Financial Ledger Platform

Running analytical queries against the same PostgreSQL instance that serves OLTP traffic causes query plan interference, buffer cache thrashing, and lock contention. Analytical queries scan large row ranges; OLTP queries require point lookups. These access patterns are fundamentally incompatible at scale and must be separated before the interference causes P99 degradation.

Synchronous call chains that span more than 2-3 service boundaries create cascading latency exposure. When any downstream component degrades, the entire synchronous chain stalls. This is one of the most common contributors to unexpected P99 latency spikes and cascading failure in distributed systems.

Message queues or event streams that grow unboundedly under producer-consumer imbalance create memory pressure, increased recovery time, and operational ambiguity about whether the consumer is alive and processing. Backlog management must be designed in advance: retroactively adding it is operationally painful.

Read replicas introduce replication lag that creates silent stale-read windows. Lagged replicas serve data that may be seconds or minutes behind the primary. Applications that read from replicas without awareness of lag constraints can make incorrect decisions based on outdated state. The risk is highest for post-write reads, inventory checks, and financial operations.