Multi-tenant SaaS: Practical comparison — Database-per-tenant vs Shared Schema

In this article we compare two common multi-tenant database strategies — database-per-tenant and shared-schema — and give practical guidelines for choosing one depending on scale, operations, and compliance needs.

Quick summary

Here’s the short version before we dive in:

• Database-per-tenant gives strong isolation, simpler backups, and easier tenant-level scaling, but increases operational overhead.
• Shared schema is cheaper and simpler to operate for many tenants, but requires careful design for security, migrations, and scaling.

Core trade-offs

Let’s break down the important factors: isolation, cost, migrations, operational complexity, and scalability.

1. Isolation

• Database-per-tenant: Each tenant has its own database instance. Great isolation; one tenant’s heavy query load won’t affect others (barring shared host limits).
• Shared schema: All tenants share the same database and tables, typically keyed by TenantId. Isolation relies on application logic and row-level security where available.

2. Cost & operations

Database-per-tenant may multiply your infrastructure footprint (and costs). Shared schema reduces per-tenant resources but complicates operations in other ways.

1. Provisioning: database-per-tenant requires automation (provision DB, run schema migrations, seed tenant data).
2. Backups: per-tenant backups are easier with dedicated DBs.
3. Migrations: shared schema requires careful, backward-compatible migrations.

Practical examples (C# snippets)

Example: resolving tenant connection string in ASP.NET Core (simplified):

// Tenant resolution and per-tenant connection string (simplified)
public class TenantInfo
{
    public string TenantId { get; set; }
    public string ConnectionString { get; set; }
}

public class TenantProvider : ITenantProvider
{
    public TenantInfo GetCurrentTenant(HttpContext context)
    {
        var host = context.Request.Host.Host; // tenant.example.com
        // lookup tenant connection string from config/cache
        return new TenantInfo { TenantId = "acme", ConnectionString = GetConn(host) };
    }
}

Inline helpers are small but handy: use TenantId, DbContextFactory, and pattern like UseId when mapping tenant-scoped entities.

Schema migration strategy

Migration strategy differs between approaches. Here’s a compact checklist:

UX & operational playbook

• Automate tenant provisioning (infrastructure as code + templates).
• Use feature flags during migrations for schema changes that require coordination.
• Expose health & quota metrics per tenant.

Block quotes & references

“Architecture is about making trade-offs; every choice simplifies some things and complicates others.”

— System Architect

Inline code examples

Use inline code for identifiers: e.g., TenantId, ConnectionString, DbContextOptions. These are small but help readers scan technical text.

Lists & nested lists

Checklist for choosing an approach:

1. Does each tenant require strict data isolation?
   • If yes → lean toward database-per-tenant
   • If no → shared schema is fine
2. How many tenants do you expect? (hundreds vs millions)
3. Operational maturity (can you automate multi-DB routines?)

Images and diagrams

Advanced patterns

A hybrid approach is often practical: use shared schema for small tenants and offload high-value tenants to dedicated databases. This gives the best of both worlds when automated provisioning is available.

Common pitfalls

• Assuming network I/O is negligible — monitor per-tenant load.
• Ignoring migration compatibility — always design backward-compatible schema changes.
• Not testing tenant isolation thoroughly (include pen-testing for row-level security).

Final recommendation

There is no one-size-fits-all answer — choose based on your operational capacity, compliance needs, and business model. Start simple, automate early, and introduce tenant-level separation when the business justifies the cost.

If you want, I can convert parts of this article into reusable Gutenberg blocks (Tip, Warning, Diagram) so you can author consistent posts quickly.