Why is DbContext not thread-safe, and what does DbContext Pooling do?

Short answer

The same DbContext instance cannot be used by two concurrent operations at once; AddDbContextPool reuses previously created context instances to reduce repeated construction costs.

Explanation

DbContext holds connection state and a Change Tracker that is not protected by concurrency locks. Running Task.WhenAll(db.Users.ToListAsync(), db.Orders.ToListAsync()) on one instance causes EF Core to throw an error. AddDbContextPool keeps a pool of checked and cleaned DbContext instances and recycles them across HTTP requests, noticeably improving requests per second.

Code example

// Enable pooling DbContext
builder.Services.AddDbContextPool<AppDbContext>(options =>
    options.UseSqlServer(connectionString));

Common mistakes

• Sharing one DbContext across concurrent threads or registering it as a Singleton.

Follow-up questions

• How does the EF Core Change Tracker work, and why should you use AsNoTracking() for read queries?

Sources

• Microsoft Learn — DbContext Pooling