Trying to delete a large database (more than 3000 records of 20 fields i.e.) crash with error
PHP Fatal error: Allowed memory size of 100663296 bytes exhausted (tried to allocate 71 bytes) in docs/lib/adodb/adodb.inc.php on line 3008

This happen because the delete function try to do a full left join before deleting all the entries.
You can find my solution in attachment, where all the entries are deleted using the minimal memory needed to do the job, and an explicit printout of the operation is done to get the client web page responsive during the long operations.

The attachment contains ONLY the function data_delete_instance modified, to be substituted in docs/mod/data/lib.php

sincerely yours.