Just wondering if anyone knows how to display the status of a DB connection on a page.
I would like to know if there is a good connection, or if it is down. In this case I would also display the reason.
While working with database with asp.net, you connection shouldn't be open all the time. Keeping in this mind you dont have to (and shouldnt) display connection status of database all the time. What you should do is while performing queries with ado.net or another OR/M just capture SqlExceptions and provide meaningfull errors to your user.
From msdn article :
try {
// code here
}
catch (SqlException odbcEx) {
// Handle more specific SqlException exception here.
}
catch (Exception ex) {
// Handle generic ones here.
}
Just capture the db exception, cause it will fire an exception/error once there is no connection.
and if there is a connection, you would know
There could be many ways to check for connection status, You may use ASP.Net Timer to periodically check for the connection, (remember that each timer interval causes a postback to the server and causes network traffic ), See Walkthrough: Using the ASP.NET Timer Control with Multiple UpdatePanel Controls
In the Timer_Tick event, you may check for the connection and post a message in label. Something on the following lines...
protected void Timer1_Tick(object sender, EventArgs e)
{
try
{
using (SqlConnection sqlConn =
new SqlConnection("YourConnectionString"))
{
sqlConn.Open();
Label1.Text = "Database Available";
}
}
catch (Exception ex)
{
Label1.Text = "Database Un-Available, " + "Possible Reason:"+ ex.Message;
}
}
Its not a good practice to catch generic exception (Exception) , you may catch SQLException and then have another block to handle generic exception.
Ideally, it is not really a good practice to tell users about database. Any database error should be logged and replaced with a more user friendly error message.
If you still need to display connection state on the screen, you can handle the StateChange event for SQLConnection and display appropriate message.
Update: I would suggest that you just log the errors and have a program to send you emails with failures or manually look into the system rather than users telling you that your database is down.
Related
I would like to detect connection state to MySql database. My database is deployed in different server than my app and there is good chances to lose connection to it via network. So I have to take this scenario into consideration.
Here is what I tried so far (a simplified test example):
static string connectionString = "***";
public static MySqlConnection Connection;
static System.Timers.Timer _timer;
static void _timer_Elapsed(object sender, ElapsedEventArgs e)
{
try
{
if (Connection.State != System.Data.ConnectionState.Open)
Connection.Open();
// Call method to invoke MySqlCommand.ExecuteNonQuery
mysqlCommand.ExecuteNonQuery();
}
catch (MySqlException ex)
{
Console.WriteLine("SQL EXCEPTION: " + ex);
// Handle all type of database exceptions
switch(ex.Number)
{...}
}
catch (Exception ex)
{
Console.WriteLine("OTHER EXCEPTION: " + ex);
}
}
static void Main(string[] args)
{
Connection = new MySqlConnection(connectionString);
_timer = new System.Timers.Timer(3000);
_timer.Elapsed += new ElapsedEventHandler(_timer_Elapsed);
_timer.Enabled = true;
Console.ReadKey();
}
If the connection to MySql is lost, I got a general exception:
IOException : Unable to write data to the transport connection: An
established connection was aborted by the software in your host
machine.
I was expecting MySqlException to be fired but that was not the case.
Also, if the connection to MySql is restored, I still get the IOException instead of executing the query. Seems like, MySqlConnection object has not been updated and it doesn't care about new connection state.
What's the best way to handle connection lost exception?
How can I refresh MySqlConnection when connection is restored?
Note: that I can't instantiate a new MySqlConnection object for each new query, because the program I'm trying to change has a Singleton of type MySqlConnection which is initialized only once. I know that's a bad design but I don't want to change this design now. I just want to catch connection lost exception and try to refresh MySqlConnection to continue to work correctly.
If your MySqlConnection instance loses its connection to your MySQL server, you cannot expect that instances's connection to be restored automatically or otherwise.
You need to try to reconnect with a new instance of MySqlConnection. The one that has lost the connection is now in a terminal state and cannot be reused.
To do this, I suppose you could do something like this
...
catch (MySqlException ex)
{
if (/*ex is a connection drop */) {
Connection?.Dispose();
Connection = new MySqlConnection(...);
Connection.ConnectionString = /* your connection string */;
Connection.Open();
}
else {
throw;
}
}
You are correct that your design has a flaw. Whether or not your flaw is fatal is hard to tell without testing.
These Connection instances are not thread safe or in any way reentrant. If you use one in a timer handler or thread, you may only use it in that context. Otherwise, if it's already in use when your timer or thread is invoked, things will get dicey. If you're lucky you'll get an exception. If you're less lucky your MySQL server will receive gibberish from your client and detect it. If you're even less lucky your data will get scrambled up.
ADO.NET and the MySqlConnection object implement connection pooling. This matters because it makes opening connections, using them, and then closing them, a lot cheaper than you might have expected.
Sometimes MySQL drops connections that your programs have held open for long periods of time. This post may help if that is your problem.
How can I change the default Mysql connection timeout when connecting through python?
When you lost your connection by networks problems, the connection object does not change Status property so evaluate it before executting commands doesn't work.
However, the database property (connection.database) goes to empty string so you can evaluate it so can close the connection an restores it:
oConn is an instance of MySQLConnection (it works on odbcconnection)
[VB.NET]
If Not IsNothing(oConn) Then
If (oConn.Database.Equals(String.Empty)) Then oConn.Close()
End If
[C#]
If (Not IsNothing(oConn)){
If (oConn.Database.Equals(String.Empty)) oConn.Close();
}
I have a windows application which executes some sql queries in a database. If we connect to a database and execute manually, we will be getting some message from sql server management studio(SSMS) either it may be success or failure. I want that message to be printed in my application message box. I googled and tried some code like:
string test = ((string)SqlCmd.ExecuteScalar());
MessageBox.Show(test);
But the result which is printed here is something else, which is not expected. I confirmed by executing the same step manually which shown me success message.
Can anyone please help me on this? Any comments would be really appreciated..
What you need to do is wrap the execution in a try catch block, and display the message if an exception occurs, otherwise, success.
Something like
try
{
SqlCmd.ExecuteScalar();
MessageBox.Show("Success");
}
catch(Exception ex)
{
MessageBox.Show(String.Format("An exception occurred : {0}", ex.Message);
}
The Exception class might be a bit generic, so you might wat to refine the catch block with multiple catches to manipulate the error message.
If it is not needed to use ExecuteScalar then I would suggest that you use one of the methods as explained here
I have a C# Console Application that is essentially a long batch process that processes data on a nightly basis across many different databases. What is the proper or preferred way to test basic database connectivity at the beginning of this type of program? I ran into the issue of having an expired database password for one of my connections that was caught by exception handling but I want to test for basic connectivity at the very beginning.
Would a simple SELECT query suffice or is there a more efficient way of doing this for numerous databases?
IMHO the simplest way is trying to connect to database and, if you have a failure, you give up.
As you're running a night batch, it's not important to understand immediately the reason and solve it.
So something like this
using(SqlConnection conn = new SqlConnection(connectionString))
{
try
{
conn.Open();
// Do what you please here
}
catch (Exception ex)
{
// Write error to file
File.Append(...,
DateTime.Now.ToString("yyyy-MM-dd hh:mm:ss") + " " +
ex.Message);
}
finally
{
conn.Close();
}
}
Next morning you can check file for errors...
'Connection.open`
is the simple way to determine if you can connect to db or not.
using (SqlConnection connection = new SqlConnection(connectionString))
{
connection.Open();
}
If you get a SqlException with number 18487 or 18488 it indicates the password has been changed.
Connection.changePassword
You don't need to run any query.
If you use SqlConnection passing the connection string, you can just try to Open() the connection and you'll get an exception if you cannot connect
Something like:
try
{
var cnn = new SqlConnection(connectionString);
cnn.Open();
}
catch
{
// connection failed, do something
}
Opening (and then closing) a connection should be sufficient to test the password. however, this does not tell you , if a db-user has permissions to access specific tables.
In my Windows application I try to connect to SQL Server 2008 with following code:
SqlConnection connection = new SqlConnection(Properties.Settings.Default.KargarBandarConnectionString);
SqlCommand command = new SqlCommand("Select IsAdmin from Users where UserName=#UserName And Password=#Password", connection);
SqlDataReader dataReader = null;
command.Parameters.AddWithValue("#UserName", UserNameTextBox.Text.Trim());
command.Parameters.AddWithValue("#Password", PasswordTextBox.Text);
try
{
connection.Open();
dataReader = command.ExecuteReader();
if (dataReader.HasRows)
{
while (dataReader.Read())
{
IsAdmin = dataReader.GetBoolean(0);
}
this.DialogResult = DialogResult.OK;
}
else
{
FMessageBox.ShowWarning("error");
UserNameTextBox.Focus();
}
}
catch (Exception ex)
{
if (progressForm != null)
progressForm.Close();
FMessageBox.ShowError(ex.Message);
}
finally
{
if (dataReader != null)
{
dataReader.Close();
dataReader.Dispose();
}
if (connection != null)
{
connection.Close();
connection.Dispose();
}
}
Everything works properly, but sometimes I get the following error:
timeout expired. the timeout period elapsed prior to obtaining a
connection from the pool ...
How can this be solved?
The reason you're getting this exception is because you have exhausted your connection pool and the number of "available" connections in your application.
Every time you open a connection, one is pulled from the connection pool if possible, or a new one is created if not.
However, to prevent galloping usage of connections, a limit of 100 (I think this is configurable) exists, and if you try to use more than 100 simultaneous connections, the code will not create new ones, and instead sit down to wait for one to be returned to the pool, and in this case you get a timeout if it sits too long.
So, for the particular example of code you've shown, I would:
Close the connection before I show an error messages to the user
However, unless 100 users are seeing the error message and leaving it there at the same time, it is unlikely the code you've shown is the cause of this problem.
Other than that, I would go through the entire application and ensure you don't have any connection leaks other places.
This particular type of exception can occur in one spot even though the problem is somewhere else. Example: A report is leaking an open connection every time it runs, and you run it 100 times successfully, then someone tries to log in, and the exception occurs in the login form.
That happens if you either:
leak connections (leaving them for GC to deal with rather than disposing them)
just have too much happening, such that the pool is exhausted
The first is the most common, and I expect it relates a lot to the fact that you are over-complication your error handling. This makes it easy to miss, and hard to spot that you've missed it. The code shown looks OK, but it would be far preferable to use using blocks for all the IDisposable elements, rather than finally. Also; don't keep the connection while you show modal things like the message box, unless you need the connection afterwards. Frankly, a lot of benefit here could be made by cleanly separating the UI and data-access code, then there is not temptation to stick a message-box in the middle of a database query.
However! To be explicit, I believe this code is the victim of some other code that is hogging connections. Look at your other data access code for the cause of this.
Refactor your code to look something like this. Implement using blocks. The other answers here are very important, be sure to understand them.
bool res=false;
try
{
using(var connection = new SqlConnection(Properties.Settings.Default.KargarBandarConnectionString))
using(var cmd = conn.CreateCommand())
{
cmd.commandText = "Select IsAdmin from Users where UserName=#UserName And HashedAndSaltedPassword=#PwdHash";
cmd.Parameters.AddWithValue("#UserName", UserNameTextBox.Text.Trim());
cmd.Parameters.AddWithValue("#PwdHash", SaltAndHash(PasswordTextBox.Text));
connection.Open();
var result = cmd.ExecuteScalar();
if (result!=null)
{
res=bool.Parse(result);
this.DialogResult = DialogResult.OK;
}
}
}
catch (Exception ex)
{
if (progressForm != null){progressForm.Close();}
FMessageBox.ShowError(ex.Message);
}
if(res==false)
{
FMessageBox.ShowWarning("error");
UserNameTextBox.Focus();
}
I one of my c# application, i have written sql connection code as following
try
{
myConnection = new SqlConnection(m_resourceDB.GetResourceString(nSiteID, ApplicationID.XClaim,(short)nResID ) );
myConnection.open();
}
I want to handle unkown issue of sqlserver like database down, time out.
For this i though to introduce for loop 3 times with 3 minute sleep between loop and if at all problem is there then i will exit from loop
I don't know my though is right or not? I want some expert advice on this? Any example?
I would say simply: the code that talks to connections etc should not be doing a sleep/retry, unless that code is already asynchronous. If the top-level calling code wants to catch an exception and set up a timer (not a sleep) and retry, then fine - but what you want to avoid is things like:
var data = dal.GetInfo();
suddenly taking 3 minutes. You might get away with it if it is an async/callback, and you have clearly advertised that this method may take minutes to execute. But even that feels like a stretch. And if you are up at the application logic, why not just catch the exception the first time, tell the user, and let the user click the button again at some point in the future?
If you are running a service with no user interface, then by all means, keep on looping until things start working, but at least log the errors to the EventLog while you're at it, so that the server admin can figure out when and why things go wrong.
For a client application, I would no suggest that you make the user wait 9 minutes before telling them things are not working like they should. Try to connect, assess the error condition, and let the user know what is going wrong so that they can take it further.
If you are using the SqlException class you can check the Exception Class and decide based on that what is going wrong, for example:
switch (sqlEx.Class)
{
case 20:
//server not found
case 11:
//database not found
All the classes have the SQL Server message on them, it is a matter of testing the different conditions.
It really depends on how you want your application to behave.
If your database access is dealt with on the same thread as your UI then whilst you are attempting to connect to a database it will become unresponsive.
The default time period for a connection timeout is already pretty long and so running it in a for loop 3 times would triple that and leave you with frustrated users.
In my opinion unless your specifically attempting to hide connection issues from the user, it is by far better to report back that a connection attempt has failed and ask the user if they wish to retry. Then having a count on the number of times that you'll allow a reconnection attempt before informing the user that they can't continue or putting the application into an "out of service" state.
I want to handle unkown issue of sqlserver like database down, time out.
Try to surround connection operation with using statement to capture connection related problems .
using( sqlcon = new SqlConnection(constr))
{}
Use the Try/Catch Statement for capturing the exception:
try
{
con.Open();
try
{
//Execute Queries
// ....
}
catch
{
// command related or other exception
}
finally
{
con.Close();
}
}
catch
{
// connection error
}
To prevent Exception of such type check these:
Troubleshooting Timeout SqlExceptions
you can set the CommandTimeout to some value on a SqlCommand:
objCmd.CommandTimeout = 600
You can catch the SqlException.
SqlException.Class
Gets the severity level of the error returned from the .NET Framework Data Provider for SQL Server.
SqlException.Errors
Gets a collection of one or more SqlError objects that give detailed information about exceptions generated by the .NET Framework Data Provider for SQL Server.
SqlCommand cmd = new SqlCommand();
cmd.Connection = new SqlConnection("CONNECTION_STRING");
cmd.CommandText = "SELECT * FROM ....";
// cmd.CommandType = System.Data.CommandType.Text;
try
{
cmd.Connection.Open();
try
{
SqlDataReader reader = cmd.ExecuteReader();
// ....
}
finally
{
cmd.Connection.Close();
}
}
catch (SqlException ex)
{
// ex.Class contains the ErrorCode, depends on your dataprovider
foreach (SqlError error in ex.Errors)
{
// error.LineNumber
// error.Message
}
}
The best way would be to putt it in a try catch statement and display the error in a better format, If it fails for 1 time, trying it continue sly 3 times will not change anything untill and unless you dc and send request again, In a separate in separate packed as a new request.
use try this.
try
{
Executing code.
}
catch (Exception err)
{
Display["ErrorMsg"] = err.Message.ToString() + "|" + err.GetBaseException() + "|" + Request.Url.ToString();
}
Good Luck.