We did test your case. Firstly, we insert 300k records into the database, the records in the database look like the screenshot “dbrecrod.png” (attached). Then we use the following same code as yours to import data:
Workbook wb = new Workbook();
Cells cells = wb.getWorksheets().get(0).getCells();
long t = System.currentTimeMillis();
cells.importResultSet(rs, “A1”, true);
System.out.println(System.currentTimeMillis() - t);
The output time is 6378, that is, importing only takes about 6 seconds.
We are afraid we could not reproduce the performance issue. If you still think it is an issue of our component, please provide us your console application (runnable) and sample db data (such as, one sqlite database file) to reproduce the issue so we can make further investigation.