MySQL 8.4 LTS Upgrade Guide (2025): Checklist, Risks, and Gains

MySQL 8.4 is the first Long-Term Support (LTS) release in the MySQL 8 family. For teams running 8.0 in production, 8.4 offers a stable target with extended support, security fixes, and operational improvements.

Why 8.4 LTS matters

• Extended support horizon for security and bug fixes
• Operational stability for long-lived estates
• Performance and observability improvements that reduce toil

Pre‑upgrade compatibility checklist

1. Inventory servers and versions (mysqld, connectors, clients, plugins).
2. Review removed/deprecated features from 8.0 → 8.4 release notes.
3. Audit SQL modes, character sets, collations, and time zones.
4. Check authentication plugins and TLS requirements.
5. Verify partitioning, generated columns, JSON paths, and GIS usage.
6. Confirm backup and restore process for current version.

Tip: capture query patterns with digest tables and performance schema ahead of time to compare pre/post behavior. If you use ProxySQL, its digest and stats views make this easy. See our read/write split guide here: ProxySQL Replication Read‑Write Split.

Upgrade strategy: In‑place vs logical

When to use in‑place (preferred)

• Same major family (8.0 → 8.4) with supported on-disk formats
• Strict downtime budget and large datasets
• Replication topology allows rolling restarts

When to use logical

• Cross‑platform moves or storage format concerns
• Schema cleanup or character set/collation changes
• Need for cross‑version validation prior to cutover

Rolling plan for large estates

1. Stand up staging that mirrors production topology and data scale.
2. Upgrade secondaries first. Validate replication, then promote/test.
3. Blue/green or replica-based cutover for primary.
4. Read traffic through a proxy layer (e.g., ProxySQL) for safe routing.
5. Gate writes during primary switch to prevent drift.

Validation plan

• Functional: application smoke tests, migrations, background jobs.
• Performance: TPS/latency with sysbench; compare digest outliers.
• Indexes and plans: verify plan stability for top N queries.
• Error budgets: watch deadlocks, lock waits, and error counters.

Post‑upgrade hardening

• Rebuild statistics as needed; verify ANALYZE behavior.
• Harden auth, TLS, and user roles; rotate credentials.
• Enable or tune slow log thresholds and sampling.
• Refresh backups; validate PITR and restore timing.

Common pitfalls to avoid

• Skipping release notes and deprecation notices.
• Upgrading primary first in a replicated topology.
• Assuming plan stability without comparing digest data.
• Neglecting connector/driver upgrades and TLS defaults.

Resources

• JSON changes and advanced usage in 8.x: 10 JSON Functions in MySQL 8
• Query routing and safe cutovers: ProxySQL Read‑Write Split

Need a second set of eyes?

If you’re planning a move to 8.4 LTS, we can help with assessment, rehearsal, and rollout. Contact us.