[oracle@cuug ~]$ oerr ora 01555
01555, 00000, "snapshot too old: rollback segment number %s with name \"%s\" too small"
// *Cause: rollback records needed by a reader for consistent read are
// overwritten by other writers
// *Action: If in Automatic Undo Management mode, increase undo_retention
// setting. Otherwise, use larger rollback segments
原文：http://www.cnblogs.com/iyoume2008/p/4690700.html