Performance issue on import - chatty database communication

Hi,

I am importing CSVs with 10k rows and I noticed that it is very very slow. Like 10minutes to import more or less. This is against a django app running in my local connected to a postgres running in my local as well.

Upon further inspection, looks like for every row in the imported CSV, a select * from table where id = ? is performed, thereby slowing down the import. It may be better to do a select * from table where id in (?, ?, ?, ...) instead to speed up the process.

Thanks

[franz-see]

@andrewgy8 This is my workaround

class BulkQueryMixin:
    _ids_to_objects = {}

    def before_import(self, dataset, using_transactions, dry_run, **kwargs):
        if len(dataset):
            header_indices = [idx for idx, header in enumerate(dataset.headers) if header in self._meta.import_id_fields]
            query_ids = [[(dataset.headers[header_idx], data[header_idx],) for header_idx in header_indices] for data in dataset]
            where_clause = ' or '.join(['(%s)' % ' and '.join([self._to_where_condition(value[0], value[1]) for value in query_id])for query_id in query_ids])
            select_query = 'select * from %s where %s' % (self._meta.model._meta.db_table, where_clause)
            pre_queried_objects = self._meta.model.objects.raw(select_query)
            self._ids_to_objects = self._map_out_objects(pre_queried_objects)

    def get_instance(self, instance_loader, row):
        row_id = self._get_id(row)
        match = self._ids_to_objects.get(row_id, None)
        return match

    def _map_out_objects(self, values):
        return {self._get_id(value): value for value in values}

    def _get_id(self, value):
        return '-'.join([str(self._get_header_value(header_id, value)) for header_id in self._meta.import_id_fields])

    def _get_header_value(self, header_id, value):
        header_value = value[header_id] if isinstance(value, dict) else getattr(value, header_id)
        return header_value if header_value else ''

    def _to_where_condition(self, column_name, column_value):
        if column_value:
            return '%s = \'%s\'' % (column_name, column_value)
        else:
            return '%s is null' % column_name

Then I use that BulkQueryMixin in my Resource to fetch all data related to the uploaded import once, and then on every get_instance(), i just retrieve from that cached dict. The code is not pretty, but seems to work and has greatly increased the performance on my end.

But aside from that, I had to do a few more things (ranked in terms of performance gain)

1. Add in my Resource skip_unchanged - removes any update statements which can be one for every row element
2. Modify my django Models to override __deepcopy__ (and __copy__) - this also slows down things substantially
3. Add in my Resource report_skipped - speeds up rendering of the confirmation page. Also, with 10k records uploaded, it makes spotting the difference easier

[franz-see]

@andrewgy8 Good point. I’ll try to see if I can change it to use querysets and filters instead.