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Data Page Allocations


Data Page Allocations

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Sean Pearce
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Comments posted to this topic are about the item Data Page Allocations



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Lokesh Vij
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Nice question Sean. Thanks for reminding the basics!

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Hugo Kornelis
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Basics? That's not how I would describe it! w00t

Thanks for a good question, Sean. I think I once read or heard that after deleting all rows from a page, a cleanup process will eventually free up the page. But I am not sure; in fact, the more I think about it, the more I start to think I am confusing things.
Anyway, can you shed some more light on this?


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Ganesh Kamal
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How to deallocate the unused pages?
Dineshbabu
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Thanks for such a nice qstn.

Is there any way to deallocate the unsed pages remains after delete?

As well as please let me know the ways to identify is there any unused pages for particular object?

Thanks,
Dinesh.

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Sean Lange
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Great question. A bit hard to read through the formatting but is not the author's fault.

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Hugo Kornelis (12/26/2012)
Basics? That's not how I would describe it! w00t

Thanks for a good question, Sean. I think I once read or heard that after deleting all rows from a page, a cleanup process will eventually free up the page. But I am not sure; in fact, the more I think about it, the more I start to think I am confusing things.
Anyway, can you shed some more light on this?


Hugo, pages in a heap are not deallocated when deleting. This is why when using heaps you have to go back in and do some cleanup periodically.

The following is quoted from BOL. http://msdn.microsoft.com/en-us/library/ms189835%28v=sql.100%29.aspx


When rows are deleted from a heap the Database Engine may use row or page locking for the operation. As a result, the pages made empty by the delete operation remain allocated to the heap. When empty pages are not deallocated, the associated space cannot be reused by other objects in the database. To delete rows in a heap and deallocate pages, use one of the following methods.

Specify the TABLOCK hint in the DELETE statement. Using the TABLOCK hint causes the delete operation to take a shared lock on the table instead of a row or page lock. This allows the pages to be deallocated. For more information about the TABLOCK hint, see Table Hints (Transact-SQL).

Use TRUNCATE TABLE if all rows are to be deleted from the table.

Create a clustered index on the heap before deleting the rows. You can drop the clustered index after the rows are deleted. This method is more time consuming than the previous methods and uses more temporary resources.


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Nice question. :-)
Revenant
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A good question! Thanks!
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Good question.



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