updating index

[no spam]

I have an index where I'm storing the primary key of my database record as
an unindexed field.   Nightly I want to update my search index with any
database changes / additions.

I don't really see an efficient way to update these records besides doing
something like this which I'm worried with thrash the index.  Is this
approach good/bad/ugly?

Thanks,
Mark

IndexReader reader;
ArrayList docsToUpdate;

for (int i = 0; i < reader.maxDoc(); i++)
{
   Document doc = reader.document(i);
   if (doc != null)
   {
      String prinaryKey = doc.getField("id");

       if (docsToUpdate.contains(primaryKey))
       {
            // set fields
            writer.updateDocument(doc);
       }
}

// for all docs not found in index
for (DBObject o : docsToUpdate)
{
   if (o.syncedWithIndex() == false)
   {
      // create new doc
     Document doc = ....;

      // this is a new doc
      writer.addDocument(doc);
   }
}