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Page Splits And Fill Factor Expand / Collapse
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Posted Sunday, October 10, 2010 2:04 AM
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Page Splits
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When page split happens - which part of the row is moved? Is the whole row copied to a new location [or] that part of the row which cannot be accommodated is copied over?.

Fill Factor
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"Page spilts will be reduced by specifying fill factor"

This is something I read and got confused thinking about the inserts and updates. There is a certain % of space that will be reserved on setting the fill factor (Okay accepted !!). But, Is the space reservation applied only when entering the data for the first time in the page?

Will the reservation space be consumed while updating and inserting new records? Is this how fill factor help in update and insert.




Post #1001782
Posted Sunday, October 10, 2010 1:07 PM


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For a good discussion of why page splits occur and what happens, read the following (It contains sample code and results to make understanding much easier)

http://sqlblogcasts.com/blogs/tonyrogerson/archive/2007/06/28/what-is-a-page-split-what-happens-why-does-it-happen-why-worry.aspx

The above blog also contains this link, (to a Paul Randal blog post) which further explains (with sample code) what occurs / causes page splits.
http://blogs.msdn.com/b/sqlserverstorageengine/archive/2006/12/13/more-undocumented-fun_3a00_-dbcc-ind_2c00_-dbcc-page_2c00_-and-off_2d00_row-columns.aspx

Corrected spelling of Paul Randal's name


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Post #1001835
Posted Sunday, October 10, 2010 7:50 PM
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Thank you

According to the blog .. The complete row is transferred to the new page. But it still does not answer my question about the Fill Factor. May be I need to do more study on this topic.

Anyways, Thanks again for the reply.

Post #1001871
Posted Tuesday, October 12, 2010 6:24 AM


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The fill factor only applies when an index is created or rebuilt.

SQL server does not try to maintain the fill factor when updating or inserting values.

Quote from BOL:

The fill factor setting applies only when the index is created, or rebuilt. The SQL Server Database Engine does not dynamically keep the specified percentage of empty space in the pages. Trying to maintain the extra space on the data pages would defeat the purpose of fill factor because the Database Engine would have to perform page splits to maintain the percentage of free space specified by the fill factor on each page as data is entered.
Post #1002727
Posted Tuesday, October 12, 2010 11:55 AM
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Excellent ! Just the answer I was looking for. Thank you steven.

Here is an extract from microsoft url about the fill factor.
http://msdn.microsoft.com/en-us/library/aa196711(SQL.80).aspx
Post #1003081
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