I am assuming you meant the batch jobs that are/were used in old
world for data cleansing.
As far as I understand there is no hard and fast rule for it and it depends
functional and system requirements of the usecase.
It is also dependent on the technology being used and how it manages
E.g. in HBase or Cassandra, you can write batch jobs which clean or correct
or remove unwanted or incorrect data and than the underlying stores usually have
a concept of compaction which not only defragments data files but also at this
point removes from disk all the entries marked as deleted.
But there are considerations to be aware of given that compaction is a
heavy process and in some cases (e.g. Cassandra) there can be problems when
there are too much data to be removed. Not only that, in some cases,
marked-to-be-deleted data, until it is deleted/compacted can slow down normal
operations of the data store as well.
One can also leverage in HBase's case the versioning mechanism and the
afore-mentioned batch job can simply overwrite the same row key and the previous
version would no longer be the latest. If max-version parameter is configured as
1 then no previous version would be maintained (physically it would be and would
be removed at compaction time but would not be query-able.)
In the end, basically cleansing can be done after or before loading but
given the append-only and no hard-delete design approaches of most nosql stores,
I would say it would be easier to do cleaning before data is loaded in the nosql
store. Of course, it bears repeating that it depends on the use case.
Having said that, on a side-note and a bit off-topic, it reminds me of the
Lamda Architecture that combines batch and real-time computation for big data
using various technologies and it uses the idea of constant periodic refreshes
to reload the data and within this periodic refresh, the expectations are that
any invalid older data would be corrected and overwritten by the new refresh
load. Those basically the 'batch part' of the LA takes care of data cleansing by
reloading everything. But LA is mostly for thouse systems which are ok with
eventually consistent behavior and might not be suitable for some systems.