When I need to read millions of database rows from a PostgreSQL database using the JDBC driver, I always use a cursor, otherwise I will get an OutOfMemoryError. Here is the pattern (pseudocode) that I use:

```
begin transaction
execute("declare cursor...")
while (true) {
  boolean processedSomeRows = false
  resultSet = executeQuery("fetch forward...")
  while (resultSet.next()) {
    processedSomeRows = true
    ...
  }
  if (!processedSomeRows) break
}
close cursor
commit

```

This is a more "functional" equivalent that I came up with to be implemented in Scala:

```
begin transaction
execute("declare cursor...")

@tailrec
def loop(resultSet: ResultSet,
         processed: Boolean): Boolean = {
  if (!resultSet.next()) processed
  else {
    // Process current result set row
    loop(resultSet, true)
  }
}

while (loop(executeQuery("fetch forward..."), false))
  ; //Empty loop

close cursor
commit

```

I know this is contrived, but is there a better way without resorting to mutability? If I were trying to do this in Haskell, I might come up with a solution that involves monads, but I don't want to send my mind down those "twisty little passages, all alike," because it might never return...