP Defaults Silently Kill Your Mobile Backend" published: true description: "A hands-on guide to instrumenting, detecting, and fixing HikariCP connection starvation under bursty mobile traffic with Micrometer, PgBouncer, and adaptive pool sizing." tags: kotlin, postgresql, architecture, performance canonical_url: https://blog.mvpfactory.co/connection-pool-tuning-hikaricp-mobile-backend --- ## What We're Building By the end of this tutorial, you'll have a Ktor service with a properly instrumented HikariCP pool, a PgBouncer layer for connection multiplexing, and an adaptive pool sizer that responds to real traffic — not a formula written for a different workload. Let me show you a pattern I use in every project that handles mobile traffic at scale. ## Prerequisites - Kotlin + Ktor project with `ktor-server-metrics-micrometer` - PostgreSQL 15+ - PgBouncer installed (`apt install pgbouncer` or your package manager) - Familiarity with HikariCP b