We plan to change a legacy Firestore in Datastore mode database from OPTIMISTIC_WITH_ENTITY_GROUPS to PESSIMISTIC:
gcloud firestore databases update --database='(default)' --concurrency-mode=PESSIMISTIC
Its createTime value is 1970-01-01T00:00:00Z since it was originally created before 2016 and upgraded from Cloud Datastore. We do not use the Remote API, and our application already runs against PESSIMISTIC in a non-production environment. We saw that there is an unresolved public report of this operation returning 500 INTERNAL on a legacy (App Engine v1 origin) database: Cannot change concurrency mode… (500 response).
Is changing a legacy (pre-2016 / OPTIMISTIC_WITH_ENTITY_GROUPS) database’s concurrency mode to PESSIMISTIC fully supported? Is that 500 a known issue for databases created originally with App Engine v1, and is there any prerequisite or step we should take first?