If you look closely, Neo4j Desktop is showing a small warning sign next to the query text editor. If you click on this warning, it will show an explanation about it. In our case, it says this:
The execution plan for this query contains the Eager operator, which forces all dependent data to be materialized in main memory before proceeding
This is not directly related to a data import, but this is often the first time we face this warning message, so let's try to understand it.
The Neo4j documentation defines the Eager operator in this sentence:
For isolation purposes, the operator ensures that operations affecting subsequent operations are executed fully for the whole dataset before continuing execution.
In other words, each statement of the query is executed for each row of the file, before moving to the other row. This is usually not a problem because a Cypher statement will deal with a hundred nodes or so, but when importing large data files, the overhead...
