# Documents

Vespa models data as documents. A document has a string identifier, set by the application, unique across all documents. A document is a set of key-value pairs. A document has a schema (i.e. type), defined in the search definition.

When configuring clusters, a documents element set what document types a cluster is to store. This configuration is used to configure the garbage collector if it is enabled. Additionally it is used to define default routes for documents sent into the application. By default, a document will be sent to all clusters having the document type defined. Refer to routing for details.

Vespa uses the document ID to distribute documents to nodes. From the document identifier, the content layer calculates a numeric location. A bucket contains all the documents, where a given amount of least significant bits of the location are all equal. This property is used to enable co-localized storage of documents - read more in buckets and elastic Vespa.

Documents can be global, see parent/child.

## Document IDs

The document identifiers are URIs, represented by a string, which must conform to a defined URI scheme for document identifiers. The document identifier string may only contain text characters, as defined by isTextCharacter in com.yahoo.text.Text Schemes have two parts:

Namespace Intended to be used to distinguish data from users who share the same Vespa cluster and/or distinguish between different document types in search. It is hence possible for various applications to use the same Vespa installation, ensuring they do not create document identifier collisions. Application specific.

### id scheme

Vespa has defined one scheme, the id scheme. Format: id:<namespace>:<document-type>:<key/value-pairs>:<user-specified>

namespaceRequiredSee above
document-typeRequiredDocument type as defined in services.xml and the search definition
key/value-pairsOptional

Modifiers to the id scheme, used to configure document distribution. With no modifiers, the id scheme distributes all documents uniformly. The <key/value-pairs> field contains a comma-separated list of lexicographically sorted key/value pairs. n and g are mutually exclusive:

n= All documents with the same number will be stored close to each other. The number must be in the range [0,2^63-1]. Just like n=, but with a string instead of number.
The modifiers should only be used in cases where document co-localization improves performance. Examples are visiting and streaming search touching a subset of the data. Read more about document to bucket distribution.

For instance, schemes specifying a groupname, will have the LSB bits of the location set to a hash of the groupname. Thus all documents belonging to that group will have locations with similar least significant bits, which will put them in the same bucket. If buckets end up split far enough to use more bits than the hash bits overridden by the group, the data will be split into many buckets, but each will typically only contain data for that group.

user-specifiedRequiredA unique ID string
Find examples in album-recommendation. In most cases, the Vespa instance is not shared and hence no use for a namespace - here namespace is set to the same as the document type:
• Uniform distribution: id:mynamespace:music::mydocid-123
• Data access is grouped, e.g. personal data (each user has a numeric user id): id:mynamespace:music:n=12345:mydocid-123
• Using a string identifier to group data: id:mynamespace:music:g=mymusicsite.com:mydocid-123
Access documents using /document/v1/:
$curl http://hostname:8080/document/v1/mynamespace/music/docid/mydocid-123$ curl http://hostname:8080/document/v1/mynamespace/music/number/12345/mydocid-123