I have a database in azure which have standart s2 edition.In logs of my application I always see many exceptions such formats:
1.
System.Data.SqlClient.SqlException: The client was unable to establish a connection because of an error during connection initialization process before login. Possible causes include the following: the client tried to connect to an unsupported version of SQL Server; the server was too busy to accept new connections; or there was a resource limitation (insufficient memory or maximum allowed connections) on the server. (provider: TCP Provider, error: 0 - An existing connection was forcibly closed by the remote host.) ---> System.ComponentModel.Win32Exception: An existing connection was forcibly closed by the remote host
2.
System.Data.Entity.Core.EntityException: The underlying provider failed on Open. ---> System.InvalidOperationException: 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
3
System.Data.SqlClient.SqlException (0x80131904): The client was unable to establish a connection because of an error during connection initialization process before login. Possible causes include the following: the client tried to connect to an unsupported version of SQL Server; the server was too busy to accept new connections; or there was a resource limitation (insufficient memory or maximum allowed connections) on the server. (provider: TCP Provider, error: 0 - An existing connection was forcibly closed by the remote host.) ---> System.ComponentModel.Win32Exception (0x80004005): An existing connection was forcibly closed by the remote host.
I use SqlAzureExecutionStrategy so this exceptions are thrown after some number of retries.
I see different performance metrics on azure portla,but it seem they are ok.
How can I identify the problem?
I think that your database is under too heavy load, or you have some queries which are still running or not letting go of the connection.
I use this query to see what is running:
SELECT (SELECT TOP 1 SUBSTRING(s2.text,statement_start_offset / 2+1 ,
( (CASE WHEN statement_end_offset = -1
THEN (LEN(CONVERT(nvarchar(max),s2.text)) * 2)
ELSE statement_end_offset END) - statement_start_offset) / 2+1)) AS sql_statement,
s1.* FROM sys.dm_exec_requests s1
CROSS APPLY sys.dm_exec_sql_text(sql_handle) AS s2
ORDER BY 1
See if you have queries still running here or keep an eye on the CPU usage in the Azure portal.
The S2 databases aren't particularly good and it will throttle your requests so if you are doing lots of them (even small ones), it might be rejecting them.
Your retry strategy could also be making the problem worse, but throwing more requests at it when it has already been filled. You could try using an exponential back-off if this is the case.
All three could be explained by your connection pooling design. Are you re-using your connections, or is every call to the database opening it's own connection? Are you closing connections at the end of each DBContext? Are you implementing any kind of caching layer to reduce the number of round trips to your database to a minimum?
Here's a way to see if it is an issue with your pooling. From the portal go to the database in question, look at the Resource utilization graph, then hit edit.
Then add Sessions percentage and workers percentage from the select list, and hit OK.
If your pooling is an issue, you'll find that your sessions and workers percentages are high, and may be pegged at 100% for periods. If you hit 100%, you can be denied new connections for up to 5 minutes until the current sessions and workers either finish, or get killed off.
Related
I am executing a simple sql against Azure SQL server.
The list returns the correct number of items but then I get these 2 errors.
List<string> makes = _context.Cars.FromSql("select distinct(make) from cars").Select( l=> l.make).ToList();
A connection was successfully established with the server, but then an
error occurred during the login process. (provider: TCP Provider,
error: 0 - An existing connection was forcibly closed by the remote
host.)
An exception has been raised that is likely due to a transient
failure. Consider enabling transient error resiliency by adding
'EnableRetryOnFailure()' to the 'UseSqlServer' call.'
What is the issue ??
I used only "pure linq" and it works. It seems that there is an issue when trying to query SQL azure with both "pure linq" and "linq with FromSql" within the same context. Maybe the "linq with FromSql" tries to open/close a different connection.
List<string> makes = _context.Cars.Select(j => j.make).Distinct().ToList()
I have two mirrored SQL Servers (A and B for example).
I wrote a simple C# program (connect via SqlConnection), which insert rows into DB. When I make failover on server A, the program throws exception, then I try reconnect, and get exception by timeout (**A connection was successfully established with the server, but then an error occurred during the pre-login handshake. (provider: SSL Provider, error: 0**).
When I restart the app, the connection is successfully established (to server B). Next, I make failover on B server, and program throws exception, then I try to reconnect, and its work - connection to A witout restarting program.
My connection string:
Data Source=SERVER_A;Failover Partner=SERVER_B;Initial Catalog=TEST_DB;persist security info=True;user id=USER_LOGIN;password=USER_PASS;Connection Timeout=60;
I also try to set big timeout (60 seconds), and try to clear All sqlconnection pools, clear single pool by connection, but it is not working.
Interesting fact: if I use domain login and password, all works fine!
(user SID are same)
Hard to tell what your exact problem is. Perhaps it's that failovers aren't instant, and can't transfer query state - see https://dba.stackexchange.com/questions/27528/can-availability-groups-provide-seamless-failover-with-no-query-failures. If your application immediately retries the query the failover node may therefore still be in the process of taking over and therefore not ready to accept connections.
I'm constructing a query that joined a lot of tables. When I execute the query by select all columns, SQL Server throws an error
A transport-level error has occurred when receiving results from the server. (provider: TCP Provider, error: 0 - The specified network name is no longer available
When I replace the * with a few columns, it works fine. So I assume the problem is due to the result has exceeded the allowable size per row.
Now I'm wondering will it be ok to construct such a stored procedure and implement it in my WPF application?
Seems like you are having a timeout problem.
Have you seen this post?
In the link i added someone is claiming that the solution was to increase the "connect timeout" (Probably the select statement is taking too long).
If this does not solve your problem then you can try diagnosing it by:
1) Assume you were making remote connection, ping ,
telnet , or net view \ or see
firewall setting on the remote server to check whether the network is
still good to make sure remote server is still reachable, and contact
your network administrator to fix those problems.
2) You can give a retry by running your client app see whether the
problem went away.
3) If 1) and 2) passed, you might open sql profile to nail down which
client operation to cause sql server terminate connection, and check
server errorlog or application event log find out any clue.
If you were making local connection, it is probably reason 3).
Note: this is copied from the attached link.
Regarding whether you shold use a Stored Procedure check this post.
When I try to do the following code, the program hangs indefinitely. I don't know why and there seems to be other unanswered topics on the matter. Although, if the IP\website cannot be reached, then it works as intended.
private void DoStuff()
{
string connectionString = "Data Source=www.google.com;Connection Timeout=5";
using (SqlConnection connection = new SqlConnection(connectionString))
{
connection.Open(); //Hangs here indefinitely
Console.WriteLine("Test");
}
}
For example, if I set the connection string to
connectionString = "Data Source=www.nonexistentsite.com;Connection Timeout=5";
then it will throw an exception. How do I get it to throw an exception for an active site? ... Also google is just for testing purposes, obviously.
EDIT :
If I try to connect to an unreachable server name or IP address I WILL get this exception...
A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server)
UPDATE :
After letting the program run for quite a while, it usually times out finally after 3-5 minutes and gives me the error I posted above. How can I get it to timeout quicker?
If you have set an FQDN (Fully Qualified Domain Name) for your Data Source such as example.com and the DNS server is unable to resolve this FQDN for a long time it is pretty obvious that your request will hang out. Make sure that the machine from which you are running your application can reach the SQL server and resolve it without any issues. Also you probably want to make sure that there is no firewall that might be blocking the request.
Another possible cause for those symptoms is if you have exhausted the connection pool of ADO.NET. This could happen if you have many slow SQL queries running in parallel, each of them taking a physical connection to the database. There is a limit in the number of available connections on this pool and when this limit is reached the next call to connection.Open() might wait for an available connection to be returned to the pool.
Remark: you might also need to specify in your connection string how you want to authenticate against the SQL server. Checkout connectionstrings.com for more examples.
All this is to say that there is absolutely nothing wrong in the C# code you have posted in your question. It looks more like a network related problem that you could bring to the attention of your network administrators.
To get the connection to exit after a specified amount of time without success, you can use the Connection Timeout parameter in the connection string. The number you specify is in seconds, so for example, Connection Timeout=240 is equal to 240 seconds\60 seconds = 4 minutes.
Sample connection string:
<add name="MyConnectionString"
connectionString="
Data Source=MyServer\MSSQL2017;
Initial Catalog=MyDatabase;
Integrated Security=True;
Connection Timeout=10;"/>
In the above connection string, the Open() command will timeout after 10 seconds.
we are having some connection pool issues with Nhibernate on an MVC3 web application which is running with SQL Express and dealing with multiple concurrent AJAX based requests.
Every so often (hours in between) we see errors starting which show:
NHibernate.Util.ADOExceptionReporter
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.
then a load of
While preparing select TOP (#p0)
....
an error occurred
We have to recycle the IIS app pool to stop 500 errors from being thrown after that.
Looking at the SQL Server we see:
select * from sys.dm_exec_sessions
... gives about 30 sessions with IDs above 51 (i.e. user sessions)
select * from sys.dm_exec_connections
... gives around the same amount
BUT
select ##connections
... gives results with 79022
Is this indicating that the connections are never released?
The Nhibernate sessions are for the lifetime of the request.
Does anyone have any experience of anything like this or can point us in the right direction?
Many thanks
Richard
You can't have more then 32767 connection to SQL Server.
##CONNECTIONS also gives (my bold)
Returns the number of attempted connections, either successful or unsuccessful since SQL Server was last started.
Not current connection
I suspect that your pool is not set up correctly so it's exhausted too quickly.
Or you are not releasing connections correctly and you're checking SQL Server after you recycle IIS.