The Export / Import schema statistics procedure included here best suit 8i, 9i databases where dbms_stat.export_schema_stats may fail with some objects, leaving the stats export incomplete.
A case where a production database process suddenly experiences a drastic performance degradation may be related to changes on the information available for the optimizer.
I have seen several times that restoring previous statistics has solved this kind of problem.
That was the case yesterday when a critical department was not able to work for several hours, until older statistics were restored .
This problem also raises the issue of having a source of the previous statistics available for use. Exporting the statistics out to an export file before running the cyclic statistics gathering job can be added to the DBA toolkit.