Informix Error -638

Reasons / Common Causes

-638 fires when CREATE OPTICAL CLUSTER names a TEXT/BYTE column that's actually stored in an ordinary storage space rather than on optical media — per the official guidance, an optical cluster can only be created on TEXT/BYTE columns that are themselves stored on optical media.

1. The named column stored in an ordinary dbspace/blobspace rather than an optical storage space, per the official guidance — the direct, only cause.
2. A column-naming mistake, per the official guidance's suggested check — confirming the statement doesn't accidentally name a TEXT/BYTE column stored in a regular storage space.

Solutions / Resolution

1. Check that the statement doesn't name a TEXT/BYTE column stored in a storage space, per the official guidance, rather than on optical media.
2. Confirm which storage space the column actually uses:

   SELECT colname FROM syscolumns
   WHERE tabid = (SELECT tabid FROM systables WHERE tabname = 'documents');
   

   combined with reviewing the CREATE TABLE's original IN storage-space-name clause for that column, to confirm whether it targets optical media or an ordinary storage space.
3. If optical clustering is genuinely needed for this data, recreate the column so it's stored on optical media, since a column already committed to an ordinary storage space can't simply be optically clustered in place.

Examples

The disallowed attempt

-- content is TEXT, stored in an ordinary blobspace (not optical media)
CREATE OPTICAL CLUSTER doc_cluster ON documents (content) ...;
-- -638: content isn't stored on optical media

Diagnostic Checks

1. Review the CREATE TABLE statement's storage-space clause for the target column, confirming whether it was defined to live on optical media or an ordinary storage space.
2. Check with the storage-space's administrator/configuration if it isn't obvious which storage spaces are backed by optical media on this instance.

Related Errors / Related Topics

• -631 — "Cannot create optical cluster on column that is not TEXT or BYTE." A related optical-cluster restriction, on the column's data type rather than which storage medium it's stored on.
• -606 — "Invalid storage-space name for TEXT or BYTE data." A related storage-space error, about an invalid/nonexistent name rather than the right kind of storage space (optical vs. ordinary).

The column is the right type but the wrong storage medium — confirm which storage space it actually lives in before attempting an optical cluster.