Here are some Delta migration General understanding
Data Migration Tool migrates data created only by Magento's own modules (eg.
Orders, Customers Profile) and is not responsible for the code or extensions made by third-party developers.
If these extensions created data in the frontend database and the merchant wants to have this data in Magento 2, then config files of the Data Migration Tool should be created and modified accordingly.
After main Data Migration, Data added to the Magento 1 database (eg. Data added by customer on frontend). To migrate these data in Magento 2, This Delta tool will Database triggers for tables.
Changes may include revisions to your Product Categories, Products themselves --again, the Deltas do track changes in inventory, so excluding that. Not recommend to deleting products that were migrated, as the delta may blow up when attempting to update the inventory for deleted product(s) -- CMS Pages, Static Blocks.
The deltas, do not track every change on the M1 database. For example you can go ahead and make all the changes you like to store configuration, as there is no Deltas for that.
So, While we do incremental Migrations, its enables you to migrate only the changes made in Magento 1 since the last time you migrated data. These changes are:
Data that customers added via storefront (created orders, reviews,
changes in customer profiles, etc.)
All operations with orders in the
Magento Admin panel
- Catalog Inventory Stock changes.
Not recommend doing any of the following on your M2 database after your initial migration if you plan to run Deltas with it's default configuration:
- Add/Remove products (on either DB. If you do add the product to both databases at the same time in the same order so that their entity_id on both databases match, this is only for inventory reasons, not attribute information reasons)
- Add/Remove customers
- Create any new orders
- Attempt to manage product inventory