We have had the same thing happening with failed Oracle connections. If I remember well, it happened when the correct Oracle client wasn't found or when the tns-name wasn't found. Could also be a timeout having caused the problem.

So yes, we've also seen disks completely filling up with dump files. What we do now, is delete them all when starting the application:

// v1, mjl, 18/03/19: delete "*_minidump_default_pid_*.*" files:
n_cst_dirattrib lnv_dirAttribs[]
n_cst_filesrv lnv_filesrv
long ll_fileCnt, ll_i
lnv_filesrv = create n_cst_filesrvunicode
ll_fileCnt = lnv_filesrv.of_dirlist( of_getappdir() + "\*_minidump_default_pid_*.dmp", 0 + 32, lnv_dirAttribs )
//messagebox('debug', of_getappdir() )
for ll_i = 1 to ll_fileCnt
	setpointer(hourglass!)
	try 
		fileDelete( of_getappdir() + "\" + lnv_dirAttribs[ll_i].is_filename )
	catch ( runtimeerror rt)
		// simply don't want to see any errors, hence the try catch
	end try
next
//if ll_fileCnt > 0 then
//	Messagebox("Information", string(ll_fileCnt) + " dump files have been deleted", information!)
//end if
setpointer(hourglass!)
destroy lnv_filesrv

regards,

MiguelL

This doesn't look like it's only a PB problem.

https://dba.stackexchange.com/questions/198468/how-can-i-prevent-oracle-to-create-minidumps

https://community.appeon.com/index.php/qna/q-a/what-is-this-dmp-file

Search for _minidump_default_pid at google and you'll find plenty more questions about it. One of the results indicates a newer version of the Oracle driver might solve it. 
https://superuser.com/questions/438315/process-keeps-creating-dump-files

There are also suggestions on hiding the problem (settings where it won't generate the dmp file), but that's sub-optimal in that an actual problem might not get reported too.