Transactions in multi threaded environment in SQLite WP 8.1 - multithreading

Question

I am facing an issue using SQLite with following scenario.
There are two threads working on database.
Both threads have to insert messages in transactions.
So if say one thread commits after inserting 20k rows and other thread has not committed yet.
In output I see all the data has been committed which was inserted by thread 2 till the moment data was committed by thread 1.
Sample function:
/// <summary>
/// Inserts list of messages in message table
/// </summary>
/// <param name="listMessages"></param>
/// <returns></returns>
public bool InsertMessages(IList<MessageBase> listMessages, bool commitTransaction)
{
bool success = false;
if (listMessages == null || listMessages.Count == 0)
return success;
DatabaseHelper.BeginTransaction(_sqlLiteConnection);
foreach (MessageBase message in listMessages)
{
using (var statement = _sqlLiteConnection.Prepare(_insertMessageQuery))
{
BindMessageData(message, statement);
SQLiteResult result = statement.Step();
success = result == SQLiteResult.DONE;
if (success)
{
Debug.WriteLine("Message inserted suucessfully,messageId:{0}, message:{1}", message.Id, message.Message);
}
else
{
Debug.WriteLine("Message failed,Result:{0}, message:{1}", result, message.Message);
}
}
}
if (commitTransaction)
{
Debug.WriteLine("Data committed");
DatabaseHelper.CommitTransaction(_sqlLiteConnection);
}
else
{
Debug.WriteLine("Data not committed");
}
return success;
}
Is there any way to prevent commit transaction of thread 2 inserts?

Answer 1

In short, it's not possible on a single database.
A single sqlite database cannot have multiple simultaneous writers with separate transaction contexts. sqlite databases also do not have separate contexts per connection; to get a context, you would need to make a new connection. However, as soon as you start the initial write using insert (or update/delete), the transaction needs a RESERVED lock on the database (readers allowed, no other writers), which means parallel writes are impossible. I thought you might be able to fake it with SAVEPOINT and RELEASE, but these are also serialized on the connection and do not generate a separate context.
With that in mind, you may be able to use separate databases connected using ATTACH DATABASE, as long as both threads are not writing to the same table. To do so, you would attach the additional database at runtime which contains the other tables. However, you still need a separate connection for each parallel writer because commits to the connection still apply to all open transactions.
Otherwise, you can get separate transactions by opening an additional connection and the later connection & transaction will just have to wait until the RESERVED lock is released.
References:
SQLite Transactions
SQLite Locking
SQLite ATTACH DATABASE