Using incremental materialisation of cost_per_query model over-allocates cost per query

[bisset-a]

Hey there!

We noticed the cost_per_query model seems to over-allocate cost to some queries.

I think the issue comes from the incremental logic in this line. This line returns a timestamp. Later in the model, cost is attributed based on the hour the query falls into. When the timestamp generated in L34 is close to the hour (e.g. 03:57). In this case, all warehouse cost for the hour between 3:00 and 4:00 will be allocated to the queries that ended between 03:57 and 4:00 (which causes an over-allocation as there won't be many queries that occur in this space of 3mins).

Aggregated query cost per day using the incremental materialization we have been running for ~4 months gives quite different results from a table materialization.

Let me know if you would like me to investigate further and raise a PR. Thanks so much!!