The technique that the developer should implement to ensure the query performs optimally, while preserving the entire result set, is to break down the query into two individual queries and join the two result sets. This is because the query in the code snippet is using a complex filter condition that combines the CreatedDate and RecordType fields, which are not indexed by default. This means that the query will perform a full table scan on the Account object, which can be very slow and inefficient when the data volume is large. To avoid this, the developer can split the query into two queries, one that filters by the CreatedDate field and another that filters by the RecordType field. Then, the developer can use a Set or a Map to store the Ids of the Accounts that match both criteria, and use the Set or the Map to retrieve the Account records from the database. This way, the query will use the standard indexes on the Id, CreatedDate, and RecordType fields, and perform faster and more efficiently.