Transactions are an integral part of the Neo4j ecosystem and primarily dominated by the use of two major components—the Write-Ahead Log (WAL) and the Wait-For Graph (WFG) for detection of deadlocks prior to their occurrence.
The WAL in the Neo4j transaction system ensures atomicity and durability in transactions. Every change during a transaction persists on disk as and when the request for the change is received, without modifying the database content. When the transaction is committed, the changes are made to the data store and subsequently removed from the disk. So, when the system fails during a commit, the transactions can be read back and database changes can be ensured. This guarantees atomic changes and durability of commit operations.
All the changes during transactions occur in states. On initiating a transaction (with the beginTx() method), a state called TX_STARTED is assigned to it. There are similar states assigned while preparing a transaction...