✅ EF Core long running query causing concurrency issues

Hello. I have a .NET application that uses a DbContext with PostgreSQL. To test the performance of my app, I added a million rows to one of the tables.

I noticed that it takes a pretty long time to fetch all of these rows, and if I run the method to get all the rows again before the previous query finishes, it throws the following exception:

System.InvalidOperationException: A second operation was started on this context instance before a previous operation completed. This is usually caused by different threads concurrently using the same instance of DbContext.

System.InvalidOperationException: A second operation was started on this context instance before a previous operation completed. This is usually caused by different threads concurrently using the same instance of DbContext.

This is an example of how it is set up currently:

private MyDbContext _dbContext;

public DbService(MyDbContext dbContext)
{
  _dbContext = dbContext ?? throw new ArgumentNullException(nameof(dbContext));
}

// This method throws the excpetion if called again before the previous query is finished
public async Task<List<MyObj>> GetAllObjects()
{
  return await _dbContext.MyTable.AsNoTracking().ToListAsync();
}

private MyDbContext _dbContext;

public DbService(MyDbContext dbContext)
{
  _dbContext = dbContext ?? throw new ArgumentNullException(nameof(dbContext));
}

// This method throws the excpetion if called again before the previous query is finished
public async Task<List<MyObj>> GetAllObjects()
{
  return await _dbContext.MyTable.AsNoTracking().ToListAsync();
}

✅ EF Core long running query causing concurrency issues

System.InvalidOperationException: A second operation was started on this context instance before a previous operation completed. This is usually caused by different threads concurrently using the same instance of DbContext.

System.InvalidOperationException: A second operation was started on this context instance before a previous operation completed. This is usually caused by different threads concurrently using the same instance of DbContext.

This is an example of how it is set up currently:

private MyDbContext _dbContext;

public DbService(MyDbContext dbContext)
{
  _dbContext = dbContext ?? throw new ArgumentNullException(nameof(dbContext));
}

// This method throws the excpetion if called again before the previous query is finished
public async Task<List<MyObj>> GetAllObjects()
{
  return await _dbContext.MyTable.AsNoTracking().ToListAsync();
}

private MyDbContext _dbContext;

public DbService(MyDbContext dbContext)
{
  _dbContext = dbContext ?? throw new ArgumentNullException(nameof(dbContext));
}

// This method throws the excpetion if called again before the previous query is finished
public async Task<List<MyObj>> GetAllObjects()
{
  return await _dbContext.MyTable.AsNoTracking().ToListAsync();
}

✅ EF Core long running query causing concurrency issues

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✅ EF Core long running query causing concurrency issues

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