Craig Shallahamer's Blog
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The text below is an except from the book,
Oracle Performance Firefighting, written by
Craig Shallahamer of
OraPub, Inc.
Figures and tables are not included on this page, only their reference.
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©2009, 2010 by Craig Shallahamer. This is copyrighted material.
Please—Out of respect for those involved in the creation of the book and also for
their familes, we ask you to respect the copyright both in intent and deed. Thank you.
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<p>A challenge in effectively dealing with log file sync waits is that there are many causes for this wait event. For example, it can occur because of rapid application commits (there is overhead in each commit request), the log writer has too much redo to write per commit (requiring more time to complete each write), or large amounts of redo per transaction (requiring more time to complete the write). Whatever the reason, the general solution is understanding the problem arises when a commit occurs and that commits are simply taking too long.
p><p>As Figure 8-7 shows, when the commit times are taking too long, it is common for other redo-related wait events to occupy the top few wait slots. The most common second top event will be log file parallel write.
p><p>Figure 8-7. Shown is OSM report swpctx.sql, which is a v$system_event wait event report. This report indicates a classic wait event situation with severe log file sync contention. Notice the second top wait event is the typical paired event, log file parallel write.
p>
©2009, 2010 by Craig Shallahamer. This is copyrighted material.
Please—Out of respect for those involved in the creation of the book and also for
their familes, we ask you to respect the copyright both in intent and deed. Thank you.
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