Chapter 3. Transaction management

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In order to fully maintain data integrity and ensure good transactional behavior, Neo4j supports the ACID properties:

atomicity - if any part of a transaction fails, the database state is left unchanged
consistency - any transaction will leave the database in a consistent state
isolation - during a transaction, modified data cannot be accessed by other operations
durability - the DBMS can always recover the results of a committed transaction

Specifically:

All modifications to Neo4j data must be wrapped in transactions.
The default isolation level is READ_COMMITTED.
Data retrieved by traversals is not protected from modification by other transactions.
Non-repeatable reads may occur (i.e., only write locks are acquired and held until the end of the transaction).
One can manually acquire write locks on nodes and relationships to achieve higher level of isolation (SERIALIZABLE).
Locks are acquired at the Node and Relationship level.
Deadlock detection is built into the core transaction management.