Special Fields

This document describes the special fields supported by Rockset.

_id

  • Field _id determines a unique identifier for each document within a collection.
  • If _id is not specified in a document, it is automatically generated by Rockset as a uuid.

_meta

  • _meta is a nested field which provides a variety of metadata information about each document.
  • Currently, _meta holds information about the source from which document was inserted into the collection. For eg. the bucket name and path incase of S3.
  • Rockset ignores _meta field and its value for all the documents that are inserted into a collection.

_event_time

  • Rockset allows a user to map a time field in an event dataset to Rockset's _event_time field at the time of collection creation.
  • All queries on _event_time are significantly faster than similar queries on regular indexed fields.
  • A user can map fields with following time formats:
    • milliseconds
    • seconds
  • Rockset supports IANA time zone values.
  • Internally Rockset stores _event_time in microseconds.

Querying special fields:

> SELECT _id, _meta, _event_time FROM my-collection LIMIT 5;
+-------------------------------------------------------------------------------------+----------------+--------------------------------------+
| _meta                                                                               | _event_time    | _id                                  |
|-------------------------------------------------------------------------------------+----------------+--------------------------------------|
| {'s3': {'bucket': 'my-collection', 'offset': 0, 'path': '47304-1709397620935'}}     | 1535068823524  | 5d99f42c-44ec-2024-a032-ac14d1cbf44d |
| {'s3': {'bucket': 'my-collection', 'offset': 0, 'path': '46242-1709397472272'}}     | 1535068823426  | e5d4c136-8d56-ac39-38f5-2f795ae38007 |
| {'s3': {'bucket': 'my-collection', 'offset': 0, 'path': '46242-1503238554088'}}     | 1535068823326  | 71df712e-04bc-7c9b-0114-97b19741b215 |
| {'s3': {'bucket': 'my-collection', 'offset': 0, 'path': '47302-1151051235692'}}     | 1535068822852  | 517412d2-1a23-1b49-fc3b-441c630ed4ff |
| {'s3': {'bucket': 'my-collection', 'offset': 0, 'path': '45189-1709397393868'}}     | 1535068822527  | d16bf924-f758-21db-c832-4a25323b2938 |
+-------------------------------------------------------------------------------------+----------------+--------------------------------------+
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