---
pattern_id: PAT-001
title: "OPTIMIZE TABLE on Galera triggers TOI DDL → Deadlock"
category: database
severity: high
status: active
first_observed: 2026-07
last_updated: 2026-08-30
related_systems: [galera-maxscale]
related_solution_docs:
  - docs/solutions/bug-fixes/2026-07-23-cnpg-timeline-corruption-rebuild.md
related_skills: []
---

# OPTIMIZE TABLE on Galera triggers TOI DDL → Deadlock

## Symptom

Running `OPTIMIZE TABLE` on a Galera cluster node causes a cluster-wide stall or deadlock.
The table lock propagates via TOI (Total Order Isolation) to all nodes, blocking all writes
to ALL tables during the operation.

## Root Cause

Galera executes DDL statements (including `OPTIMIZE TABLE`, `ALTER TABLE`, etc.) in TOI mode.
This means the DDL is replicated as a global operation that blocks the entire cluster — not
just the target table. For large tables, the rebuild phase can take minutes, causing apparent
outages.

## Mitigation

1. **Use RSU before DDL**: Switch the node to Rolling Schema Update (RSU) mode before running
   `OPTIMIZE TABLE`. This prevents cluster-wide blocking:
   ```
   SET GLOBAL wsrep_OSU_method = 'RSU';
   -- run OPTIMIZE TABLE on this node only
   SET GLOBAL wsrep_OSU_method = 'TOI';  -- restore
   ```
2. **Schedule during maintenance window** — even with RSU, the node itself is degraded
3. **Consider pt-online-schema-change** for large tables — avoids blocking entirely

## Prevention

- Never run `OPTIMIZE TABLE` or `ALTER TABLE` in production without RSU on Galera
- Add this check to DBA runbooks and monitoring alerts
- The Galera skill (`mariadb-galera-cluster-administration`) documents this pitfall

## Evidence

- Observed during Galera cluster administration sessions (Jul 2026)
- MEMORY.md entry: "OPTIMIZE TABLE=TOI DDL→Deadlock! RSU davor."
- Galera cluster: nodes 300/301/302, VIP .70:3306