Informix Error -9831: Could not find opclass id opclass_ID while resolving compare routine for index.

Reasons / Common Causes

-9831 fires when the operator class for one or more key parts of an index no longer exists in the database — per the official guidance.

1. The operator class backing an index key part having been dropped, per the official guidance — the direct, only cause; the index is no longer valid.

Solutions / Resolution

1. Drop the index, per the official guidance — it can no longer be used once its operator class is gone.

Examples

Dropping the invalid index

DROP INDEX my_index;

Diagnostic Checks

1. Check the system catalog for the operator class ID named in the error, confirming it no longer exists, and drop the affected index.

Related Errors / Related Topics

• -9832 — "Could not find routine routine_name while resolving compare routine." A related index-corruption error, on a missing comparison routine rather than a missing operator class.
• -9833 — "Could not find extended type type_ID for index." A related index- corruption error, on a missing extended type rather than a missing operator class.

The index's operator class no longer exists — drop the index.