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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. ------------------------------- * According to the Linux manual page, readv is a synchronous call to the operating system that requests one or more blocks from an IO device. So, we know Oracle did not find these specific blocks in its buffer cache and was forced to ask the IO subsystem for the blocks. This is commonly called a physical IO or a block read. * This is a synchronous IO call, not an asynchronous IO call. If it were asynchronous, Oracle would have issued a different system call. * Take a look at the requested block size and the number of blocks requested. If you are familiar with Oracle, you'll immediately notice that we are looking at an 8KB database, and Oracle is asking for 16 blocks at once. And you are correct if you guessed the instance parameter db_multiblock_read_count is 16! 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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