similar 4.7.x-1.x-dev

Important upgrade note! If you added the fulltext index to the node table in your Drupal 4.6 setup, you MUST drop the index before performing your Drupal 4.7 upgrade, or the upgrade will fail: ALTER TABLE node DROP INDEX title.

If you also disable the similar module before performing the upgrade from 4.6 to 4.7 and manually execute the aforesaid index drop, the similar entries module install file, on a Drupal 4.7 site, should automatically create the new index for you on the node_revisions table.