improved scale-out algorithm

Author: yorek

app/Services/ScaleOut.cs

@@ -26,6 +26,7 @@ public class ScaleOut : IScaleOut
  private readonly ILogger<ScaleOut> _logger;
  private DateTime _lastCall = DateTime.Now;
  private string _lastConnectionString = string.Empty;
+ private List<String> _replicaConnectionString = new List<String>();
 
  public ScaleOut(IConfiguration config, ILogger<ScaleOut> logger)
  {
@@ -44,6 +45,7 @@ public string GetConnectionString(ConnectionIntent connectionIntent)
 
  var rnd = new Random();
 
+ // Get the list of available named replica from the primary replica
  // Add some randomness to avoid the "thundering herd" problem
  if (elapsed.TotalMilliseconds > rnd.Next(3500, 5500))
  {
@@ -57,25 +59,26 @@ public string GetConnectionString(ConnectionIntent connectionIntent)
  commandType: CommandType.StoredProcedure
  ).AsList();
 
- if (databases.Count > 0)
+ _replicaConnectionString = new List<string>();
+ foreach(var d in databases)
  {
- var i = rnd.Next(databases.Count);
- database = databases[i];
- _logger.LogDebug(database);
+ var csb = new SqlConnectionStringBuilder(connString);
+ if (!string.IsNullOrEmpty(d))
+ csb.InitialCatalog = d;
+ 
+ _replicaConnectionString.Add(csb.ToString());
  }
- } 
-
- var csb = new SqlConnectionStringBuilder(connString);
- if (!string.IsNullOrEmpty(database))
- csb.InitialCatalog = database;
- 
- result = csb.ConnectionString;
 
- _lastCall = DateTime.Now;
- _lastConnectionString = result;
- } else {
- result = _lastConnectionString;
+ _lastCall = DateTime.Now;
+ } 
  }
+ 
+ // Get a connection string randomly
+ if (_replicaConnectionString.Count > 0)
+ {
+ var i = rnd.Next(_replicaConnectionString.Count);
+ result = _replicaConnectionString[i];
+ } 
 
  return result;
  }