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by Craig Shallahamer Get the book here |
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Craig Shallahamer's Blog
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. To order the book in either print or PDF form, click here. ©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. ------------------------------- And finally, don't let anyone tell you that once you've hit latching contention, you can't do anything more. As this book is beginning to reveal, there is a very diverse and practical set of solutions to each latch and mutex contention scenario. 1 Each Oracle table has an associated high water mark. Going from bottom (row one) to top, the high water mark points to the topmost block that has ever contained a row. When performing a full table scan, Oracle processes know never to scan above the high water mark-it just doesn't make sense to do so. The high water mark is stored in both Oracle's data dictionary and in the table's header block. If you do a block dump on a table's header block, the high water mark is very plainly shown. 2 I am in no way implying Oracle sincerely cares about how much memory its database system requires. 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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