What causes sudden API latency spikes?

Common causes include database query degradation, upstream service slowdowns, GC pauses, connection pool exhaustion, and increased traffic without auto-scaling.

How do I measure API latency accurately?

Use distributed tracing tools like OpenTelemetry to capture P50, P95, and P99 latency per endpoint. Avoid relying solely on averages as they hide tail latency.

Fix API Latency Spike — Diagnose & Resolve Slow Endpoints

Direct answer

API latency spikes occur when a bottleneck appears in the request path — typically slow database queries, exhausted connection pools, or degraded upstream services. Use distributed tracing to isolate the slowest span and address that component directly.

Structured breakdown

Cause

API latency spikes are usually caused by slow database queries, missing caches, or upstream service degradation. Profile with distributed tracing to find the slowest span, then address the bottleneck directly.

Fix

Enable distributed tracing (OpenTelemetry, Datadog) and identify the slowest spans
Add database indexes on columns used in WHERE and JOIN clauses
Implement Redis or in-memory caching for frequently requested data

Outcome

API response times return to baseline with the identified bottleneck resolved.

Common causes

Slow or unindexed database queries under load
Missing response caching for repeated requests
Upstream service degradation or timeout cascading
Thread pool or connection pool exhaustion
Garbage collection pauses in the application runtime

Fix steps

1
Enable distributed tracing (OpenTelemetry, Datadog) and identify the slowest spans
2
Add database indexes on columns used in WHERE and JOIN clauses
3
Implement Redis or in-memory caching for frequently requested data
4
Increase connection pool sizes and add proper timeout configurations
5
Parallelize independent API calls with Promise.all instead of sequential await

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Frequently asked questions

These examples show the commands, logs, and configuration patterns most often used to verify this issue.

Command examples

curl -w 'time_total: %{time_total}s ' -o /dev/null -s https://api.example.com/endpoint
SELECT query, calls, mean_exec_time FROM pg_stat_statements ORDER BY mean_exec_time DESC LIMIT 5;

Log snippet

[WARN] Request to /api/users took 3200ms (threshold: 500ms)
[ERROR] Connection pool timeout after 30000ms

Config snippet

pool:
  max: 20
  idleTimeoutMillis: 30000
  connectionTimeoutMillis: 5000