| isfd | isam file descriptor |
| key | description of secondary index to delete, see isam indexes |
ISTRUE, or ISFALSE, in which case the error code is returned by isErrno, or found in isfd->iserrno
when deleting an index from a populated file, isDelIndex will purge the accumulated keys. in the case of larger files this could take a while, but will be significantly faster than the isAddIndex call.
if the file is not exclusively locked, an automatic ISEXCLLOCK will be placed around the operation, and if this is not possible, an ENOTEXCL error will be returned.