Refresh the database connection if connection drops or times out - database

I have a Symfony command line task that has a habit of dropping the mysql connection.
Its a data import task. Which fetches data from multiple connections. Its not one big query but a few smaller ones.
It seems to drop the connection the first time it is ran. About half way through the script. However the second time its ran (from the beginning) it always completes the task.
Its not timing out on the query as the error response I get is that the connection has been dropped and it runs ok on its own. So im thinking that its some kind of timeout issue that is avoided when its ran the second time due to query caching speeding up the script.
So my question is how do I refresh the database connection?
[Doctrine\DBAL\DBALException]
SQLSTATE[HY000]: General error: 2013 Lost connection to MySQL server during query

A different approach is to check if Doctrine is still connected to the MySQL server through the ping() method in the connection. If the connection is lost, close the active connection since it is not really closed yet and start a new one.
if(FALSE == $em->getConnection()->ping()){
$em->getConnection()->close();
$em->getConnection()->connect();
}

I guess you mean to connect to the database if the connection is lost for some reason. Given an EntityManager, you can do it the following way:
$success = $_em->getConnection()->connect();
With getConnection, you are retrieving the connection object doctrine uses (Doctrine\DBAL\Connection), which exposes the connect method.
You can call connect anytime, as it checks wether a connection is already established. If this is the case, it returns false.
There is also a isConnected method to check wether a connection is established. You could use that to see where exactly the connection is dropping to get a clearer picture of what is happening.

Related

Visual Studio Server Explorer not closing sqlsrvr.exe process

I have this 'issue' since a long time and I am really wondering if this is just me or if there actually is a way of preventing the following:
UPDATED
In Visual Studio, when using the Server Explorer on a .mdf database, in a Entity Framework Code first approach project whenever I am opening the Database manually to see the data of certain tables (clicking on Show table data), it seems that even when I close the connection like this:
the database connection stays open somehow in the background.
I am getting "... the Database is currently in use ..." error if wanting to debug afterwards, after closing the connection, even when restarting the solution.
When I close all sqlservr.exe process(es) in the Task manager that does the trick.
Note that this is a local solution and a local database (.mdf) i am using for testing purposes. Nothing or no one else is using this solution.
I am quite sure this is not the behavior it should have right?
What am I doing wrong or what can I do to not have this behavior if this is not by default?
Thank you in advance for any feedback!
Include the "Pooling" flag in the connect string set to false:
Pooling=False
However, this might not be the best option in a productive environment:
Connection pooling reduces the number of times that new connections must be opened. The pooler maintains ownership of the physical connection. It manages connections by keeping alive a set of active connections for each given connection configuration. Whenever a user calls Open on a connection, the pooler looks for an available connection in the pool. If a pooled connection is available, it returns it to the caller instead of opening a new connection. When the application calls Close on the connection, the pooler returns it to the pooled set of active connections instead of closing it. Once the connection is returned to the pool, it is ready to be reused on the next Open call. (...) SQL Server Connection Pooling (ADO.NET)

Error 17886 - The server will drop the connection

We are running a website on a vps server with sql server 2008 x64 r2. We are being bombarded with 17886 errors - namely:
The server will drop the connection, because the client driver has
sent multiple requests while the session is in single-user mode. This
error occurs when a client sends a request to reset the connection
while there are batches still running in the session, or when the
client sends a request while the session is resetting a connection.
Please contact the client driver vendor.
This causes sql statements to return corrupt results. I have tried pretty much all of the suggestions I have found on the net, including:
with mars, and without.
with pooling and without
with async=true and without
we only have one database and it is absolutely multi-user.
Everything has been installed recently so it is up to date. They may be correlated with high cpu (though not exclusively according to the monitors I have seen). Also correlated with high request rates from search engines. However, high cpu/requests shouldn't cause sql connections to reset - at worst we should have high response times or iis refusing to send response.
Any suggestions? I am only a developer not dba - do i need a dba to solve this problem?
Not sure but some of your queries might cause deadlocks on the server.
At the point you detect this error again
Open Management Studio (on the server, install it if necessary)
Open a new query window
Run sp_who2
Check the blkby column which is short for Blocked By. If there is any data in that column you have a deadlock problem (Normally it should be like the screenshot I attached, completely empty).
If you have a deadlock then we can continue with next steps. But right now please check that.
To fix the error above, ”MultipleActiveResultSets=True” needs to be added to the connection string.
via Event ID 17886 MSSQLServer – The server will drop the connection
I would create an eventlog task to email you whenever 17886 is thrown. Then go immediately to the db and execute the sp_who2, get the blkby spid and run a dbcc inputbuffer. Hopefully the eventinfo will give you something a bit more tangible to go on.
sp_who2
DBCC INPUTBUFFER(62)
GO
Use a "Instance Per Request" strategy in your DI-instantiation code and your problem will be solved
Most probably you are using dependency injection. During web development you have to take into account the possibility of concurrent requests. Therefor you have to make sure every request gets new instances during DI, otherwise you will get into concurrency issues. Don't be cheap by using ".SingleInstance" for services and contexts.
Enabling MARS will probably decrease the number of errors, but the errors that are encountered will be less clear. Enabling MARS is always never the solution, do not use this unless you know what you're doing.

Automatic failover with SQL mirroring and connection strings

I have 3 servers set up for SQL mirroring and automatic failover using a witness server. This works as expected.
Now my application that connects to the database, seems to have a problem when a failover occurs - I need to manually intervene and change connection strings for it to connect again.
The best solution I've found so far involves using Failover Partner parameter of the connection string, however it's neither intuitive nor complete: Data Source="Mirror";Failover Partner="Principal" found here.
From the example in the blog above (scenario #3) when the first failover occurs, and principal (failover partner) is unavailable, data source is used instead (which is the new principal). If it fails again (and I only tried within a limited period), it then comes up with an error message. This happens because the connection string is cached, so until this is refreshed, it will keep coming out with an error (it seems connection string refreshes ~5 mins after it encounters an error). If after failover I swap data source and failover partner, I will have one more silent failover again.
Is there a way to achieve fully automatic failover for applications that use mirroring databases too (without ever seeing the error)?
I can see potential workarounds using custom scripts that would poll currently active database node name and adjust connection string accordingly, however it seems like an overkill at the moment.
Read the blog post here
http://blogs.msdn.com/b/spike/archive/2010/12/15/running-a-database-mirror-setup-with-the-sqlbrowser-service-off-may-produce-unexpected-results.aspx
It explains what is happening, the failover partner is actually being read from the sql server not from your config. Run the query in that post to find out what is actually being used as the failover server. It will probably be a machine name that is not discoverable from where your client is running.
You can clear the application pool in the case a failover has happened. Not very nice I know ;-)
// ClearAllPools resets (or empties) the connection pool.
// If there are connections in use at the time of the call,
// they are marked appropriately and will be discarded
// (instead of being returned to the pool) when Close is called on them.
System.Data.SqlClient.SqlConnection.ClearAllPools();
We use it when we change an underlying server via SQL Server alias, to enforce a "refresh" of the server name.
http://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqlconnection.clearallpools.aspx
The solution is to turn connection pooling off Pooling="false"
Whilst this has minimal impact on small applications, I haven't tested it with applications that receive hundreds of requests per minute (or more) and not sure what the implications are. Anyone care to comment?
Try this connectionString:
connectionString="Data Source=[MSSQLPrincipalServerIP,MSSQLPORT];Failover Partner=[MSSQLMirrorServerIP,MSSQLPORT];Initial Catalog=DatabaseName;Persist Security Info=True;User Id=userName; Password=userPassword.; Connection Timeout=15;"
If you are using .net development, you can try to use ObjAdoDBLib or PigSQLSrvLib and PigSQLSrvCoreLib, and the code will become simple.
Example code:
New object
ObjAdoDBLib
Me.ConnSQLSrv = New ConnSQLSrv(Me.DBSrv, Me.MirrDBSrv, Me.CurrDB, Me.DBUser, Me.DBPwd, Me.ProviderSQLSrv)
PigSQLSrvLib or PigSQLSrvCoreLib
Me.ConnSQLSrv = New ConnSQLSrv(Me.DBSrv, Me.MirrDBSrv, Me.CurrDB, Me.DBUser, Me.DBPwd)
Execute this method to automatically connect to the online database after the mirror database fails over.
Me.ConnSQLSrv.OpenOrKeepActive
For more information, see the relevant links.
https://www.nuget.org/packages/ObjAdoDBLib/
https://www.nuget.org/packages/PigSQLSrvLib/
https://www.nuget.org/packages/PigSQLSrvCoreLib/

Another ODBC Call Failed Topic

I am running Access 2010 FE and SQL Server 2005 BE.
I can execute pass through queries to my SQL Server succesfully by using DSNless connections.
During my testing phase sometimes I need to restore my database to get back to my original records so I can rerun my pass through queries. What I have found is when I run a pass through query, it creates an active connection on my SQL Server. I see the connection via the SQL Server Management Console under the MANAGEMENT | SQL Server Logs | Activity Monitor, select view processes. There I can see which process ID is being used and who is using it when I run my pass through query.
Now the only way for me to restore my database is to KILL the PROCESS e.g. Active connection
Now when I have my restored database in place and re-run the pass through query, I receive a ODBC -- Call Failed message box. I have attempted to run a procedure to refresh my querydefs but to no avail, I will still get the ODBC-- Call Failed message box when I click on those objects.
Now there are two options on how to fix this problem, which in either case I find not USER Friendly.
Restart my Access Application
Wait approx 5-10 minutes to rerun the Pass Through Query
I created a function to trap my ODBC Errors and this is what appears:
ODBC Error Number: 0
Error Description: [Microsoft][ODBC SQL Server Driver]Communication link failure
ODBC Error Number: 3146
Error Description: ODBC--call failed.
So if for some reason, I need to restart my SQL server or kill a process (Active Connection) on my SQL server while the Access Application is currently connected via ODBC, the objects created via ODBC will not perform properly till I execute the 2 workaround solutions as stated above.
Can anyone shed some advice on a solution? I appreciate any insight.
I asked a similar question some time ago, and never got a satisfactory answer. My original question is here: Force SET IDENTITY_INSERT to take effect faster from MS Access
There is a registry setting documented here for ACE that controls the timeout behavior:
ConnectionTimeout: The number of seconds a cached connection can remain idle before timing out. The default is 600 (values are of type REG_DWORD).
So as a third workaround (in addition to the two you already listed) you can change that registry setting to a shorter timeout (like 10 seconds). This is the approach I took in my answer. One caveat is that shortening the timeout may cause performance or other issues. Your mileage may vary.
See my full answer to the original question for more info.

Django how to reconnect after DatabaseError: query timeout

I have a stand-alone script that reads/writes from/to Postgre using Django ORM.
I get this error occasionally
DatabaseError: query timeout server
closed the connection unexpectedly
This probably means the server terminated abnormally
before or while processing the request.
I need to re-establish the connection and retry the processing code in the script, but can't seem to find a way. The following code raises 'InterfaceError: connection already closed' on retry, so it doesn't work.
for repeat in range(5):
try:
.....................PROCESSING CODE...................
except DatabaseError, e:
time.sleep(30)
else:
break
else:
return
Any idea?
I have a similar need for recreating the database connection and I'm trying the following black magic to reset the connection in django 1.3:
from django.db import connection
connection.connection.close()
connection.connection = None
I don't have PostgreSQL handy to try this out, but it seems to work for MySQL and sqlite at least. Also, if you're using multi-db, you're going to have to perform this step on your specific connection from the django.db.connections dictionary.

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