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Version: 2.5.0

Data durability and backup

Memgraph uses two mechanisms to ensure the durability of stored data and make disaster recovery possible:

  • write-ahead logging (WAL)
  • periodic snapshot creation

These mechanisms generate durability files and save them in the respective wal and snapshots folders in the data directory. Data directory stores permanent data on-disk.

The default data directory path is var/lib/memgraph but the path can be changed by modifying the data-dir configuration flag.

To encrypt the data directory, use LUKS as it works with Memgraph out of the box and is undetectable from the applications perspective so it shouldn't break any existing applications.

Related - How-to

Durability mechanisms​

To configure the durability mechanisms check their respective configuration flags in the configuration reference guide.

If you need help configuring Memgraph, check out the configuration how-to guide.

Write-ahead logging​

Write-ahead logging (WAL) is a technique applied in providing atomicity and durability to database systems. Each database modification is recorded in a log file before being written to the DB and therefore the log file contains all steps needed to reconstruct the DB’s most recent state.

Memgraph has WAL enabled by default. To switch it on and off, use the boolean storage-wal-enabled flag. For other WAL-related flags check the configuration reference guide.

WAL files are usually located at /var/lib/memgraph/wal.

Snapshots​

Snapshots provide a faster way to restore the states of your database. Memgraph periodically takes snapshots during runtime and upon exit. When a snapshot is triggered, the entire data storage is written to the drive. On startup, the database state is recovered from the most recent snapshot file. The timestamp of the snapshot is compared with the latest update recorded in the WAL file and, if the snapshot is less recent, the state of the DB will be recovered using the WAL file.

Memgraph has snapshot creation enabled by default. You can configure the exact snapshot creation behavior by defining the relevant flags. Alternatively, you can make one directly by running the following query:

CREATE SNAPSHOT;

Snapshot files are saved inside the snapshots directory located in the data directory (var/lib/memgraph).

caution

Snapshots and WAL files are presently not compatible between Memgraph versions.

Backup and restore​

You can easily back up Memgraph by following a four-step process:

  1. Lock the data directory with the LOCK DATA DIRECTORY; query.
  2. Create a snapshot with the CREATE SNAPSHOT; query.
  3. Copy the snapshot from the snapshots directory to a backup location.
  4. Unlock the directory with the UNLOCK DATA DIRECTORY; query.

Locking the data directory ensures that no files are deleted by the system.

To restore from back-up:

  1. Start an instance by adding a -v ~/snapshots:/var/lib/memgraph/snapshots flag to the docker run command, where the ~/snapshots represents a path to the local directory with the back-up snapshot, for example: 

    docker run -p 7687:7687 -p 7444:7444 -v ~/snapshots:/var/lib/memgraph/snapshots memgraph/memgraph

Check out a detailed guide.

Database dump​

The database dump contains a record of the database state in the form of Cypher queries. It’s equivalent to the SQL dump in relational DBs.

You can run the queries constituting the dump to recreate the state of the DB as it was at the time of the dump.

To dump the Memgraph DB, run the following query:

DUMP DATABASE;

If you are using Memgraph Lab, you can dump the database, that is, the queries to recreate it, to a CYPHERL file in the Import & Export section of the Lab.