Question

I’m getting locking exceptions when trying to use transactions with SubSonic and SQLite. I’m using this from a single thread and there are no other processes accessing my db, so I really didn’t expect any such problems.

If I write code like this below, I get an exception on the second call to Save() within the loop – so the third call to Save() over all.

       using (TransactionScope ts = new TransactionScope())
       {
            using (SharedDbConnectionScope sharedConnectinScope = new SharedDbConnectionScope())
            { 
                SomeDALObject x = new SomeDALObject()
                x.Property1 = "blah";
                x.Property2 = "blah blah";
                x.Save();

                foreach (KeyValuePair<string, string> attribute in attributes)
                { 
                    AnotherDALObject y = new AnotherDALObject()
                    y.Property1 = attribute.Key
                    y.Property2 = attribute.Value
               
                    y.Save();  // this is where the exception is raised, on the 2nd time through this loop
                }
            }
       }

If I have the using() statements as above, or if I just have using (TransactionScope ts = new TransactionScope()) then I get a System.Data.SQLite.SQLiteException with message

The database file is locked

database is locked

The stack trace is:

   at System.Data.SQLite.SQLite3.Step(SQLiteStatement stmt)
   at System.Data.SQLite.SQLiteDataReader.NextResult()
   at System.Data.SQLite.SQLiteDataReader..ctor(SQLiteCommand cmd, CommandBehavior behave)
   at System.Data.SQLite.SQLiteCommand.ExecuteReader(CommandBehavior behavior)
   at System.Data.SQLite.SQLiteCommand.ExecuteNonQuery()
   at System.Data.SQLite.SQLiteTransaction..ctor(SQLiteConnection connection, Boolean deferredLock)
   at System.Data.SQLite.SQLiteConnection.BeginDbTransaction(IsolationLevel isolationLevel)
   at System.Data.SQLite.SQLiteConnection.BeginTransaction()
   at System.Data.SQLite.SQLiteEnlistment..ctor(SQLiteConnection cnn, Transaction scope)
   at System.Data.SQLite.SQLiteConnection.EnlistTransaction(Transaction transaction)
   at System.Data.SQLite.SQLiteConnection.Open()
   at SubSonic.SQLiteDataProvider.CreateConnection(String newConnectionString)
   at SubSonic.SQLiteDataProvider.CreateConnection()
   at SubSonic.SQLiteDataProvider.ExecuteScalar(QueryCommand qry)
   at SubSonic.DataService.ExecuteScalar(QueryCommand cmd)
   at SubSonic.ActiveRecord`1.Save(String userName)
   at SubSonic.ActiveRecord`1.Save()
   at (my line of code above).

If I have the using statments nested the other way around, with SharedDbConnectionScope on the outside, then I get a TransactionException with message "The operation is not valid for the state of the transaction." Stack trace is:

at System.Transactions.TransactionState.EnlistVolatile(InternalTransaction tx, IEnlistmentNotification enlistmentNotification, EnlistmentOptions enlistmentOptions, Transaction atomicTransaction)
   at System.Transactions.Transaction.EnlistVolatile(IEnlistmentNotification enlistmentNotification, EnlistmentOptions enlistmentOptions)
   at System.Data.SQLite.SQLiteEnlistment..ctor(SQLiteConnection cnn, Transaction scope)
   at System.Data.SQLite.SQLiteConnection.EnlistTransaction(Transaction transaction)
   at System.Data.SQLite.SQLiteConnection.Open()
   at SubSonic.SQLiteDataProvider.CreateConnection(String newConnectionString)
   at SubSonic.SQLiteDataProvider.CreateConnection()
   at SubSonic.SQLiteDataProvider.ExecuteScalar(QueryCommand qry)
   at SubSonic.DataService.ExecuteScalar(QueryCommand cmd)
   at SubSonic.ActiveRecord`1.Save(String userName)
   at SubSonic.ActiveRecord`1.Save()
   at (my line of code above)

and the inner exception is "Transaction Timeout"

I don’t have any custom code in my generated DAL classes, or anything else clever that I can think of that would be causing this.

Anyone else encountered transaction problems like this or can someone suggest where I start looking for the problem?

thanks!

UPDATE: I notice mention of transaction-related things in the release notes for versions 1.0.61-65 (e.g. here), so perhaps updating SubSonic to work with the latest version of the .Net Data Provider would solve some of these issues…

Answer 1

In doing the revised sqlite provider for subsonic 2.x I created a full set of unit tests based on the existing subsonic sqlserver tests. (These tests were also checked in with the revised code.) The only tests that failed were the ones related to transactions (maybe the migration ones too). “The database file is locked” error message, as you have seen. Subsonic was written mainly for sql server that doesn’t do file level locking like SQLIte does, so some things don’t work; it would need to be rewritten to handle this better.

I have never used the TransactionScope as you have. I do my subsonic 2.2 transactions like this, and so far no problems with the SQLite provider. I can confirm that you need to use transactions with SQLite if dealing with multiple rows or it’s really slow.

public void DeleteStuff(List<Stuff> piaRemoves)
{
    QueryCommandCollection qcc = new QueryCommandCollection();

    foreach(Stuff item in piaRemoves)
    {
        Query qry1 = new Query(Stuff.Schema);
        qry1.QueryType = QueryType.Delete;
        qry1.AddWhere(Stuff.Columns.ItemID, item.ItemID);
        qry1.AddWhere(Stuff.Columns.ColumnID, item.ColumnID);
        qry1.AddWhere(Stuff.Columns.ParentID, item.ParentID);
        QueryCommand cmd = qry1.BuildDeleteCommand();
        qcc.Add(cmd);
    }
    DataService.ExecuteTransaction(qcc);
}