Informix limits the number of outstanding in-place ALTER TABLE requests to 255. A 256th in-place alter of a table was requested before the completion of the first in-place alter. Completion means that all rows of the table in the first in-place alter have been physically altered.
To recover from this error, you must take one of the following steps:
* Wait until the first in-place alter is complete, and issue another in-place ALTER TABLE statement.
* Change the format of the ALTER TABLE statement to request an alter that does not add columns to the end of the table. Such a statement will use the older algorithm instead of the in-place alter algorithm.
* Perform an update of each row in the table to force the outstanding alters to complete. Because rows are only modified to the latest schema as they are updated, the only way to force an in-place alter to complete physically is to update each row in the table. To accomplish this result, use a dummy update in which a column in the table is set to its own value. The dummy update forces the row to be updated to the latest schema in the process without actually changing column values. Rows are always altered to the latest schema, so a single pass through the table that updates all rows will complete all outstanding in-place alters.