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Troubleshooting: 'Log file sync' Waits (Doc ID 1376916.1)

Last updated on APRIL 01, 2020

Applies to:

Oracle Database Cloud Schema Service - Version N/A and later
Oracle Database Exadata Express Cloud Service - Version N/A and later
Oracle Database Exadata Cloud Machine - Version N/A and later
Oracle Cloud Infrastructure - Database Service - Version N/A and later
Oracle Database Backup Service - Version N/A and later
Information in this document applies to any platform.

Purpose

The purpose of this note is to help troubleshoot issues where there are significant waits for the event 'log file sync'.

Troubleshooting Steps

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In this Document
Purpose
Troubleshooting Steps
 What is a 'log file sync' wait?
 What should be collected for initial diagnosis of 'log file sync' waits ?
 What causes high waits for 'log file sync'?
 Issues affecting LGWR's IO Performance
 Compare the average wait time for 'log file sync' to the average wait time for 'log file parallel write'.
 Recommendations
 Effect of Peaks of IO (or Bursts of IO) on 'log file sync' waits
 Check LGWR Traces
 Recommendations
 Check to see if redo logs are large enough
 Recommendations
 Excessive Application Commits
 Compare the average user commits and user rollbacks to user calls
 Recommendations
 Other Wait Events that may be relevant
 Adaptive Log File Sync
 Redo Synch Time Overhead
 Known Issues
 Other diagnostics to help analyze 'log file sync' waits?
 Data Guard and 'Log File Sync'
 Troubleshooting Other Issues
 Community Discussions
References

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