Oracle reports negative deltas on cumulative stats
This is a bug in Oracle stats tables on PDB's were for some reason, stats are "stolen" from a PDB instance and incorrectly reported on the SEED instance. During the next poll, the stats are "moved back" to the PDB stats. This causes a huge spike when calculating a delta, first a negative and directly followed by a positive spike. On average, the numbers are still correct, but plotting these values creates problems. Seems this occurs more frequently on Heavy loaded instances, and only affects PDB's on a CDB (Oracle Multi Tenant). The error occurs both in the PDB version of sysstat tables and the PDB's own "virtual" sysstat table. It does not occur in the CDB's own systat table s the totals are correct, the error is only the internal "distribution" of the stats between the existing PDB's.