DBCC dropcleanbuffers

• Subhash-63067

  SSCarpal Tunnel

  Points: 4171

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  January 17, 2005 at 8:39 am

  #162985

  Hai,

  I was trying to analyse the IO read of a query.

  i have executed the following query

  Set statistics io on

  select * from corpbonds

  set statistics io off

  and i got the message :

  Table 'CorpBonds'. Scan count 1, logical reads 21, physical reads 0, read-ahead reads 0.

  means that no physical read and the data is taken from the cache.

  After this i cleared the buffer cache

  dbcc dropcleanbuffers

  executed the same query and i got the same message like:

  Table 'CorpBonds'. Scan count 1, logical reads 21, physical reads 0, read-ahead reads 0.

  What is means, according to my knowledge after clearing the cache the query should take the data from the disk and hence the Phycal read should be greater that zero right ?

  Can anybody explain this?

   

  
  subban

• January 20, 2005 at 8:00 am

  This was removed by the editor as SPAM

• Chandra-149818

  SSC Enthusiast

  Points: 130

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  January 27, 2005 at 8:33 am

  #539346

  DBCC dropcleanbuffers command only removes clean buffers, not dirty buffers.

  Before running the DBCC DROPCLEANBUFFERS command, you may first want to run the CHECKPOINT. Running CHECKPOINT will write all dirty buffers to disk.

  Now you should see the difference.....