Database Reference
In-Depth Information
the expected number of nodes, relationships, properties, number of users, and so on. This
calculator deals not only with disk storage capacity, but also RAM and clustering setup re-
commendations.
Itshouldbestressedthatthiscalculatorisonlymeanttoprovidearoughestimate.Ifyou're
embarkingonamission-critical project,you'readvisedtoseekamoreaccurateassessment
from qualified engineers, which can take many other factors into consideration. But for a
rough and ready starting calculation, this calculator will generally serve just fine.
You can find the hardware sizing calculator on the Neo Technology site,
www.neotechnology.com/hardware-sizing .
11.1.3. Store files
Neo4jstoresvariouspartsofthegraphstructureinasetoffilesknownas store files .These
storefilesaregenerallybrokendownbyrecordtype—thereareseparatefilesfornodes,re-
lationships, properties, labels, and so on. The structure and layout of the data in these files
has specifically been designed and optimized to provide an efficient storage format that
the Neo4j runtime engine can exploit to provide very performant lookups and traversals
through the graph. One of the core enablers is the fact that Neo4j stores data according to
the index-free adjacency principle.
The index-free adjacency what?
The index-free adjacency principle (or property) is a fancy term that refers to graph data-
basesthatareabletostoretheirdatainaveryparticularway.Specifically,eachnodestored
within the database must have a direct link or reference to its adjacent nodes (those nodes
directly connected to it) and must not need to make use of any additional helper structures
(such as an index) to find them.
By storing its data in this manner, Neo4j is able to follow pointers directly to connected
nodes and relationships when performing traversals, making this type of access extremely
fast compared to non-index-free adjacency stores, such as the traditional relational data-
base. In Neo4j there's no overhead incurred when trying to locate immediately connected
nodes; non-index-free adjacency stores would first need to use a supporting (index) struc-
 
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