AccumuloGraph/table-structure.md

AccumuloGraph Table Schema

AccumuloGraph uses a number of backing tables for data storage. This file documents the structure and organization of these tables. The tables and records are structured in such a way as to implement the Blueprints operations in terms of efficient Accumulo operations, i.e., prefix searches, contiguous scans, and batch operations. For our purposes, Accumulo entries consist of four fields: row (R), column family (CF), column qualifier (CQ), and value (V). For more information on Accumulo's schema and how to access records efficiently, see the Accumulo documentation.

The tables used by AccumuloGraph are prefixed by the configured graph name and can be classed as element/property tables, and index tables. Their structure is discussed below.

Elements and properties

Vertex and edge information, along with their properties, are stored in the graphname_vertex and graphname_edge tables respectively.

First, an entry declares the existence of a vertex in the vertex table.

R	CF	CQ	V
vertex_id	_LABEL_	_EXISTS_	[empty]

A similar entry declares the existence of an edge in the edge table.

R	CF	CQ	V
edge_id	_LABEL_	in_vertex_id_DELIM_out_vertex_id	edge_label

When adding an edge, additional entries are stored in the vertex table for each endpoint of the edge. These facilitate the Vertex.getEdge and Vertex.getVertex operations.

R	CF	CQ	V
in_vertex_id	_IN_EDGE_	out_vertex_id_DELIM_edge_id	edge_label
out_vertex_id	_OUT_EDGE_	in_vertex_id_DELIM_edge_id	edge_label

Finally, vertex and edge properties are stored in their respective tables. Entry formats are the same for both vertices and edges. Note that property values are serialized such that their type can be deduced when deserializing.

R	CF	CQ	V
element_id	property_key	[empty]	property_value

Indexes

Several tables store index-related information, including index value tables that store index property keys and values, and index metadata tables that store information about what indexes exist and what properties are indexed.

For KeyIndexableGraph, index value tables include graphname_vertex_key_index and graphname_edge_key_index for vertex and edge properties, respectively. For IndexableGraph, index value tables are named graphname_index_indexname, where indexname is the index name. The entry formats in all these tables are the same:

R	CF	CQ	V
property_value	property_key	element_id	[empty]

Property values are serialized in the same way as above.

Two index metadata tables store index information. For KeyIndexableGraph, graphname_indexed_keys enumerates the property keys that are indexed in graphname_vertex_key_index and graphname_edge_key_index.

R	CF	CQ	V
property_key	element_class	[empty]	[empty]

For IndexableGraph, graphname_index_names lists the existing indexes.

R	CF	CQ	V
index_name	element_class	[empty]	[empty]