I'm using the following code to work out the next unique Order Number in an access database. ServerDB is a "System.Data.OleDb.OleDbConnection"
Dim command As New OleDb.OleDbCommand("", serverDB)
command.CommandText = "SELECT max (ORDERNO) FROM WORKORDR"
iOrder = command.ExecuteScalar()
NewOrderNo = (iOrder + 1)
If I subsequently create a WORKORDR (using a different DB connection), the code will not pick up the new "next order number."
e.g.
iFoo = NewOrderNo
CreateNewWorkOrderWithNumber(iFoo)
iFoo2 = NewOrderNo
will return the same value to both iFoo and iFoo2.
If I Close and then reopen serverDB, as part of the "NewOrderNo" function, then it works. iFoo and iFoo2 will be correct.
Is there any way to force a "System.Data.OleDb.OleDbConnection" to refresh the database in this situation without closing and reopening the connection.
e.g. Is there anything equivalent to serverdb.refresh or serverdb.FlushCache
How I create the order.
I wondered if this could be caused by not updating my transactions after creating the order. I'm using an XSD for the order creation, and the code I use to create the record is ...
Sub CreateNewWorkOrderWithNumber(ByVal iNewOrder As Integer)
Dim OrderDS As New CNC
Dim OrderAdapter As New CNCTableAdapters.WORKORDRTableAdapter
Dim NewWorkOrder As CNC.WORKORDRRow = OrderDS.WORKORDR.NewWORKORDRRow
NewWorkOrder.ORDERNO = iNewOrder
NewWorkOrder.name = "lots of fields filled in here."
OrderDS.WORKORDR.AddWORKORDRRow(NewWorkOrder)
OrderAdapter.Update(NewWorkOrder)
OrderDS.AcceptChanges()
End Sub
From MSDN
Microsoft Jet has a read-cache that is
updated every PageTimeout milliseconds
(default is 5000ms = 5 seconds). It
also has a lazy-write mechanism that
operates on a separate thread to main
processing and thus writes changes to
disk asynchronously. These two
mechanisms help boost performance, but
in certain situations that require
high concurrency, they may create
problems.
If you possibly can, just use one connection.
Back in VB6 you could force the connection to refresh itself using ADO. I don't know whether it's possible with VB.NET. My Google-fu seems to be weak today.
You can change the PageTimeout value in the registry but that will affect all programs on the computer that use the Jet engine (i.e. programmatic use of Access databases)
I always throw away a Connection Object after I used it. Due to Connection Pooling getting a new Connection is cheap.
Related
I am using the function getgroup() to read all of the groups of a user in the active directory.
I'm not sure if I'm doing something wrong but it is very very slow. Each time it arrives at this point, it takes several seconds. I'm also accessing the rest of Active directory using the integrated function of "Accountmanagement" and it executes instantly.
Here's the code:
For y As Integer = 0 To AccountCount - 1
Dim UserGroupArray As PrincipalSearchResult(Of Principal) = UserResult(y).GetGroups()
UserInfoGroup(y) = New String(UserGroupArray.Count - 1) {}
For i As Integer = 0 To UserGroupArray.Count - 1
UserInfoGroup(y)(i) = UserGroupArray(i).ToString()
Next
Next
Later on...:
AccountChecker_Listview.Groups.Add(New ListViewGroup(Items(y, 0), HorizontalAlignment.Left))
For i As Integer = 0 To UserInfoGroup(y).Count - 1
AccountChecker_Listview.Items.Add(UserInfoGroup(y)(i)).Group = AccountChecker_Listview.Groups(y)
Next
Item(,) contains my normal Active directory data that I display Item(y, 0) contain the username.
y is the number of user accounts in AD. I also have some other code for the other information in this loop but it's not the issue here.
Anyone know how to make this goes faster or if there is another solution?
I'd recommend trying to find out where the time is spent. One option is to use a profiler, either the one built into Visual Studio or a third-party profiler like Redgate's Ants Profiler or the Yourkit .Net Profiler.
Another is to trace the time taken using the System.Diagnostics.Stopwatch class and use the results to guide your optimization efforts. For example time the function that retrieves data from Active Directory and separately time the function that populates the view to narrow down where the bottleneck is.
If the bottleneck is in the Active Directory lookup you may want to consider running the operation asynchronously so that the window is not blocked and populates as new data is retrieved. If it's in the listview you may want to consider for example inserting the data in a batch operation.
I have a SQLite database that I want to lock for synchronization purposes. I don't want a process that runs async on a different box processing data that has been added from a different box until it has finished with updates. DataAccess is a class that connects to sPackageFileName and reuses the same connection as long as sPackageFileName is the same or unless .Close method is called. So basically DataAccess.ExecCommand executes a command.
In Google I found this ....
DataAccess.ExecCommand("PRAGMA locking_mode = EXCLUSIVE", sPackageFileName)
DataAccess.ExecCommand("BEGIN EXCLUSIVE", sPackageFileName)
DataAccess.ExecCommand("COMMIT", sPackageFileName)
This works as advertise. If I run this on box A and then on box B I get a "database locked" exception. The problem is how long it takes. I found a PRAGMA busy_timeout. This PRAGMA is timeout controls access locks, not database locks. I am stratring to think there is not PRAGMA for database lock timeout. Right now it seems about 3-4 minutes. One other note, the sPackageFileName is not on either box, they (box A and B) connect to it over a share drive.
Also I am using the VB.NET wrapper for the SQLite dll.
CL got me on the right trail. It was the timeout of the .NET command. Here the code setting it up from my class.
Dim con As DbConnection = OpenDb(DatabaseName, StoreNumber, ShareExclusive, ExtType)
Dim cmd As DbCommand = con.CreateCommand()
If _QueryTimeOut > -1 Then cmd.CommandTimeout = _QueryTimeOut
Don't get hang up on the variables, the purpose of posting the code is show I could show the property I was talking about. The default _QueryTimeOut was set the 300 (seconds). I set cmd.ComandTimeout to 1 (second) and it returned as expected.
As CL finally got through to me, the timeout was happening someplace else. Sometimes it takes a kick to get you out of the box. :-)
I'm using hsqldb to create cached tables and indexed tables.
The data being stored has pretty high frequency so I need to use a connection pool.
Also because there is a lot of data I do not call checkpoint on every commit, but rather expect the data to be flushed after 50,000 rows are inserted.
So the thing is that I can see the .data file is growing but when I connect with hsqldb client I don't see the tables and the data.
So I had 2 simple tests, one inserted single row and one inserted 60,000 rows to new table. In both cases I couldn't see the result in any hsqldb client.
(Note that I use shutdown=true)
So when I add checkpoint after each commit, it solve the problem.
Also if specify in the connection string to use log, it solves the problem (I don't want the log in production though). Also not using pooled connection solved the problem and last is using pooled data source and explicitly close it before shutdown.
So I guess that some connections in the connection pool are not being closed, preventing from the db to somehow commit the changes and make them available for the client. But then, why couldn't I see the result even with 60,000 rows?
I also would expect the pool to be closed automatically...
What am I doing wrong? What is happening behind the scene?
The code to get the data source looks like this:
Class.forName("org.hsqldb.jdbcDriver");
String url = "jdbc:hsqldb:" + m_dbRoot + dbName + "/db" + ";hsqldb.log_data=false;shutdown=true;hsqldb.nio_data_file=false";
ConnectionFactory connectionFactory = new DriverManagerConnectionFactory(url, user, password);
GenericObjectPool connectionPool = new GenericObjectPool();
KeyedObjectPoolFactory stmtPool = new GenericKeyedObjectPoolFactory(null);
new PoolableConnectionFactory(connectionFactory, connectionPool, stmtPool, null, false, true);
DataSource ds = new PoolingDataSource(connectionPool);
And I'm using this Pooled data source to create table:
Connection c = m_dataSource.getConnection();
Statement st = c.createStatement();
String script = String.format("CREATE CACHED TABLE IF NOT EXISTS %s (id %s NOT NULL, entity %s NOT NULL, PRIMARY KEY (id));", m_tableName, m_idGenerator.getIdType(), TABLE_ENTITY_TYPE);
st.execute(script);
c.close;
st.close();
And insert rows:
Connection c = m_dataSource.getConnection();
c.setAutoCommit(false);
Statement stmt = c.prepareStatement(m_sqlInsert);
stmt.setObject(1, id);
stmt.setBinaryStream(2, Serializer.Helper.serialize(m_serializer, entity));
stmt.executeUpdate();
stmt.close();
stmt = null;
c.commit();
c.close();
stmt.close();
so the above seems to add data but it cannot be seen.
When I explicitly called
connectionPool.close();
Then and only then I could see the result.
I also tried to use JDBCDataSource and it worked as well.
So what is going on? And what is the right way to do this?
Your method of accessing the database from outside your application process is simply wrong.
Only one java process is supposed to connect to the file: database.
In order to achieve your aim, launch an HSQLDB server within your application, using exactly the same JDBC URL. Then connect to this server from the external client.
See the Guide:
http://www.hsqldb.org/doc/2.0/guide/listeners-chapt.html#lsc_app_start
Update: The OP commented that the external client was used after the application had stopped. Because you have turned the log off with hsqldb.log_data=false, nothing is persisted permanently. You need to perform an explicit CHECKPOINT or SHUTDOWN when your application completes its work. You cannot rely on shutdown=true at all, even without connection pooling.
See the Guide:
http://www.hsqldb.org/doc/2.0/guide/deployment-chapt.html#dec_bulk_operations
I'm developing a piece of a system that basically migrates data from one set of tables to another set. Everything works fine, but I've decided to employ transactions instead of just failing on things that are partially completed. (That is, if some exception occurs, I want to rollback instead of having partial data migrated.)
I have a service (in the 3-tier architecture way, not web) which begins a transaction on the data access layer. The data context is shared in the data access class which contains many methods. Those methods use various LINQ-to-SQL techniques to update/insert/delete. All the LINQ-to-SQL "selects" are within CompiledQueries.
The "BeginTransaction" method starts a transaction like this:
Public Sub BeginTransaction() Implements ITransactionalQueriesBase.BeginTransaction
Me.Context.Connection.Open()
Me.Context.Transaction = Context.Connection.BeginTransaction()
IsInTransaction = True
End Sub
Basically, I have written a test which starts a transaction, inserts into a table, and then attempts to retrieve the value that was just inserted, all during the transaction. I did this because I wanted to assert that the insert method actually tries to insert. Then, during the test I would rollback, then test to ensure that the newly inserted value is not actually committed to the table. The test looks something like this:
<TestMethod()>
Public Sub FacilityService_Can_Rollback_A_Transaction()
faciService.BeginTransaction()
Dim devApp = UnitTestHelper.CreateDevelopmentApplication(devService.GetDevelopmentType("NEWFACI").ID, 1, 1, 1, 1)
Dim devInsertRes = devService.InsertDevelopmentApplication(devApp)
Assert.IsTrue(devInsertRes.ReturnValue > 0)
For Each dir1 In devInsertRes.Messages
Assert.Fail(dir1)
Next
Dim migrationResult = faciService.ProcessNewFacilityDevelopment(devInsertRes.ReturnValue)
Assert.IsTrue(migrationResult.ReturnValue.InsertResult)
Dim faciRetrieval1 = faciService.GetFacilityByID(migrationResult.ReturnValue.FacilityID)
Assert.IsNotNull(faciRetrieval1.ReturnValue)
faciService.Rollback()
Dim faciRetrieval2 = faciService.GetFacilityByID(migrationResult.ReturnValue.FacilityID)
Assert.IsNull(faciRetrieval2.ReturnValue)
End Sub
So, to my problem...
When the test gets to the "faciRetrieval1" step, it stays there for about 30-60 seconds before moving on. I'm not sure why this is happening. If I run the same queries in a transaction within SSMS it happens instantly. Does anyone have any ideas? The database is a SQL Server 2008 SP1 (R2?).
I figured out that if you have a data context using a transaction, any other data context appears to not be able to select from another context of the same type.
I ended up fixing it by using the same context throughout every select/update/delete while a transaction was happening.
I'm encountering a hang when the program tries to access the fruit database. I've already enabled network access MSDTC on both my development computer and the SQL Server server.
Code:
(pardon the code coloring...SO's misinterpreting my VB .NET)
Using ts As New TransactionScope
Dim fruit As New FruitDataContext
Dim thingies As New ThingiesDataContext
If (From f In fruit.tblApples Where f.Rotten = "Yes" AndAlso f.batch = 1).Count >= 1 Then
'Record today's date as the day that the rotten apples were dumped.
End If
'Other complicated code that uses ThingiesDataContext and FruitDataContext
du.SubmitChanges()
ts.Complete()
End Using
Edit:
I've dug around a bit more and it turns out that the problem lies in the line of LINQ. When I tried to view it with the LINQ to SQL Visualizer, I get the following error:
System.InvalidCastException: Specified cast is not valid.
at LinqToSqlQueryVisualizer.SqlQueryInfo.deserialize(Stream stream)
at LinqToSqlQueryVisualizer.Visualizer.Display(IDialogVisualizerService windowService, Stream rawStream)
at LinqToSqlQueryVisualizer.DialogChooser.Show(IDialogVisualizerService windowService, IVisualizerObjectProvider objectProvider)
at Microsoft.VisualStudio.DebuggerVisualizers.DebugViewerShim.ManagedShim.DelegatedHost.CreateViewer(IntPtr hwnd, HostServicesHelper hsh, SafeProxyWrapper proxy)
I've also edited the LINQ statement to be closer to my real code.
Final edit:
I tried using a normal SqlConnection instead of a "thingies as New ThingiesDataContext" and the problem still occurs.
It appears that TransactionScope cannot handle multiple SQL connections inside the same transaction.
Official Microsoft Note
parallel transactions are not supported by SQL Server.
From MSDN: http://msdn.microsoft.com/en-us/library/bb896149.aspx
This is not an MSDTC issue. If it were, you would get an error saying DTC is not enabled and needs to be. It's also not a deadlock issue, because you would get a specific error about that as well.
If I had to guess, I would say that the 'Other complicated code...' is attempting to perform a database operation and is being blocked by one or the other database context objects.
One way you can determine this is to run SQL Profiler to see what SQL statements are actually being executed on the server, and check for blocks.