Friday, 29 August 2014

Wait Event: Latch Free Waits

Wait Event: Latch Free Waits

Possible Causes:

  • This wait indicates that the process is waiting for a latch that is currently busy (held by another process).
  • When you see a latch free wait event in theV$SESSION_WAIT view, it means the process failed to obtain the latch in the willing-to-wait mode after spinning _SPIN_COUNT times and went to sleep.
  • When processes compete heavily for latches, they will also consume more CPU resources because of spinning. The result is a higher response time
Actions:
  • If the TIME spent waiting for latches is significant then it is best to determine which latches are suffering from contention.

Ref:

  • A latch is a kind of low level lock.
  • Latches apply only to memory structures in the SGA. They do not apply to database objects. An Oracle SGA has many latches, and they exist to protect various memory structures from potential corruptionby concurrent access.
  • The time spent on latch waits is an effect, not a cause; the cause is that you are doing too many block gets, and block gets require cache buffer chain latching


FAQ: What are Latches and What Causes Latch Contention (Doc ID 22908.1)
Database Lock and Latch Information Knowledge Browser Product Page (Doc ID 267887.1)
gavinsoorma.com

No comments: