The Change Table schema has two parts: metadata fields to tie the change table to the original record, and column data specified by the policy definition.

The metadata portion of the change table contains the fields described in the table that follows.

Table 1. Change table metadata
Field Size Description
_Tran-Id integer Transaction number used to create this record.
_Time-Stamp timestamp tz UTC timestamp and zone of the database server.
_Change-Sequence int64 Number indicating an operation’s capture order within an object.
_Continuation-Position integer Support for larger than 32K record sizes.
  • 0 — no continuation
  • Nonzero indicates last successfully processed field.
_ArrayIndex integer Used in conjunction with _Continuation-Position to identify an element of an array field.

If a Non-zero value, it is the array index of the element.
_Fragment integer This value means a fragmented field is either present or not.
  • 0 —This field is not split into 2 records.
  • 1 — This field is split into 2 records.

The remainder of the record, the column data, is defined by the source table fields defined in the CDC policy. The general format is as follows:

User Data Columns specific to Source Table. The name of the field is taken from the Source table field that was selected. Source Field Data type Value from Source Table at the time of capture

The indexes for the Change Tracking tables are described in the following table.

Table 2. Change Table indexes
Index Name Index Field Attribute Description
_Change-Sequence-Id 1 _Change-Sequence

2 _Operation

3 _Continuation

Unique

Primary

 A CDC mandated index to establish a (foreign key) relationship to the Change Tracking Table. This index provides easy access to a chain of change records through the _Change-Sequence field.
_Identifying-Fields 1 User Defined Column

Through

15 User Defined End Column

2 _Change-Sequence

Non Unique Optional index created when the policy is defined and fields are picked to become part of the the identifying field index (_Identifying-Fields). This index is completely defined when the policy is designed, including index component order. A final component is added to the identifying field index, the _Change-Sequence field to preserves order.
_Time-Sequence 1 _Time-Stamp

2 _Change-Sequence

 Non Unique A CDC mandated index that allows access to the Change Table through a combination of change sequence and a timestamp. This index promotes time sequencing of changes within a table (object).