Why doesn’t wrapping EF Core delete operations in a transaction prevent DbUpdateConcurrencyException during concurrent access?

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I have code that deletes records older than 30 days using an Entity Framework Core 6 DbContext. The deletion logic is executed concurrently from multiple places, and sometimes it throws a DbUpdateConcurrencyException with the message:

The database operation was expected to affect 1 row(s), but actually affected 0 row(s); data may have been modified or deleted since entities were loaded

I suspect that a race condition occurs where two processes identify the same old entities, but only one manages to delete them, causing the other to fail its concurrency check.

Here is the initial deletion code:

CSHARP
var expireBefore = DateTime.Now.AddDays(-30);
db.MyTable.RemoveRange(db.MyTable.Where(t => t.CreatedDate <= expireBefore));
await db.SaveChangesAsync();

To mitigate the issue, I wrapped the deletion code in a transaction with a serializable isolation level, assuming this would prevent the race condition. However, the exception still occurs occasionally. Below is the transaction version:

CSHARP
var expireBefore = DateTime.Now.AddDays(-30);
var executionStrategy = db.Database.CreateExecutionStrategy();

await executionStrategy.ExecuteAsync(async () =>
{
    await using var transaction = await db.Database.BeginTransactionAsync(IsolationLevel.Serializable);
    db.MyTable.RemoveRange(db.MyTable.Where(t => t.CreatedDate <= expireBefore));
    await db.SaveChangesAsync();
    await transaction.CommitAsync();
});

Why does placing the delete operations inside a transaction not prevent the concurrency exception?

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Answers 2

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2 Answers

Answer by StackOverflow TychoAI Agent • 1 month ago

The transaction doesn't prevent the concurrency exception because it doesn't change how EF Core uses optimistic concurrency. Even though you wrap your delete in a transaction with a high isolation level (Serializable), EF Core still keeps track of the expected number of rows affected for each entity. When two operations try to delete the same row concurrently, one may already have deleted it before the other commits. As a result, the second call detects that zero rows were affected instead of the expected one, triggering the concurrency exception.

The key points are:

Optimistic Concurrency: EF Core expects a specific number of rows to be affected (often one per deleted entity). If a row was already removed by another process, this expectation is violated, even if the transaction isolation level is high.
Transaction Isolation vs. Concurrency Control: While Serializable isolation will prevent dirty reads and other anomalies, it does not change the fact that your application logic, via the change tracker, is expecting a specific outcome. If multiple processes target the same rows, the optimistic concurrency check fails.
Race Conditions Still Possible: The transaction only ensures that within each transaction the operations are isolated. It doesn't serialize access across multiple transactions started concurrently from different contexts if they’re competing over the same set of rows.

To mitigate this, you could:

Handle the concurrency exception (for example, by ignoring it if the entity is already deleted).
Rethink the deletion process (e.g., using a single background job that performs the cleanup).
Use a raw SQL command to perform the deletion in one atomic operation, bypassing EF Core's change tracking and concurrency checks.

This way, your deletion logic won’t be interrupted by an optimistic concurrency check and the expected rows count won’t be enforced on a per-entity basis by EF Core.

Tycho is an AI agent, that grounds responses in various sources like documentation, code bases, live discussions, and relevant posts. Want to chat privately with Tycho?

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Answer by CometObserver721 • 1 month ago

The problem seems to be that you are using .Where to actually read the entities in, then mark them as removed and save the context. This is both inefficient and does not provide proper locking.

In the new versions of EF Core, you can just use an ExecuteDeleteAsync. This executes directly on the database without loading the data into the context, and should do the locking correctly.

CSHARP
var expireBefore = DateTime.Now.AddDays(-30);
await db.MyTable
    .Where(t => t.CreatedDate <= expireBefore));
    .ExecuteDeleteAsync();

If you really, really want to load the entities into the context, then firstly you need a WITH (UPDLOCK) or FOR UPDATE clause to get the correct locking (otherwise the shared lock won't stop someone else reading the data). And secondly you want to do this async.

You also need a transaction, but you don't need an execution strategy.

CSHARP
var expireBefore = DateTime.Now.AddDays(-30);
var query = db.MyTable
        .FromSql("SELECT * FROM dbo.MyTable WITH (UPDLOCK)")
        .Where(t => t.CreatedDate <= expireBefore);
await using var transaction = await db.Database.BeginTransactionAsync(IsolationLevel.Serializable);
db.MyTable.RemoveRange(await query);
await db.SaveChangesAsync();
await transaction.CommitAsync();

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Why doesn’t wrapping EF Core delete operations in a transaction prevent DbUpdateConcurrencyException during concurrent access?

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