be protected from being deleted while any externally stored columns are
being fetched.

row_ext_create(),
row_upd_index_replace_new_col_vals(),
row_upd_index_replace_new_col_vals_index_pos(),
row_sel_sec_rec_is_for_blob(),
row_sel_sec_rec_is_for_clust_rec(): Note that the clustered
index record must be covered by a lock or a page latch.

row_upd_sec_index_entry(), row_upd_clust_rec_by_insert(),
row_undo_mod_upd_exist_sec(): Note that these functions probably
do not obtain an appropriate lock on the clustered index record
before fetching any externally stored columns.