AlloyDB vs. Cloud SQL: engineering guide to choose the right Google Cloud database for 2025

This post is maintained by Bytebase, an open-source database DevSecOps tool that can manage both AlloyDB and Cloud SQL. We update the post every year.

Update History	Comment
2025/05/13	Initial version.

Picking the right cloud database is key. Google Cloud offers a robust portfolio of relational database services, with AlloyDB and Cloud SQL being two prominent options for PostgreSQL and other popular database engines.

Both are fully managed, scalable, and highly available — but serve different needs:

AlloyDB: High-performance, built for demanding enterprise workloads.
Cloud SQL: Flexible, supports PostgreSQL, MySQL, and SQL Server.

Comparison Table#

Here is a summary comparison table to provide an at-a-glance overview of their key differences and strengths.

Feature	AlloyDB	Cloud SQL
Primary Focus	High-performance PostgreSQL for enterprise workloads	General-purpose managed database service
Supported Engines	PostgreSQL only	PostgreSQL, MySQL, SQL Server
Architecture	Cloud-native, disaggregated compute/storage, columnar engine	Managed VMs with persistent disk storage
Performance	4x faster transactions, 100x faster analytics vs standard PostgreSQL	Reliable performance, tunable with instance/storage choices
Elasticity	Fully elastic storage/compute, auto-scaling	Storage auto-growth, manual compute scaling
High Availability	99.99% SLA, < 60s failover, zero-downtime maintenance	Primary/standby HA, few minutes failover, scheduled maintenance
Analytics	Built-in columnar engine for HTAP	Standard engine capabilities, BigQuery integration
Pricing	Pay-as-you-go, a premium option focused on performance	Pay-as-you-go, tiered editions
Best For	Enterprise PostgreSQL, HTAP, mission-critical systems	General-purpose apps, multi-engine needs, lift-and-shift

Supported Databases#

AlloyDB only supports PostgreSQL. It's built for high performance and enterprise use, making it ideal for teams focused solely on PostgreSQL workloads.

Cloud SQL supports PostgreSQL, MySQL, and SQL Server. It's a fully managed option for teams needing flexibility across different database engines.

Summary: Choose AlloyDB for top-tier PostgreSQL performance. Choose Cloud SQL if you need support for multiple databases or prefer a different managed PostgreSQL experience.

Architecture#

AlloyDB uses a modern, cloud-native architecture with separate compute and storage. This design delivers high performance and scalability for PostgreSQL.

Distributed Storage: Built for PostgreSQL, with auto-scaling, fast I/O, and durable logs.
Independent Compute Scaling: Optimized compute with smart caching for low-latency access.
Built-in Columnar Engine: Supports fast analytics on transactional data (HTAP).
ML-Driven Management: Uses machine learning for tuning, maintenance, and vacuuming.

alloydb-disaggregation

Cloud SQL follows a traditional managed database model.

Managed VMs: Fixed-size instances per chosen database engine.
Persistent Disks: SSD or HDD storage, more tightly coupled with compute.
High Availability: Uses synchronous replication with auto-failover.
Read Replicas: Improve read performance and support multi-region replication.

Summary: Choose AlloyDB for top-tier PostgreSQL performance, scalability, and analytics. Choose Cloud SQL for a flexible, fully managed service that supports PostgreSQL, MySQL, and SQL Server.

Compatibility (Simplified)#

AlloyDB is fully PostgreSQL-compatible, designed to work with existing tools, queries, and drivers.

✅ Uses PostgreSQL wire protocol – works with JDBC, ODBC, psycopg2, etc.
✅ Supports standard PostgreSQL SQL syntax and many popular extensions
✅ Compatible with major PostgreSQL versions (e.g., 14, 15)
⚠️ Like other managed services, it restricts superuser access and direct file system use

Cloud SQL supports high compatibility across three engines:

PostgreSQL – Similar compatibility to AlloyDB
MySQL – Works with common tools and storage engines (e.g., InnoDB)
SQL Server – Supports .NET workloads and common SQL Server features

Things to Note:

🔍 Extension support: Varies between AlloyDB and Cloud SQL — always check if your required extensions are supported
🕒 Feature delays: Both may lag behind the latest open-source releases
🔒 Managed service limits: No OS access and limited administrative privileges in both

Summary: If you're using PostgreSQL and want full compatibility plus enhanced performance, AlloyDB is a great fit. If you need flexibility across PostgreSQL, MySQL, or SQL Server, or require broader engine support, Cloud SQL is the better option.

Performance#

AlloyDB is built for high-performance PostgreSQL workloads—both transactional and analytical.

🚀 Up to 4x faster than standard PostgreSQL for transactions (thanks to optimized write paths and smart caching)
📊 Up to 100x faster for analytics with its built-in columnar engine
📚 Supports many read replicas with very low lag (milliseconds)
🔁 Delivers consistent performance at scale due to its cloud-native architecture

Cloud SQL provides solid, general-purpose performance across PostgreSQL, MySQL, and SQL Server.

⚙️ Comparable to well-tuned, self-managed databases on cloud VMs
💡 Performance boosts available with Enterprise Plus for PostgreSQL
🔁 Supports read replicas and a variety of storage types (SSD, HDD, local SSD)
🔧 Performance tuning depends on instance size and storage config

Summary:

Choose AlloyDB if you need the best PostgreSQL performance, especially for high-throughput or real-time analytics. Choose Cloud SQL for reliable performance across multiple databases and customizable infrastructure options.

Elasticity#

Elasticity means how easily a database adjusts compute and storage to match workload demands. Both AlloyDB and Cloud SQL support elasticity, but AlloyDB is more dynamic - especially for storage.

AlloyDB offers high elasticity by design:

📦 Storage scales automatically with data — no need to pre-provision or resize
🧠 Compute resources (CPU/memory) can be resized quickly (few minutes)
📚 Read replicas can be added/removed to scale read throughput
📊 Columnar engine resources are also tunable for analytical load

Best for workloads with fast-growing or unpredictable storage and read demand

Cloud SQL offers moderate elasticity with some manual steps:

📦 Storage auto-growth expands disk as needed (no downtime), but cannot shrink automatically
🧠 Compute scaling requires instance restart — some downtime
📚 Read replicas available for PostgreSQL, MySQL, and SQL Server
⚙️ Serverless options are emerging but not yet broadly available

Good for steady workloads where occasional scaling is acceptable

Summary: Choose AlloyDB if you need seamless storage scaling and more flexibility with resource management. Choose Cloud SQL for broad database support and reliable, though slightly more manual, scaling features.

High Availability#

High Availability (HA) ensures your database stays online—even during failures or maintenance. Both AlloyDB and Cloud SQL offer strong HA, but AlloyDB is faster and more seamless.

AlloyDB: Built for 99.99% uptime, even during maintenance.

⚡ Fast failover: Detects failures and recovers in under 60 seconds
🌍 Regional resilience: Stores data across zones—automatic failover within region
🔁 Rolling maintenance: Updates with near-zero downtime
🌐 Cross-region replication: Supports disaster recovery with a synced secondary cluster

Best for critical apps needing fast recovery and minimal disruption

Cloud SQL: Reliable HA for PostgreSQL, MySQL, and SQL Server

⚙️ Primary + standby in different zones, with synchronous replication
🔄 Automatic failover: Usually within a few minutes
💾 Backups + PITR: Automated backups and point-in-time recovery
🌐 Cross-region read replicas: For DR, can be promoted to primary
🛠️ Maintenance windows: Patches may briefly interrupt service

Solid option for most production apps with moderate failover tolerance

Summary: Choose AlloyDB for faster failovers, lower maintenance impact, and higher SLA. Choose Cloud SQL for multi-engine HA and proven reliability across broader use cases.

Pricing#

Both AlloyDB and Cloud SQL use pay-as-you-go pricing, but AlloyDB is generally a premium option focused on performance, while Cloud SQL offers broader engine support and more flexible pricing tiers.

AlloyDB Pricing – Premium PostgreSQL service

💰 Compute: Pay for vCPUs and memory (per instance, region-based rates)
📦 Storage: Auto-scaling; pay only for what you use (no extra I/O charges)
💾 Backups: Charged by volume
🌐 Networking: Outbound traffic billed; in-region often free
🛡️ High Availability: Increases compute cost (storage is shared across zones)
📊 Columnar Engine: May add extra cost based on usage

Better price - performance for high-I/O PostgreSQL workloads due to smart architecture

Cloud SQL Pricing – Flexible for PostgreSQL, MySQL, SQL Server

💰 Compute: Charged by vCPUs and memory; multiple instance types
📦 Storage: Pay for provisioned SSD/HDD (IOPS may affect cost)
💾 Backups: Charged by size
🌐 Networking: Egress billed per standard GCP rates
🛡️ High Availability: Doubles compute/storage (primary + standby)
🧾 SQL Server Licensing: Included in cost (higher per vCPU)
📚 Read Replicas: Billed like standalone instances

More customizable pricing tiers and multi-engine support (but may require more tuning)

Summary: Use AlloyDB for PostgreSQL-only workloads needing top performance and efficient scaling—especially I/O-heavy apps Use Cloud SQL for multi-engine support, flexible pricing tiers, and broader use cases

💡 Use the Google Cloud Pricing Calculator to estimate your actual costs.

Here's a simplified cost example comparing Cloud SQL and AlloyDB for a PostgreSQL database in the us-east1 region, based on publicly available Google Cloud pricing as of 2025:

Region: us-east1
Workload: Medium production PostgreSQL workload
vCPUs: 4
Memory: 16 GB
Storage: 500 GB SSD
High Availability: Enabled
Backups: 100 GB
Usage: 730 hours/month (full-time use)

💰 Estimated Monthly Cost

Item	Cloud SQL (PostgreSQL)	AlloyDB
Compute	~$274.03 × 2 = $548.06 (HA needs 2 instances)	~$354.20 × 2 = $708.40 (HA setup)
Storage (500 GB SSD)	$85.00 ($0.17/GB/mo)	$100.00 ($0.20/GB/mo, regional & auto-scale)
Backup (100 GB)	$20.00 ($0.20/GB)	$20.00 ($0.20/GB)
Networking (egress)	Assume 100 GB × $0.12 = $12.00	Same = $12.00
Total (approx)	$665.06/month	$840.40/month

Recommended Setup#

The best setup for AlloyDB or Cloud SQL depends on your app's needs — but here are general best practices to get started efficiently and securely.

AlloyDB (for PostgreSQL) – Best for high-performance, enterprise workloads

⚙️ Instance sizing: Start at ~60–70% CPU usage; pick high-memory types for better caching
🛡️ Enable High Availability: Fast failover and resilient architecture
📚 Add read replicas for scaling read traffic
📊 Use columnar engine if doing analytics on transactional data
🌐 Private IP + Auth Proxy: Secure, low-latency connections
💾 Backups + PITR: Enable for disaster recovery
📈 Monitor: Track CPU, memory, query latency, storage, and replication lag via Cloud Monitoring

Cloud SQL (PostgreSQL / MySQL / SQL Server) – Best for general-purpose workloads

🛠️ Choose the right engine + version for your app
⚙️ Avoid shared-core machines for production; pick size based on actual usage
💾 Use SSD storage and enable auto storage increase
🛡️ Enable HA: Primary + standby in different zones
📚 Add read replicas if read-heavy
🌐 Private IP + Auth Proxy for secure, fast connections
🧰 Set up backups + PITR (binlog or full recovery)
🔒 Enforce SSL, strong passwords, and least-privilege access
🛠️ Set maintenance window to control patch timing
📈 Monitor + alert using Cloud Monitoring

For Both:

Test with real workloads before going live
Keep configs up to date as usage changes
Review costs + performance regularly
Apply least privilege to all users and services

Summary: Use AlloyDB for PostgreSQL apps needing top performance and scalability. Use Cloud SQL for flexibility across databases with solid managed features. Always plan for HA, security, monitoring, and growth from day one.