SQL Azure Database retry logic

问题:

I have implemented the following code for handling INSERT/UPDATE retry logic with exponential backoff when writing to an Azure Database.

static SqlConnection TryOpen(this SqlConnection connection)
{
  int attempts = 0;
  while (attempts < 5)
  {
    try
    {
      if (attempts > 0)
       System.Threading.Thread.Sleep(((int)Math.Pow(3, attempts)) * 1000);
      connection.Open();
      return connection;
    }
    catch { }
    attempts++;
  }
  throw new Exception("Unable to obtain a connection to SQL Server or SQL Azure.");
}

However should I consider applying retry logic for my database reads as well? Or would the SqlCommand.CommandTimeout() method suffice? Most of my reads are instituted using the following code:

Dim myDateAdapter As New SqlDataAdapter(mySqlCommand)
Dim ds As New DataSet
myDateAdapter.Fill(ds, "dtName")

It's hard to know what sort of transient errors will occur in a production environment with Azure so I am trying to do as much mitigation as possible now.

回答1:

I think retries are going to be part of your Windows Azure SQL Database operations in general.

Rather than implementing a custom solution, have you looked at the transient fault handling application block published by Microsoft Patterns and Practices, specifically for SQL Database?

回答2:

Connection failures in SQL Azure are common. This is because your application will create a connection pool but while your side thinks these connections are over, Azure could terminate them at their end and you will never know about it.

They do this for valid reasons such as a particular instance has become overloaded and they are transferring connections to another one. With in-house SQL servers you generally never get this problem because your SQL Servers are always available and dedicated for your use.

As an example, I get about 5 connection failures with SQL Azure on about 100,000 database queries in a day.

It's going to happen with SQL Azure. If you are using ADO.NET then David's suggestion of transient fault handling is the way to go.

If you are going to use Entity Framework, there is good news and bad news: Transient Fault Handling with SQL Azure using Entity Framework

回答3:

I have implemented SqlConnection and SqlCommand extension methods providing retry logic. It is available on NuGet.