Below are the limitations of the OrientDB engine:
- Databases: There is no limit to the number of databases per server or embedded. Users reported no problem with 1000 databases open
- Clusters: each database can have a maximum of 32,767 clusters (2^15-1)
- Records per cluster (Documents, Vertices and Edges are stored as records): can be up to 9,223,372,036,854,780,000 (2^63-1), namely 9,223,372 Trillion records
- Records per database (Documents, Vertices and Edges are stored as records): can be up to 302,231,454,903,000,000,000,000 (2^78-1), namely 302,231,454,903 Trillion records
- Record size: up to 2GB each, even if we suggest avoiding the creation of records larger than 10MB. They can be split into smaller records, take a look at Binary Data
- Document Properties can be:
- up to 2 Billion per database for schema-full properties
- there is no limitation regarding the number of properties in schema-less mode. The only concrete limit is the size of the Document where they can be stored. Users have reported no problems working with documents made of 15,000 properties
- Indexes can be up to 2 Billion per database. There are no limitations regarding the number of indexes per class
- Queries can return a maximum of 2 Billion rows, no matter the number of the properties per record
- Concurrency level: in order to guarantee atomicity and consistency, OrientDB acquire an exclusive lock on the storage during transaction commit. This means transactions are serialized. Giving this limitation, the OrientDB team is already working on improving parallelism to achieve better scalability on multi-core machines by optimizing internal structure to avoid exclusive locking.
Look also at the limitations with distributed setup.