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Warning: long redo log write elapsed times detected, the LG* process tracefiles have more details

Warning: long redo log write elapsed times detected, the LG* process tracefiles have more details

This warning means LGWR / LGnn background processes are taking too long to write redo to the online redo logs.

It is usually related to one of these:

- Slow storage / high I/O latency on redo log disks
- Redo logs placed on busy disks together with datafiles, FRA, archive logs, backups, or OS files
- Too many commits from the application, causing frequent LGWR flushes
- Redo log size too small, causing frequent log switches
- CPU scheduling issue, where LGWR is not getting CPU quickly
- Data Guard synchronous transport delay, if using SYNC/AFFIRM
- In newer 19c RU versions, especially around 19.28, this warning can appear more visibly because of diagnostic changes, so first confirm whether there is a real performance impact before changing anything. - Oracle’s own wait-event documentation says log file sync is the foreground wait for redo write confirmation after commit, and log file parallel write is one of the key log-file I/O waits to investigate when average time is high.

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