Skiplists

It is possible to define a skiplist index on one or more attributes (or paths)of documents. This skiplist is then used in queries to locate documentswithin a given range. If the skiplist is declared unique, then no two documents areallowed 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 skiplist index is declared sparse, a document will be excluded from the index and nouniqueness checks will be performed if any index attribute value is not set or has a valueof .

Accessing Skiplist Indexes from the Shell

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

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

All documents in the collection must differ in terms of the indexedattributes. Creating a new document or updating an existing document willfail if the attribute uniqueness is violated.

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

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

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

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

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

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{ 
  "deduplicate" : true, 
  "fields" : [ 
    "myId" 
  ], 
  "id" : "ids/16443", 
  "isNewlyCreated" : true, 
  "sparse" : false, 
  "type" : "skiplist", 
  "unique" : true, 
  "code" : 201 
}
{ 
  "_id" : "ids/16446", 
  "_key" : "16446", 
  "_rev" : "_ZHpYtFm--_" 
}
{ 
  "_id" : "ids/16450", 
  "_key" : "16450", 
  "_rev" : "_ZHpYtFm--B" 
}
{ 
  "_id" : "ids/16453", 
  "_key" : "16453", 
  "_rev" : "_ZHpYtFm--D" 
}
[ArangoError 1210: unique constraint violated - in index 16443 of type skiplist over ["myId"]; conflicting key: 16446]

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arangosh> db.ids.ensureIndex({ type: "skiplist", 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": "jensen" }});
arangosh> db.ids.save({ "name" : { "first" : "hans", "last": "hansen" }});

{ 
  "deduplicate" : true, 
  "fields" : [ 
    "name.first", 
    "name.last" 
  ], 
  "id" : "ids/16424", 
  "sparse" : false, 
  "type" : "skiplist", 
  "unique" : true, 
  "code" : 201 
}
{ 
  "_id" : "ids/16427", 
  "_key" : "16427", 
  "_rev" : "_ZHpYtCi--_" 
}
{ 
  "_id" : "ids/16431", 
  "_key" : "16431", 
  "_rev" : "_ZHpYtCm--_" 
}
{ 
  "_id" : "ids/16434", 
  "_key" : "16434", 
  "_rev" : "_ZHpYtCm--B" 
}
[ArangoError 1210: unique constraint violated - in index 16424 of type skiplist over ["name.first","name.last"]; conflicting key: 16427]

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Ensures that a non-unique skiplist index exists:

Creates a non-unique skiplist 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 non-unique index, set the sparse attribute to true.

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

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

Show execution results

{ 
  "deduplicate" : true, 
  "fields" : [ 
    "first" 
  ], 
  "id" : "names/16290", 
  "isNewlyCreated" : true, 
  "sparse" : false, 
  "type" : "skiplist", 
  "unique" : false, 
  "code" : 201 
}
{ 
  "_id" : "names/16293", 
  "_key" : "16293", 
  "_rev" : "_ZHpYst2--_" 
}
{ 
  "_id" : "names/16297", 
  "_key" : "16297", 
  "_rev" : "_ZHpYst2--B" 
}
{ 
  "_id" : "names/16300", 
  "_key" : "16300", 
}
{ 
  "_id" : "names/16303", 
  "_key" : "16303", 
  "_rev" : "_ZHpYst6--B" 
}
{ 
  "_id" : "names/16306", 
  "_key" : "16306", 
  "_rev" : "_ZHpYsu---_" 
}

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Ensures that a skiplist array index exists (non-unique):collection.ensureIndex({ type: "skiplist", fields: [ "field1[]", …, "fieldn[]" ] })

Creates a non-unique skiplist array index for the individual elements of the arrayattributes field1[], … fieldn[ found in the documents. At leastone attribute path has to be given. The index always treats the indexed arrays assparse.

It is possible to combine array indexing with standard indexing:collection.ensureIndex({ type: "skiplist", fields: [ "field1[*]", "field2" ] })

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

arangosh> db.test.ensureIndex({ type: "skiplist", fields: [ "a[*]" ] });
arangosh> db.test.save({ a : [ 1, 2 ] });
arangosh> db.test.save({ a : [ 1, 3 ] });
arangosh> db.test.save({ a : null });

{ 
  "deduplicate" : true, 
  "fields" : [ 
    "a[*]" 
  ], 
  "id" : "test/16313", 
  "isNewlyCreated" : true, 
  "sparse" : false, 
  "type" : "skiplist", 
  "unique" : false, 
  "code" : 201 
}
{ 
  "_id" : "test/16316", 
  "_key" : "16316", 
  "_rev" : "_ZHpYsw2--_" 
}
{ 
  "_id" : "test/16320", 
  "_key" : "16320", 
  "_rev" : "_ZHpYsw6--_" 
}
{ 
  "_id" : "test/16323", 
  "_key" : "16323", 
  "_rev" : "_ZHpYsw6--B" 
}

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Constructs a query-by-example using a skiplist index:collection.byExample(example)

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

You can use toArray, next, or hasNext to access theresult. 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

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

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

will match, but the document

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

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.