Working with Indexes
Create and manage indexes programmatically for document collections using ArangoDB’s JavaScript API
Index Identifiers
An index identifier uniquely identifies an index within a collection.
It is a numeric value stored as a string that is auto-generated by ArangoDB.
It can be prefixed with a collection name and forward slash (/
) to uniquely
identify an index within a database.
A specific index of a collection can be accessed using its index identifier as follows:
db.collection.index("<index-identifier>");
db.collection.index("<collection-name>/<index-identifier>");
db._index("<collection-name>/<index-identifier>");
For example, assume that the full index identifier, which is stored in the _id
attribute of the index, is demo/362549736
, and the index has been created in a
collection named demo
. Then this index can be accessed as follows:
db.demo.index("362549736");
db.demo.index("demo/362549736");
Because the full index identifier is unique within the database, you can also
access the index directly from the db
object:
db._index("demo/362549736");
You can also look up an index by its name. Since names are only unique within
a collection rather than within the database, the lookup must also include the
collection name when calling db._index()
:
db.demo.index("primary")
db._index("demo/primary")
Collection Methods
Listing all indexes of a collection
collection.getIndexes(withStats, withHidden)
collection.indexes(withStats, withHidden)
Returns an array of all indexes defined for the collection.
You can set the following parameters:
withStats
(boolean, optional): whether to include index figures and estimates in the result. Default:false
withHidden
(boolean, optional): whether to include hidden indexes in the result. Internal indexes (such asarangosearch
) and ones that are currently built in the background are hidden. Default:false
The indexes()
method is an alias for getIndexes()
.
Note that _key
implicitly has an index assigned to it.
Examples
Get the index definitions for a collection:
db.test.getIndexes();
Get the index definitions for a collection, including figures and hidden indexes:
db.coll.indexes(true, true);
Creating an index
Ensures that an index exists:
collection.ensureIndex(index-description)
Ensures that an index according to the index-description
exists. A
new index will be created if none exists with the given description.
Calling this method returns an index object. Whether or not the index
object existed before the call is indicated in the isNewlyCreated
return
attribute.
The index-description
input value must contain at least a type
attribute.
Other attributes may be necessary, depending on the index type.
type
: can be one of the following values:"persistent"
: persistent (array) index, including vertex-centric index"inverted"
: inverted index"ttl"
: time-to-live index"fulltext"
: full-text index (deprecated from ArangoDB 3.10 onwards)"geo"
: geo-spatial index, with one or two attributes"zkd"
: multi-dimensional index (experimental)
fields
: an array of attribute paths, containing the document attributes (or sub-attributes) to be indexed. Some indexes allow using only a single path, and others allow multiple. If multiple attributes are used, their order matters.The
.
character denotes sub-attributes in attribute paths. Attributes with literal.
in their name cannot be indexed. Attributes with the name_id
cannot be indexed either, neither as a top-level attribute nor as a sub-attribute (except the inverted index type).If an attribute path contains an
[*]
extension (e.g.friends[*].id
), it means that the index attribute value is treated as an array and all array members are indexed separately. This is possible withpersistent
andinverted
indexes.storedValues
: in indexes of typepersistent
andinverted
, additional attributes can be stored in the index. These additional attributes cannot be used for index lookups or for sorting, but they can be used for projections. This allows an index to fully cover more queries and avoid extra document lookups. Non-existing attributes are stored asnull
values insidestoredValues
. The maximum number of attributes instoredValues
is 32. It is not possible to create multiple indexes with the samefields
attributes and uniqueness but differentstoredValues
attributes. That means the value ofstoredValues
is not considered in index creation calls when checking if an index is already present or needs to be created. In unique indexes, only the attributes infields
are checked for uniqueness, but the attributes instoredValues
are not checked for their uniqueness.In
persistent
indexes, you cannot store attributes with the name_id
, neither as a top-level attribute nor as a sub-attribute.name
: can be a string. Index names are subject to the same character restrictions as collection names. If omitted, a name will be auto-generated so that it is unique with respect to the collection, e.g.idx_832910498
.The purpose of user-defined index names is have easy-to-remember names to use in index hints in AQL queries. If no index hints are used, going with the auto-generated index names is fine.
sparse
: can betrue
orfalse
. You can control the sparsity forpersistent
indexes. Theinverted
,fulltext
, andgeo
index types are sparse by definition.unique
: can betrue
orfalse
and is supported bypersistent
indexes. By default, all user-defined indexes are non-unique. Only the attributes infields
are checked for uniqueness. Any attributes in fromstoredValues
are not checked for their uniqueness.deduplicate
: can betrue
orfalse
and is supported by array indexes of typepersistent
. It controls whether inserting duplicate index values from the same document into a unique array index will lead to a unique constraint error or not. The default value istrue
, so only a single instance of each non-unique index value will be inserted into the index per document. Trying to insert a value into the index that already exists in the index will always fail, regardless of the value of this attribute.estimates
: can betrue
orfalse
and is supported by indexes of typepersistent
. This attribute controls whether index selectivity estimates are maintained for the index. Not maintaining index selectivity estimates can have a slightly positive impact on write performance. The downside of turning off index selectivity estimates will be that the query optimizer will not be able to determine the usefulness of different competing indexes in AQL queries when there are multiple candidate indexes to choose from. Theestimates
attribute is optional and defaults totrue
if not set. It will have no effect on indexes other thanpersistent
(withhash
andskiplist
being mere aliases for thepersistent
index type nowadays).cacheEnabled
: can betrue
orfalse
and is supported by indexes of typepersistent
. The attribute controls whether an extra in-memory hash cache is created for the index. The hash cache can be used to speed up index lookups. The cache can only be used for queries that look up all index attributes via an equality lookup (==
). The hash cache cannot be used for range scans, partial lookups or sorting. The cache will be populated lazily upon reading data from the index. Writing data into the collection or updating existing data will invalidate entries in the cache. The cache may have a negative effect on performance in case index values are updated more often than they are read. The maximum size of cache entries that can be stored is currently 4 MB, i.e. the cumulated size of all index entries for any index lookup value must be less than 4 MB. This limitation is there to avoid storing the index entries of “super nodes” in the cache.cacheEnabled
defaults tofalse
and should only be used for indexes that are known to benefit from an extra layer of caching.
Also check the documentation of the specific index type for additional options.
Examples
db.test.ensureIndex({ type: "persistent", fields: [ "a" ], sparse: true });
db.test.ensureIndex({ type: "persistent", fields: [ "a", "b" ], unique: true });
Dropping an index via a collection object
collection.dropIndex(index)
Delete the specified index using an index object.
If the index does not exist or cannot be dropped, then an error is raised.
If the index existed and has been dropped, then true
is returned.
Note that you cannot drop certain indexes (e.g. the primary index of a collection or the edge index of an edge collection).
collection.dropIndex(index-identifier)
Delete the specified index using an index identifier.
var idx1 = db.example.ensureIndex({ type: "persistent", fields: ["a", "b"] });
var idx2 = db.example.ensureIndex({ type: "persistent", fields: ["c"] });
var indexInfo = db.example.getIndexes();
indexInfo;
db.example.dropIndex(indexInfo[1])
db.example.dropIndex(indexInfo[2].id)
indexInfo = db.example.getIndexes();
Load Indexes into Memory
Loads suitable indexes of this collection into memory:
collection.loadIndexesIntoMemory()
This function tries to cache index entries of this collection in main memory. Index lookups that can be served from the memory cache can be much faster than lookups not stored in the cache, so you can get a nice performance boost.
The function iterates over suitable indexes of the collection and stores the indexed values, not the entire document data, in memory. This is implemented for edge indexes only.
The function returns as soon as the index warmup has been scheduled. The index warmup may still be ongoing in the background, even after the function has already returned. As all suitable indexes are scanned, it may cause significant I/O activity and background load.
This function honors memory limits. If the indexes you want to load are smaller than your memory limit, this function guarantees that most index values are cached. If the index is larger than your memory limit, this function fills up values up to this limit and there is no way to control which indexes of the collection should have priority over others.
It is guaranteed at all times that the in-memory cache data is consistent with the stored index data.
db.example.loadIndexesIntoMemory();
Database Methods
Fetching an index by identifier
db._index(index-identifier)
Find and return the specified index, or null
if no such index exists.
db.example.ensureIndex({ type: "persistent", fields: [ "a", "b" ] });
var indexInfo = db.example.getIndexes().map(function(x) { return x.id; });
indexInfo;
db._index(indexInfo[0])
db._index(indexInfo[1])
Dropping an index via a database object
db._dropIndex(index)
Delete the specified index using an index object.
If the index does not exist or cannot be dropped, an error is raised.
If the index existed and has been dropped, then true
is returned.
db._dropIndex(index-identifier)
Drop the specified index using an index identifier.
var idx1 = db.example.ensureIndex({ type: "persistent", fields: [ "a", "b" ] });
var idx2 = db.example.ensureIndex({ type: "persistent", fields: [ "c" ] });
var indexInfo = db.example.getIndexes();
indexInfo;
db._dropIndex(indexInfo[1])
db._dropIndex(indexInfo[2].id)
indexInfo = db.example.getIndexes();
Revalidating whether an index is used
So you’ve created an index, and since its maintenance isn’t for free, you definitely want to know whether your query can utilize it.
You can use explain to verify that a certain index is used:
var explain = require("@arangodb/aql/explainer").explain;
var idx = db.example.ensureIndex({ type: "persistent", fields: [ "a", "b" ] });
explain("FOR doc IN example FILTER doc.a < 23 RETURN doc", {colors: false});
You can omit colors: false
to get syntax highlighting in arangosh.