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Neo4j Internals: Transactions, Availability, Scale

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Part of the Neo4j internals series: Native Graph Processing | Native Graph Storage | Transactions, Availability, Scale

Transactions ​

Neo4j supports full ACID transactions:

  • Every modification runs inside a transaction.

  • Write-ahead log ensures durability: Changes are logged before being applied to store files.

  • Transactions can span multiple nodes, relationships, and properties.

Recoverability ​

  • Write-ahead log for crash recovery.

  • On restart, Neo4j replays uncommitted transactions from the log.

Availability ​

  • Master-slave replication with automatic failover.

  • Slaves serve reads immediately. Writes go to master and propagate.

  • On master failure, a slave is elected as new master.

Scale ​

  • Reads: Scale horizontally by adding slaves.

  • Writes: Scale vertically (single master).

  • Cache sharding: Route requests to instances with relevant portions of the graph in memory.

  • Graph sharding (splitting the graph across machines): Remains an open research problem. Cutting a graph inevitably severs relationships, degrading traversal performance.