Persistent indexes

This is an introduction to ArangoDB’s persistent indexes.

It is possible to define a persistent index on one or more attributes (or paths) of documents. The index is then used in queries to locate documents within a given range. If the index is declared unique, then no two documents are allowed to have the same set of attribute values.

Creating a new document or updating a document will fail if the uniqueness is violated. If the index is declared sparse, a document will be excluded from the index and no uniqueness checks will be performed if any index attribute value is not set or has a value of .

ensures that a unique persistent index exists collection.ensureIndex({ type: "persistent", fields: [ "field1", ..., "fieldn" ], unique: true })

Creates a unique persistent index on all documents using field1, … fieldn as attribute paths. At least one attribute path has to be given. The index will be non-sparse by default.

All documents in the collection must differ in terms of the indexed attributes. Creating a new document or updating an existing document will will fail if the attribute uniqueness is violated.

To create a sparse unique index, set the sparse attribute to true:

collection.ensureIndex({ type: "persistent", fields: [ "field1", ..., "fieldn" ], unique: true, sparse: true })

In a sparse index all documents will be excluded from the index that do not contain at least one of the specified index attributes or that have a value of null in any of the specified index attributes. Such documents will not be indexed, and not be taken into account for uniqueness checks.

In a non-sparse index, these documents will be indexed (for non-present indexed attributes, a value of null will be used) and will be taken into account for uniqueness checks.

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{ 
  "deduplicate" : true, 
  "fields" : [ 
    "myId" 
  ], 
  "id" : "ids/76591", 
  "isNewlyCreated" : true, 
  "name" : "idx_1712165132388270080", 
  "selectivityEstimate" : 1, 
  "sparse" : false, 
  "type" : "persistent", 
  "unique" : true, 
  "code" : 201 
}
{ 
  "_id" : "ids/76595", 
  "_key" : "76595", 
  "_rev" : "_dAzP1O2---" 
}
{ 
  "_id" : "ids/76597", 
  "_key" : "76597", 
  "_rev" : "_dAzP1O6---" 
}
{ 
  "_id" : "ids/76599", 
  "_key" : "76599", 
  "_rev" : "_dAzP1O6--A" 
}
[ArangoError 1210: unique constraint violated - in index idx_1712165132388270080 of type persistent over 'myId'; conflicting key: 76595]

arangosh> db.ids.ensureIndex({ type: "persistent", fields: [ "name.first", "name.last" ], unique: true });
arangosh> db.ids.save({ "name" : { "first" : "hans", "last": "hansen" }});
arangosh> db.ids.save({ "name" : { "first" : "jens", "last": "jensen" }});
arangosh> db.ids.save({ "name" : { "first" : "hans", "last": "hansen" }});

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{ 
  "deduplicate" : true, 
  "fields" : [ 
    "name.first", 
    "name.last" 
  ], 
  "id" : "ids/76572", 
  "isNewlyCreated" : true, 
  "name" : "idx_1712165132380930050", 
  "selectivityEstimate" : 1, 
  "sparse" : false, 
  "type" : "persistent", 
  "unique" : true, 
  "code" : 201 
}
{ 
  "_id" : "ids/76576", 
  "_key" : "76576", 
  "_rev" : "_dAzP1Oa---" 
}
{ 
  "_id" : "ids/76578", 
  "_key" : "76578", 
  "_rev" : "_dAzP1Oe---" 
}
{ 
  "_id" : "ids/76580", 
  "_key" : "76580", 
  "_rev" : "_dAzP1Oe--A" 
}
[ArangoError 1210: unique constraint violated - in index idx_1712165132380930050 of type persistent over 'name.first, name.last'; conflicting key: 76576]

ensures that a non-unique persistent index exists collection.ensureIndex({ type: "persistent", fields: [ "field1", ..., "fieldn" ] })

Creates a non-unique persistent index on all documents using field1, … fieldn as attribute paths. At least one attribute path has to be given. The index will be non-sparse by default.

To create a sparse unique index, set the sparse attribute to true.

In case that the index was successfully created, an object with the index details, including the index-identifier, is returned.

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{ 
  "deduplicate" : true, 
  "fields" : [ 
    "first" 
  "isNewlyCreated" : true, 
  "name" : "idx_1712165132314869760", 
  "selectivityEstimate" : 1, 
  "sparse" : false, 
  "type" : "persistent", 
  "unique" : false, 
  "code" : 201 
}
{ 
  "_id" : "names/76304", 
  "_key" : "76304", 
  "_rev" : "_dAzP1Ke---" 
}
{ 
  "_id" : "names/76306", 
  "_key" : "76306", 
  "_rev" : "_dAzP1Ke--A" 
}
{ 
  "_id" : "names/76308", 
  "_key" : "76308", 
  "_rev" : "_dAzP1Ki---" 
}
{ 
  "_id" : "names/76310", 
  "_key" : "76310", 
  "_rev" : "_dAzP1Ki--A" 
}
{ 
  "_id" : "names/76312", 
  "_key" : "76312", 
  "_rev" : "_dAzP1Km---" 
}

Selects all documents from the collection that match the specified example and returns a cursor. A persistent index will be used if present.

You can use toArray, next, or hasNext to access the result. The result can be limited using the skip and limit operator.

An attribute name of the form a.b is interpreted as attribute path, not as attribute. If you use

{ "a" : { "c" : 1 } }

as example, then you will find all documents, such that the attribute a contains a document of the form {c : 1 }. For example the document

{ "a" : { "c" : 1 }, "b" : 1 }

will match, but the document

will not.

However, if you use

{ "a.c" : 1 },

then you will find all documents, which contain a sub-document in a that has an attribute c of value 1. Both the following documents

and

will match.

To fix persistent indexes after a language change, delete and re-create them.