Error code

Oracle ORA-01555

ORACLEORA-01555
Database Error Code· An error code returned by a database server such as PostgreSQL or MySQL.

What it means

snapshot too old — the undo segment needed to reconstruct an old version of a row has been overwritten.

How to fix it

  1. Increase the UNDO_RETENTION parameter to retain undo data longer.
  2. Use the GUARANTEE RETENTION option on the undo tablespace if undo space allows.
  3. Optimize or break up long-running queries so they complete before undo is recycled.

Not affiliated with Oracle. Answer summarized from the manufacturer's manual linked above; consult that source for the authoritative procedure.