Versions of 4D previous to 4D v11 SQL recommended that you turn indexes off before importing large amounts of information, then turn them back on after. This operation was necessary to completely rebuild the indexes.
In 4D v11 SQL, a new option has been added to the Import window. It is labeled "Rebuild indexes after import". It will automatically perform the re-indexing operation for you. It is highly recommended to leave this option checked, since importing large amounts of data with the index turned on is much slower.