buffer busy waits

A buffer busy wait occurs if multiple processes want to access a buffer in the buffer cache concurrently.

The type of buffer that causes the wait can be queried with v$waitstat. v$waitstat lists the waits per buffer type for buffer busy waits only. Therefore, the following SQL statement always returns 0

select
  (select total_waits from v$system_event
  where event='buffer busy waits')
-  /* minus */
  (select sum(count) from v$waitstat)
from
  dual;

• segment header:
  Problem: probably a freelist contention.
• data block:
  
• undo header:
  Problem: too few rollback segments (if not using undo tablespaces)
• undo block:
  Problem: too small rollback segments (if not using undo tablespaces)

Buffer busy waits is one of the events that Oracle records while it is running.