Users looking at Oracle alternatives see the limitations of PostgreSQL in terms of high availability and ask:
Will MongoDB give me the same high availability (HA), disaster recovery (DR), and zero/near-zero data loss I’ve relied on in Oracle’s Maximum Availability Architecture (MAA)?
I previously compared Oracle Maximum Availability Architecture with YugabyteDB’s built-in high availability features here. I've done the same with MongoDB, which also offers built-in high availability though Raft-based replication to quorum, but for a document-model application rather than SQL.
Oracle MAA and MongoDB
Oracle DBAs are used to a mature, integrated stack—RAC, Data Guard, GoldenGate, Flashback, and RMAN—refined for decades to work together in the MAA framework. MongoDB instead takes a cloud-native, distributed approach, embedding replication, failover, and sharding directly in its core engine rather than through separate options. While the technologies differ—MongoDB uses pull-based logical replication instead of broadcasting physical log changes—they pursue the same goals.
MongoDB vs Oracle MAA Levels
| MongoDB | Oracle🥉 MAA Bronze | Oracle🥈 MAA Silver | Oracle🥇 MAA Gold | Oracle💰 MAA Platinum | |
|---|---|---|---|---|---|
| Main Goal | Cloud-Native Resilience | Backup | MAA Bronze + HA | MAA Silver + DR | MAA Gold + Multi-Master |
| HA/DR Product | Native in MongoDB core: replica sets, sharding, multi-region, backups | RMAN | RAC | RAC + Data Guard (ADG) | RAC + Data Guard + GoldenGate |
| RPO (Recovery Point Objective) | 0 with writeConcern: "w:majority" (sync to quorum), which is the default | Minutes (archivelog backups) | Same as Bronze (no extra DB protection) | 0 with Maximum Protection0 or more with Maximum Availability | Seconds if tuned with low replication lag |
| RTO (Recovery Time Objective) | 5–15 seconds for automatic primary election | Hours–Days depending on database size | Seconds for server crash, but DB is not protected | Minutes with FSFO (Sync) | Seconds if no conflicts in active-active failover |
| Corrupt Block Detection | Automatic via storage engine checksums and replica healing | RMAN detection + manual blockrecover | No additional protection | Automatic with lost-write detection (ADG) | No additional protection beyond Gold |
| Online Upgrade | Zero downtime via rolling upgrades | Minutes–hours for major releases | Some minor rolling upgrades (OS/patch) | Near-zero downtime with transient logical | Yes, if GoldenGate active-active is configured correctly |
| Human Error Mitigation | Point-in-time restores from Atlas backups or filesystem snapshots | Flashback Database, Snapshot Standby, LogMiner, Flashback Query, Flashback Transaction, dbms_rolling, dbms_redefinition, ASM | Same + RAC | Same + ADG | Similar to Gold (GoldenGate can replay changes) |
| Online DDL | Non-blocking schema changes (document model) | No transactional DDL; EBR (Edition-Based Redefinition) | Same as Bronze | Same as Bronze | Same as Gold |
| Active-Active | Via sharded clusters or Atlas Global Clusters; shard-key design avoids conflicts | No — only standby server offline unless licensed | RAC active-active within the same datacenter | No — standby is read-only (Active DG) | Yes — GoldenGate active-active, requires conflict handling |
| Application Continuity | Automatic failover with drivers + retryable writes | CMAN proxy | Transparent failover + Transaction Guard (RAC) | Transparent failover (Data Guard) | Transparent failover + conflict handling |
| Complexity | Low (built-in distributed features) | Low | High (clusterware) | Medium (RAC + DG) | High (RAC + DG + GoldenGate) |
| Price (Options) | EE (~$50K/CPU) | EE + 50% (RAC option) | EE + RAC + 25% (ADG option) | EE + RAC + ADG + 75% (GoldenGate; often ~2.5× EE base) |
Understanding Oracle MAA Levels
Oracle’s Maximum Availability Architecture (MAA) is organized into four tiers, each building on the previous:
- 🥉 Bronze – Backup Only: RMAN online backups, archived log retention, manual restore. RPO in minutes to hours, RTO in hours or days.
- 🥈 Silver – Bronze + High Availability: Add Real Application Clusters (RAC) for server-level HA and limited rolling upgrades. Very low RTO for server failures but no additional database protection beyond Bronze’s backups.
- 🥇 Gold – Silver + Disaster Recovery: Add Data Guard (often Active Data Guard) for synchronous or asynchronous failover to remote standby. With FSFO (Fast Start Failover) in sync mode, RPO can be zero, RTO in minutes.
- 💰 Platinum – Gold + Multi-Master: Add GoldenGate logical replication for active-active writes across sites and versions. Enables global presence but requires manual conflict handling and careful design.
In Oracle’s world, HA/DR is not one thing — it’s a stack of separate licensed products you combine according to your needs and budget. The complexity and cost rise quickly as you move up the tiers.
Focus on features rather than product names, which can be misleading. For example, Autonomous Data Guard (RPO > 0, no real-time query, no rolling upgrade) in the Autonomous Database managed service differs from Active Data Guard, which provides all features of MAA Gold, but is not part of the managed service.
How MongoDB Builds HA and DR Natively
MongoDB’s availability model takes a fundamentally different approach: it is a distributed database by design, with no single authoritative copy bottleneck like a monolithic RDBMS. Replication, failover, sharding, and multi-region deployment are built in, not optional add-ons.
Key components:
- Replica Sets – Every MongoDB production deployment runs as a replica set by default.
- Automatic leader (primary) election in 5–30 seconds if a node fails.
- Tunable write concern for RPO control (e.g., "w:majority" for RPO=0).
- Flow control to throttle writes when majority committed replication lag reaches a threshold to prevent secondaries from falling too far behind
- Sharding – Horizontal partitioning with each shard itself being a replica set.
- Supports scaling out writes and reads while maintaining HA per shard.
- Multi-Region Clusters – Place replica set members in multiple regions/zones for DR.
- Writes propagate to remote members, optionally synchronously (Atlas global writes).
- Backups & Point-in-Time Restore – Atlas offers continuous cloud backups with PIT restore. Self-managed deployments use snapshots + Oplog replay.
- Automatic Failover & Driver-Level Continuity – Client drivers reconnect automatically. Retryable writes can resume after failover without application-level intervention.
- Rolling Upgrades Without Downtime – Upgrade nodes one at a time, keeping the cluster online.
This means that what takes three separate licensed Oracle products to achieve in Platinum is, with MongoDB, simply a topology decision you make when deploying the cluster.
Key Takeaways
- Oracle MAA levels are additive—Bronze, Silver, Gold, and Platinum. Each higher tier requires extra products and adds complexity for on‑premises deployments, and not all tiers are available in managed services. They are very mature for enterprises, but you should not underestimate the operational cost.
- MongoDB provides built-in HA and DR. Replication, failover, sharding, and multi-region deployments are topology settings that simplify operations. However, configuration still matters: consistency is tunable per application, and settings must align with your infrastructure’s capabilities.
- RPO and RTO targets achievable with Oracle Platinum are also achievable with MongoDB. The main difference is flashback capabilities, so you must tightly control production access and ensure all changes are automated and tested first in pre-production.
- MongoDB rolling upgrades eliminate downtime for routine maintenance—a major change from traditional monolithic upgrade windows. Avoid running outdated versions, as was common with legacy databases.
- Global write scenarios are possible in both, but MongoDB’s sharded architecture can automatically avoid conflicts (ACID properties over the cluster, causal consistency)
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