Database Transactions in Xojo

Every now and then someone on the Xojo forum wonders why inserting data into an SQLite database is so slow.  Databases are designed to hold billions of records and do it fast, right?  So why is their application so slow?  The answer is they are relying upon the built-in transaction in Xojo.

By default SQLite databases do an automatic transaction for you.  This means that as soon as you attempt to insert, update, or delete data the work to write that change to disk happens as soon as possible.

For example, let’s take the following bit of code to insert data into a table:

For i As Integer = 1 To kMax
   Dim dbr As New DatabaseRecord
   dbr.Column("Name") = GetName
   dbr.IntegerColumn("Age") = GetAge
   dbr.DateColumn("TheDate") = New date
   db.InsertRecord "t_table", dbr
   If db.Error Then
      MsgBox "DB Error: " + db.ErrorMessage
      Return
   End
Next

GetName gets a random name from an array that has 26 names in it and adds a random integer between 1000 and 10000.  GetAge returns a random integer between 1 and 74. 

This is pretty simple insert and if you run this 10,000 times it takes roughly 49 seconds saving to a desktop SQLite file on my 5k iMac.  And in so doing the application is locked up for that entire time because I’m in the tight loop.  This is simply unacceptable.

I’m sure someone is screaming why are you using the DatabaseRecord!  It’s slow!  It’s inefficient!  You should be using PreparedStatement’s!  Okay, so using pretty much the same logic:

Dim sql As String = "Insert into t_table (Name, Age, TheDate) Values(?, ?, ?);"
Dim ps As SQLitePreparedStatement = db.Prepare(sql)
ps.BindType(0, SQLitePreparedStatement.SQLITE_TEXT)
ps.BindType(1, SQLitePreparedStatement.SQLITE_INTEGER)
ps.BindType(2, SQLitePreparedStatement.SQLITE_TEXT)
For i As Integer = 1 To kMax
   ps.Bind(0, GetName)
   ps.bind(1, GetAge)
   ps.Bind(2, New Date)
   ps.SQLExecute
   If db.Error Then
      MsgBox "DB Error: " + db.ErrorMessage
      Return
   End
Next

This takes about 48 seconds.  No big time savings there.  Obviously that’s not the improvement we need.

What we need to do is put these inserts in a database transaction using the following bit of code before the loop starts:

db.SQLExecute("BEGIN TRANSACTION")
If db.Error Then
   MsgBox "DB Error: " + db.ErrorMessage
   Return
End

And then at the end use:

db.Commit

Using the DatabaseRecord method takes a whopping 1 second with 10,000 records.  Using the prepared statement is so fast that my measured elapsed time in seconds is effectively 0.  

If I up the number of records inserted to 1,000,000 I get an interesting result.  The DatabaseRecord method takes 27 seconds where the PreparedStatement method takes 47 seconds.  And if I declare the PreparedStatement inside the loop it now takes 55 seconds.

What have we learned in this blog post?  First, using a database transaction is considerably faster than using the default transaction behavior.  Second, using DatabaseRecord is pretty fast and depending upon the number of record inserted it might be considerably faster.  Honestly, I didn’t expect this.  

In the next blog post I’ll look at Record updates and what are the best methods.