While monitoring your Neo4j environment, you may wonder why you see higher planning times after creating indexes or constraints.

Creating and dropping indexes are considered schema changes. The same applies to the creation and deletion of constraints. As an effect of a schema change in Neo4j, the schema cache will be cleared and as a result the planner cache is cleared as well.  The intent here is to ensure that all plans can leverage new indexes/constraints and avoid the usage of dropped indexes/constraints. This is the by design of Neo4j.

This also indicates that the use of replan=skip cannot be utilized and will be ignored as the planner will still need to replan the query as a consequence of the plan no longer being in the cache. Queries may take slightly longer until the cache becomes populated.

Additional References:

Knowledge Article:  Understanding the Query Plan Cache
Neo4j Documentation: Query Caches