November 10, 2012 at 7:55 am
SQLSACT (11/10/2012)
Are these clean pages or clean buffers?
Thanks
these are clean pages. SQL Server only drops pages from the buffer if there is not enough memory (or the server is restarted or you manually drop the cache). otherwise SQL Server holds the pages in memory for the next time they are accessed. that way the next query that is run the server wont have to read those pages from disk again. if the database is smaller than the ram on the system eventually the entire database may sit in memory and there is very little reading from disk. if the database is larger than the amount of ram on the system SQL Server has a very well designed algorithm for figuring out which pages have not been accessed in a while.
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November 10, 2012 at 7:56 am
SQLSACT (11/10/2012)
Does this mean that it removes the contents of the page?
No. I already told you more than once what happens when checkpoint writes a page. I'm pretty sure I've also told you the definition of 'clean page' more than once, to start with...
They just write the changes back to disk so that the pages are considered clean.
That doesn't say 'clear', 'empty', or 'discard' anywhere.
Please go and read some of the material that I and others have referred you to, Kalen's book especially
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability
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