Troubleshooting ‘Log File Sync’ Waits

I have been contacted by one of our customers to provide reference information on troubleshooting Oracle Log File Sync waits.

I think that this information worth short blog post.

Reasons:

  • Log File Sync waits occur when sessions wait for redo data to be written to disk
  • typically this is caused by slow writes(IO subsystem saturation,…)
  • spikes in Log File Parallel Write, as shown by James Morle
  • or the application is committing too frequently
  • improper Operating System configuration(check 169706.1)
  • CPU overburning(very high demand => LGWR on run queue, check Kevin Closson post)
  • high Log Parallelism, which saturates filesystem/OS, as investigated by Nikolay Savvinov
  • BUGs in Oracle(especially with RAC option) and 3rd Party software(like ODM/DISM)

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Production System with Performance Problems

Hi.

Recently I was involved in performance troubleshooting of one quite expensive system

that had performance problems during business hours.

I’ll not provide all details, but just post some pictures that will show resource usage:

Oracle memory allocation:

Linux memory allocation

or from other side:

cat /proc/meminfo
 MemTotal:     98848220 kB
 MemFree:      75109972 kB
 Buffers:        597460 kB

Continue reading