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logical vs physical reads

Posted on 2006-11-16
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what is the difference between logical reads and physical reads?
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Question by:yanci1179
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Guy Hengel [angelIII / a3] earned 300 total points
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physical reads means the data has been read from disk into memory
logical reads means the the data was already in memory

1 logical reads means 1 page of data, ie 8KB
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by:yanci1179
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i read that in books online....but it didn't really mean much.  Ideally which one should be lower?
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by:bhess1
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In a perfect world, physical reads would be equal to the number of data blocks in your database, and all other reads would be logical.  So, by preference logical reads should be the higher of the two.
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by:Guy Hengel [angelIII / a3]
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perfectly, the physical reads should be 0. also, logical reads as low as possible.
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by:yanci1179
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let me see if I understand this logical data read from what is already in cache.  if it's not there then it has to read the physical tables and retrieve the data?
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by:bhess1
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Absolutely correct.
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