How to troubleshoot a missing index or constraint ?

If you created some constraint ( CREATE CONSTRAINT) or index ( CREATE INDEX on nodes or relationship or a fulltext index via db.index.fulltext.createNodeIndex or db.index.fulltext.createRelationshipIndex) and subsequently receive an error stating the index or constraint is missing when making a Cypher query or any API call that would rely on that same index / constraint please check the following:

• Check the index or constraint was successfully created with CALL db.index()   
• Review the log file query.log for any index or constraint drop (drop index, drop constraint)
• Review your queries and check any calls to CALL apoc.schema.assert(...).
  The default behaviour is that when calling
  apoc.schema.assert({indexLabel:[indexKeys],…​},{constraintLabel:[constraintKeys],…​}, dropExisting : true) yield label, key, unique, action
  the last parameter dropExisting is by default true and therefore the schema is replaced.
  See http://neo4j-contrib.github.io/neo4j-apoc-procedures/3.5/indexes/schema-index-operations/
• Check that no database dump or database export has been loaded that would overwrite the existing "schema". This can be found in the `neo4j.log` file.
• Finally, if all the above fail, try to regularly poll on CALL db.index() and log the output to a debug file in order to narrow down the time interval of the issue and review the queries or events.

For further help, please reach out to the technical support.