Issue

An ongoing query fails and the 21003 error occurs indicating the snapshot is too old to read.

Note
The 21003 error is not related to data corruption or loss.

Cause

This occurs when the Undo Segment is too small relative to the workload.

Also, since Undo space is overwritten space, this error indicating the snapshot is too old occurs when past data cannot be read.

Caution
If UNDO_RETENTION is set excessively high, UNDO reuse may not be possible.

Set the UNDO_RETENTION parameter appropriately to be greater than the time taken by the longest-running transaction.

Expand the Undo space sufficiently.

Related to