Trying to delete one big database activity, breaks with memory exhausted problem.

Looking at code, it seems that data_delete_instance() is highly inefficient:

1) It uses one get_records() instead of get_recordset()
2) It instantiated one object for each field and for each record.
3) It uses the delete_content_files() but params doesn't match at all, so I guess it isn't deleting the files at all

I would suggest to:

• Take a look to the code in data_delete_instance() under 2.0.
• For the DB part, backport it for 1.9. It's simple and quick
• For the "potential" files, avoid the delete_content_files() completely and go and delete recursively the directory:
  • $CFG->dataroot.'/'.COURSEID.'/'.$CFG->moddata.'/data/'. DATAID

That way there won't be more problems deleting one data instance completely, IMO.