Syncmaven supports incremental syncs. This means that subsequent syncs will only fetch the data that has changed since the last sync. Plus, it supports checkpointing via same mechanism. If long-running sync fails in the middle, the next run will carry on from where it left off.

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Cursors

The main mechanism for incremental syncs is cursors. A cursor is a field in model that only grows over time. For example, updated_at field in a table is a good candidate for cursor, or id if it is auto-incrementing. Cursors are defined in model 
--{{ config "name" "Users" }}
--{{ config "datasource" env.DATABASE_URL }}
--{{ config "cursor" "updated_at" }}

select * from users where :cursor is null or updated_at >= :cursor
In the model configuration above, cursor is defined as updated_at. The model will only fetch rows where update_at value is greater than the last cursor value, which is stored in the sync state and referenced by :cursor in the query.
For the first runs, and full refreshes, the cursor value will be null. It means that all rows will be fetched. So the query should be able to handle null cursor value properly, note the :cursor is null part in the query.

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Checkpointing

The same mechanism is used for checkpointing. Sync will save a cursor value periodically, after a batch of 100 rows by default. If the sync fails in the middle, the next run will start from the last saved cursor value.