X DevAPI relies on server based document ID generation, added
in MySQL version 8.0.11, which results in sequentially
increasing document IDs across all clients.
InnoDB uses the document ID as a
primary key, therefore these sequential primary keys for all
clients result in efficient page splits and tree
This section describes the properties and format of the automatically generated document IDs.
_id field of a document behaves in the
same way as any other field of the document during queries,
except that its value cannot change once inserted to the
_id field is used as the
primary key of the collection (using stored generated
columns). It is possible to override the automatic generation
of document IDs by manually including an ID in an inserted
If you are using manual document IDs, you must ensure that IDs from the server's automatically generated document ID sequence are never used. X Plugin is not aware of the data inserted into the collection, including any IDs you use. Thus in future inserts, if the document ID which you assigned manually when inserting a document uses an ID which the server was going to use, the insert operation fails with an error due to primary key duplication.
_id field value is not present
in an inserted document, the server generates an
_id value. The generated
_id value used for a document is returned
to the client as part of the document insert
Result message. If you are using X DevAPI
on an InnoDB Cluster, the automatically generated
_id must be unique within the cluster. Use
option to ensure that the
part of the document ID is unique to the cluster.
_id field must be sequential (always
incrementing) for optimal InnoDB insertion performance (at
least within a single server). The sequential nature of
_id values is maintained across server
In a multi-primary Group Replication or InnoDB Cluster
environment, the generated
_id values of a
table are unique across instances to avoid primary key
conflicts and minimize transaction certification.
This section describes how document IDs are formatted. The
general structure of the collection table remains unchanged,
except for the type of the generated
column, which changes from
The format of automatically generated document ID is:
|4 bytes||8 bytes||16 bytes|
serialis a per-instance automatically incremented integer serial number value, which is hex encoded and has a range of 0 to 2**64-1. The initial value of
serialis set to the
auto_increment_offsetsystem variable, and the increment of the value is set by the
start_timestampis the time stamp of the startup time of the server instance, which is hex encoded. In the unlikely event that the value of
start_timestampis incremented by 1 and the
serialvalue then restarts at 0.
unique_prefixis a value assigned by InnoDB Cluster to the instance, which is used to make the document ID unique across all instances from the same cluster. The range of
unique_prefixis from 0 to 2**16-1, which is hex encoded, and defaults to 0 if not set by InnoDB Cluster or the
mysqlx_document_id_unique_prefixsystem variable has not been configured.
This document ID format ensures that:
The primary key value monotonically increments for inserts originating from a single server instance, although the interval between values is not uniform within a table.
When using multi-primary Group Replication or InnoDB Cluster, inserts to the same table from different instances do not have conflicting primary key values; assuming that the instances have the
auto_increment_*system variables configured properly.