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A transport-level error has occurred (provider: TCP Provider, error: 0 - The semaphore timeout period has expired.)

I have read both these SO questions and the MS Docs:
Unexplained SQL errors in production environment - possibly network related
"The semaphore timeout period has expired" SQL Azure
https://learn.microsoft.com/en-us/azure/sql-database/sql-database-connectivity-issues#retry-logic-for-transient-errors
And have the same error. I did not have any of these in my ConnectionString:
ConnectRetryCount, ConnectRetryInterval or Connection Timeout.
This is a method of my DB class:
public DataTable ExecuteSqlCommand(SqlCommand com)
{
var retryStrategy = new Incremental(5, TimeSpan.FromSeconds(1), TimeSpan.FromSeconds(2));
var retryPolicy = new RetryPolicy<SqlDatabaseTransientErrorDetectionStrategy>(retryStrategy);
SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["DataContext"].ToString());
com.Connection = con;
SqlDataAdapter da = new SqlDataAdapter(com);
DataTable dt = new DataTable();
try
{
retryPolicy.ExecuteAction(() =>
{
con.Open();
da.Fill(dt);
});
}
catch (Exception e)
{
var telemetry = new TelemetryClient(); // app insights (azure)
telemetry.TrackException(e);
}
finally
{
con.Close();
}
return dt;
}
So what would be better? Remove the retry stuff from my code and use the attributes in my connection string? Let the framework do the work? Or is my current retry code sufficient? I have the feeling that the enterprise lib and retry stuff is obsolete, but cannot find a good source to confirm my thoughts.
I am using 4.7 and also have EF 6.2, but most queries are just SqlCommands using the code from above.

Make sure the user/login you use on your connection string has access to the master database on your Azure SQL Database server also, not only to the user database. That will provide faster connections and timeouts may disappear.
Using SQL Azure Execution Estrategy may help you with this issue.
public class MyConfiguration : DbConfiguration
{
public MyConfiguration()
{
SetExecutionStrategy("System.Data.SqlClient", () => new SqlAzureExecutionStrategy());
}
}
public class MyConfiguration : DbConfiguration
{
public MyConfiguration()
{
SetExecutionStrategy(
"System.Data.SqlClient",
() => new SqlAzureExecutionStrategy(1, TimeSpan.FromSeconds(30)));
}
}
For more information about SQL Azure Execution Strategy please visit this URL.

OdbcConnection ignores the ConnectionTimeout parameter

I need to ensure that, if database connection does not succeed in 10 seconds, the server will instead return an error.
This I did:
conn = new OdbcConnection("DSN="+DSN);
conn.ConnectionTimeout = 10;
try
{
await conn.OpenAsync();
}
catch(System.Data.Odbc.OdbcException e)
{
/// Handle error
}
But the server still hangs indefinitely when the database is not available.
How to ensure the timeout is respected?

Sql Connection Pool timeout

[Disclaimer] : I think I have read every stackoverflow post about this already
I have been breaking my head over this for quite some time now. I am getting the following exception in my asp.net web.api.
Exception thrown: 'System.InvalidOperationException' in mscorlib.dll
Additional information: Timeout expired. The timeout period elapsed prior to obtaining a connection from the pool. This may have occurred because all pooled connections were in use and max pool size was reached.
Most people suggested that I should look for leaked connections in my application. Here is my code. Now I am sure that I am not leaking any connections
public async Task<IEnumerable<string>> Get()
{
var ds = new DataSet();
var constring = "Data Source=xxx;Initial Catalog=xxx;User Id=xxx;Password=xxx;Max Pool Size=100";
var asyncConnectionString = new SqlConnectionStringBuilder(constring)
{
AsynchronousProcessing = true
}.ToString();
using (var con = new SqlConnection(asyncConnectionString))
using (var cmd = new SqlCommand("[dbo].[xxx]", con))
{
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.AddWithValue("#x1", 1);
cmd.Parameters.AddWithValue("#x2", "something");
await con.OpenAsync();
using (var rdr =await cmd.ExecuteReaderAsync())
{
if (rdr.HasRows)
{
ds.Load(rdr, LoadOption.OverwriteChanges, "MyTable");
}
rdr.Close();
con.Close();
ds.Dispose();
}
}
//I know this looks wrong, just an empty api method to show the code
return new string[] { "value1", "value2" };
}
The exception does not occur when I am using my local Sql Server. Only happens when I connect to our 'test server'. Are there anything else I can look at when trying resolve this issue. Like Sql server settings / network settings etc.
The stored procedure I call does not lock up the db I have checked for that as well. If that was the case it should have failed on my local Sql instance as well.
I am using jmeter to generate load, 1500 - threads(users). Surely I should be able to handle way more than that.
Thanks in advance

You have not specified any Connection Time out property, so it's 15 seconds default. using Max Pool Size=100 is not a good idea until you don't have proper hardware resources.
You started 1500 threads, so it seems that the some the threads keep waiting for 15 seconds to get their chance for connection opening. And as time goes out, you get the connection time out error.
So I think increasing the 'Connection Timeout' property in connection string may resolve your issue.

Cannot configure timeout from connection string

I have created this stored procedure in SQL Server 2008 R2:
CREATE PROCEDURE dbo.test AS
BEGIN
WAITFOR DEALY '00:00:40'
END
I have also written a C# console app to test the connect timeout property.
static void Main(string[] args)
{
OpenSqlConnection();
Console.ReadLine();
}
private static void OpenSqlConnection()
{
string connectionString = GetConnectionString();
using (SqlConnection connection = new SqlConnection(connectionString))
{
using (var command = new SqlCommand("dbo.test", connection) { CommandType = CommandType.StoredProcedure })
{
connection.Open();
Console.WriteLine("ConnectionTimeout: {0}", connection.ConnectionTimeout);
command.ExecuteNonQuery();
Console.WriteLine("Finished");
connection.Close();
}
}
}
static private string GetConnectionString()
{
return
"Data Source=test.com;Initial Catalog=test_db;Integrated Security=True;MultipleActiveResultSets=True;Connect Timeout=10; Application Name=Test";
}
There was a connection timeout exception returned as excepted (timeout in connection string < 40s). However, when I changed the Connect Timeout property to 120, I still got the same timeout exception. After some trial and error, it seems that the timeout value is always 30s regardless of my connection string value.
Is the connection timeout controlled by somewhere else? (if yes, where?)
Why the connect timeout value in connection string has no effect on my console app?
Update
Thanks all. I have just noticed that the command timeout is different from connection timeout(timeout in connection string).
Instead of changing my app.config, I would have to specify the CommandTimeout property as Sudipta Maiti suggested and recompile my code.
There is a similar issue in:
http://forums.asp.net/t/1197160.aspx?Can+you+change+command+timeout+via+the+connection+string+

Use CommandTimeout:
using (var command = new SqlCommand("dbo.test", connection) {
CommandType = CommandType.StoredProcedure })
{
connection.Open();
Console.WriteLine("ConnectionTimeout: {0}",
connection.ConnectionTimeout);
command.CommandTimeout = 120;
command.ExecuteNonQuery();
Console.WriteLine("Finished");
connection.Close();
}

I strongly suspect the given Timeout, it may not be enough to complete your operations. So make it Connection Timeout=30;
Connect Timeout -or- Connection Timeout by default the value will be 15 seconds. Based on your operation performance you might need to extend the seconds.
When a connection is returned to the pool, its creation time is compared with the current time, and the connection is destroyed if that time span (in seconds) exceeds the value specified by Connection Lifetime. This is useful in clustered configurations to force load balancing between a running server and a server just brought online.
A value of zero (0) causes pooled connections to have the maximum connection timeout.
There is a Sample Source almost same as yours.

SQL Server Error while pulling hundreds of records

I am getting this error when I try to get all the username password from production copied local database, I guess it is because of not closing the connection properly, but I am not sure how . I am using the Microsoft Enterprise Library, ant thought or comment about it?
Timeout expired. The timeout period elapsed prior to
obtaining a connection from the pool. This may have occurred
because all pooled connections were in use and max pool size was reached.
this is the mothod that is getting the username and password and producing the error.
private Model.UsernameandPass GetUsernamePass(string AccountNumber)
{
Model.UsernameandPass model = null;
string myConnection = System.Configuration.ConfigurationManager.ConnectionStrings[connectionName].ToString();
SqlDatabase db = new SqlDatabase(myConnection);
using (DbCommand command = db.GetStoredProcCommand("Get_TheUsernamePassWordFromProduction"))
{
db.AddInParameter(command, "AccountNumber", DbType.String, AccountNumber);
var result = db.ExecuteReader(command);
try
{
while (result.Read())
{
model = new Model.UsernameandPass();
model.Username = result.GetString(1);
model.Password = result.GetString(2);
}
}
catch (Exception ex)
{
}
}
db = null;
return model;
}
I am getting the error in this line after program runs for a while.
var result = db.ExecuteReader(command);

You're getting that error because a connection cannot be established, not only because they aren't being closed properly. Check permissions for the user you're trying to authenticate against the database with. Also be sure to call .open()/.close() when/if you are programatically opening/closing connections.
Check this link. You may want to increase your pool size, or check for long-running queries.