---
layout: default
description: In ArangoDB there are special indices designed to speed up graph operations,especially if the graph contains supernodes (vertices that have an exceptionallyhigh amount of connected edges)
---
Vertex Centric Indexes
======================

Introduction to Vertex Centric Indexes
--------------------------------------

In ArangoDB there are special indices designed to speed up graph operations,
especially if the graph contains supernodes (vertices that have an exceptionally
high amount of connected edges).
These indices are called vertex centric indexes and can be used in addition
to the existing edge index.

Motivation
----------

The idea of this index is to index a combination of a vertex, the direction and any arbitrary
set of other attributes on the edges.
To take an example, if we have an attribute called `type` on the edges, we can use an outbound
vertex-centric index on this attribute to find all edges attached to a vertex with a given `type`.
The following query example could benefit from such an index:

    FOR v, e, p IN 3..5 OUTBOUND @start GRAPH @graphName
      FILTER p.edges[*].type ALL == "friend"
      RETURN v

Using the built-in edge-index ArangoDB can find the list of all edges attached to the vertex fast,
but still it has to walk through this list and check if all of them have the attribute `type == "friend"`.
Using a vertex-centric index would allow ArangoDB to find all edges for the vertex having the attribute `type == "friend"`
in the same time and can save the iteration to verify the condition.

Index creation
--------------

A vertex-centric can be either of the following types:

* [Hash Index](indexing-hash.html)
* [Skiplist Index](indexing-skiplist.html)
* [Persistent Index](indexing-persistent.html)

And is created using their creation operations.
However in the list of fields used to create the index we have to include either `_from` or `_to`.
Let us again explain this by an example.
Assume we want to create an hash-based outbound vertex-centric index on the attribute `type`.
This can be created with the following way:
{% arangoshexample examplevar="examplevar" script="script" result="result" %}
    @startDocuBlockInline ensureVertexCentricHashIndex
    @EXAMPLE_ARANGOSH_OUTPUT{ensureVertexCentricHashIndex}
    ~db._createEdgeCollection("collection");
    db.collection.ensureIndex({ type: "hash", fields: [ "_from", "type" ] })
    ~db._drop("collection");
    @END_EXAMPLE_ARANGOSH_OUTPUT
    @endDocuBlock ensureVertexCentricHashIndex
{% endarangoshexample %}
{% include arangoshexample.html id=examplevar script=script result=result %}
All options that are supported by the respective indexes are supported by the vertex-centric index as well.

Index usage
-----------

The AQL optimizer can decide to use a vertex-centric whenever suitable, however it is not guaranteed that this
index is used, the optimizer may estimate that an other index is assumed to be better.
The optimizer will consider this type of indexes on explicit filtering of `_from` respectively `_to`:

    FOR edge IN collection
      FILTER edge._from == "vertices/123456" AND edge.type == "friend"
      RETURN edge

and during pattern matching queries:

    FOR v, e, p IN 3..5 OUTBOUND @start GRAPH @graphName
      FILTER p.edges[*].type ALL == "friend"
      RETURN v