Fix slow MongoDB queries - explain executionStats, COLLSCAN vs IXSCAN, compound index order with the ESR rule, covered queries and skip pagination
Fix Redis connection refused, auth errors, max clients and timeouts - bind and protected mode, slowlog, big keys, fork stalls and client settings
Troubleshoot Kafka consumer lag and rebalances - partition parallelism, max.poll.interval.ms, heartbeats, poison messages, offset commits and skew
Fix Celery tasks that are stuck, never run or run twice - broker URL, task registration, queue routing, prefetch, visibility timeout and acks_late
Fix AWS Lambda timeouts and cold starts - REPORT lines, VPC and NAT networking, client timeouts, memory and CPU, package size and provisioned concurrency
Fix 502, 504 and timeouts in Netlify and Vercel functions - read function logs, plan limits, background functions, bundling and response shape and size
Fix Python ModuleNotFoundError and ImportError - interpreter vs pip mismatch, virtualenv, package vs import names, relative imports and shadowed modules
Fix catastrophic regex backtracking and ReDoS - nested quantifier patterns, rewrites with atomic groups, input limits and linear-time engines like RE2
Avoid date, time zone and DST bugs - store UTC instants and IANA zones, handle DST gaps and overlaps, date-only values and epoch units
Fix mojibake and UnicodeDecodeError - recognize encoding mix-ups, decode at input and encode at output, UTF-8 in HTTP, MySQL utf8mb4, BOM and normalization
Never use floats for money - integer minor units or decimals, currency exponents, explicit rounding modes, cent-safe allocation and tax order
Fix Docker permission denied - docker.sock group access, bind mount UID/GID mismatch, named volume ownership, SELinux :z labels, rootless mapping
Fix git push rejected for files over 100 MB - find big blobs, filter-repo history rewrite, Git LFS migrate, size guards, secret rotation
Troubleshoot Cloudflare Tunnel - 1033 and 502 causes, ingress rules, Docker localhost trap, CNAME to cfargotunnel, token vs credentials
Fix a systemd timer that never runs - list-timers, enable the .timer, systemd-analyze calendar, Persistent, service journal, environment gaps
Fix WireGuard no handshake - key mismatch, UDP 51820 firewall, forwarding and NAT, AllowedIPs routing, overlapping subnets, keepalive, MTU
Docker ignores UFW - published ports bypass rules; bind to 127.0.0.1, DOCKER-USER chain, internal networks, reverse proxy, external nmap check
Fix pandas MemoryError on big CSVs - usecols, dtype and category, chunked aggregation, Parquet conversion, DuckDB and Polars lazy scans
Fix stale content behind a CDN - read Age and cache-status headers, Cache-Control per file type, hashed filenames, targeted purge, Vary traps
Design idempotency keys - unique key table, request fingerprint, in-progress 409, replay stored response, TTL, concurrent-duplicate tests
Fix common TypeScript errors - TS2339, TS2322, TS7006, TS2307 and possibly undefined; narrowing, @types, ESM extensions, tsconfig settings
Fix Prisma Migrate errors - drift, shadow database P3006, failed migration P3009 resolve, baselining an existing DB, dev vs deploy, directUrl
Fix SQLAlchemy DetachedInstanceError - session scope, selectinload eager loading, expire_on_commit, async MissingGreenlet, FastAPI session dependency
Fix Bash script bugs - set -euo pipefail limits, quoting and word splitting, safe loops, subshell variable loss, traps, cron PATH, ShellCheck
