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May 4th

Question and Answer

Connor McDonald

Thanks for the question, Bb.

Asked: February 08, 2019 - 11:37 pm UTC

Last updated: February 14, 2019 - 4:25 am UTC

Version: 6

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2. The airline database is an active database. The admin of the database has configured the redo log buffer to 16M. Assume that, in every 1/2 second 1M of redo log entries are created. LGWR copies those entries from buffer to file when 1M full in 1 second.

At any point of time how much of redo log buffer is used? What do you do, for effective utilization of redo log buffer?


and Connor said...

There are a LOT of moving parts in the log writer nowadays. We have

- shared access to the redo log buffer (effectively log buffer parallelism),
- private redo buffers

so the days of diagrams of "here's my log buffer, that gets written at 1M full" are still in the main true, but a vast simplification of what is really happening.

Unless you are regularly seeing significant 'log buffer waits' in your AWR reports, or other monitoring of system-wide wait events, then there is normally no need to touch the log buffer settings.



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Comments

harry, February 13, 2019 - 6:43 am UTC

yes, day to day I see 'log buffer waits' in your AWR reports but what is another way tune this wait event?
Connor McDonald
February 14, 2019 - 4:25 am UTC

yes, day to day I see 'log buffer waits' in your AWR reports


And what *time* and *percentage* of time lost is due to log buffer waits?


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