Tips to avoid hangfire jobs to duplicate?

Question

I am having a problem that some jobs on hangfire are been queued more than one time with the same parameters, the jobs are almost queued at the same time.

I've tried to limit the numbers of workers for just one and then to decorate my method with DisableConcurrentExecution.

I'm using sqlserver as storage. Anyone had faced this problem, there are some tips to avoid it?

PS: I used DisableConcurrentExecution because on hangfire documentation says that mutex and semaphores could not guarantee the job being called just one time.

PS2: Check my hangfire servers I note that i had two instances, each one with 1 worker, so I think its a parallelism problem not a concurrent one.

Answer 1

This work arround works for me. I used MaximumConcurrentExecutions(1) decorating the interface method that hangfire runs.

This didn't solve my problem alone, because of having multiple servers (auto scale up).

So in the startup class I create another backgroundjobserveroptions to create an exclusive server for this job, to guarantee that when the application scale up this did not create another server with another queue, I had to query in the sqlserver hangfire.server and check if my queue already exists.

if(!HangfireServerInfo.QueueExists("queuename", AppSettings.GetConnectionString("Hangfire"))){
        var hangfireServerOptions = new BackgroundJobServerOptions { WorkerCount = 1, Queues = new[] {"queuename"} };
        app.UseHangfireServer(hangfireServerOptions);
    }


public static class HangfireServerInfo
    {
        public static bool QueueExists(string queueName, string connectionString)
        {
            using (var connection = new SqlConnection(connectionString))
            {
                var cmd = connection.CreateCommand();
                cmd.CommandText = 
                    $@"SELECT COUNT(*) 
                    FROM {YOURHANGFIRESERVER.server}
                    WHERE JSON_QUERY(data, '$.queues') = '[""{queueName}""]'";

                connection.Open();
                var result = (int)cmd.ExecuteScalar();
                connection.Close();

                return result > 0;
            }
        }
    }

Probably that are better ways to solve it, but this works.