Row-ID Descriptor

A particular row identifier can appear in multiple fragments. For example, row 1 in fragment A describes a different customer than row 1 in fragment B. The unique fragment identifier enables the database server or access method to locate the correct row 1.

A secondary access method sets these values in a row-ID descriptor, or MI_AM_ROWID_DESC structure, during an index scan. The following functions set data in the row-ID descriptor.

Accessor Function

Value Set

mi_id_setrowid()

The row identifier

mi_id_setfragid()

The fragment identifier

The database server fills the row-ID descriptor when it calls:

• am_insert or am_delete to add or delete a table row
• am_insert to build a new index
• am_insert and am_delete in response to an ALTER FRAGEMENT command

The following accessor functions extract information from the descriptor.

Accessor Function

Return Value

mi_id_rowid()

The row identifier

mi_id_fragid()

The fragment identifier

The following system catalog information describes a fragment identifier:

• The partnum attribute in the systables system catalog table
• The partn attribute in the sysfragments system catalog table

For detailed information about system catalog tables, refer to the IBM Informix: Guide to SQL Reference.