Architecture

AppendOnly/MVCC

Instead of overwriting existing documents, ArangoDB will create a new version of modified documents. This is even the case when a document gets deleted. Thetwo benefits are:

• Objects can be stored coherently and compactly in the main memory.
• Objects are preserved, isolated writing and reading transactions allowaccessing these objects for parallel operations.The system collects obsolete versions as garbage, recognizing them asforsaken. Garbage collection is asynchronous and runs parallel to otherprocesses.

Mostly Memory/Durability

Database documents are stored in memory-mapped files. Per default, thesememory-mapped files are synced regularly but not instantly. This is often a goodtradeoff between storage performance and durability. If this level of durabilityis too low for an application, the server can also sync all modifications todisk instantly. This will give full durability but will come with a performancepenalty as each data modification will trigger a sync I/O operation.