logical vs physical reads

Posted on 2006-11-16
Last Modified: 2008-03-17
what is the difference between logical reads and physical reads?
Question by:yanci1179
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LVL 143

Accepted Solution

Guy Hengel [angelIII / a3] earned 300 total points
ID: 17959845
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

Author Comment

ID: 17959911
i read that in books online....but it didn't really mean much.  Ideally which one should be lower?
LVL 32

Assisted Solution

bhess1 earned 200 total points
ID: 17959980
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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LVL 143

Expert Comment

by:Guy Hengel [angelIII / a3]
ID: 17960495
perfectly, the physical reads should be 0. also, logical reads as low as possible.

Author Comment

ID: 17960572
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?
LVL 32

Expert Comment

ID: 17962141
Absolutely correct.

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