WAIT STATISTIC NOTES:
  • Class - Class of block subject to contention
  • Count - Number of waits by this OPERATION for this CLASS of block
  • Time -Sum of all wait times for all the waits by this OPERATION for this CLASS of block

  • Data Blocks - Usually occurs when there are too many modified blocks in the buffer cache; reduce contention by adding DBWR processes.
  • Free List - May occur if multiple data loading programs run simultaneously.
  • Segment Header - May occur when may full table scans execute simultaneously with data loading processes; aggravated by the parallel options. Reschedule data loading jobs to reduce contention;
  • Sort Block - Rarely seen except when the Parallel Query option is used; reduce contention by reducing the degree of parallelism or decreasing the SORT_AREA_SIZE init.ora parameter setting.
  • Undo Block - Very rarely occurs; may be caused by multiple users updating records in the same data block at a very fast rate; contention can usually be resolved by increasing the PCTFREE of the tables being modified.
  • Undo Header - May occur if there are not enough rollback segments to support the number of concurrent transactions.