Craig Shallahamer's Blog
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You were brought to this page based on an internet search
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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>Figure 6-12. Some of the output of OSM clone script, clone.sql. Notice this figure shows only the last page (page 93), which means there are many buffers with clones, but none with more than six.
p><p>Not only does its free buffer search algorithm favor replacing cloned buffers, but Oracle tries to limit the number of clones per buffer. Oracle wants the number of clones per buffer to not exceed the hidden instance parameter _db_bock_max_cr_dba, which has a default value of 6. However, if the cloning situation becomes intense, a buffer can easily have more than six clones.
p><p>But what if file number 9, block number 3755 in Figure 6-12 had 120 clones, rather than 6? If the system were experiencing CBC latch contention along with the 120 clones, we would be motivated to find out what's so special about this block and why so many processes are interested in accessing it.
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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