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 FRAGMENT 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, see the Informix® Guide to SQL: Reference.