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Difference between Data Fragmentation & Index Fragmentation


Difference between Data Fragmentation & Index Fragmentation

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Shadab Shah
Shadab Shah
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Hi all,

I am a newbie in SQL Server. I was exploring fragmentation topic. i came across two term which were most confusing to me and i tried to find out are those 2 term different or same.

This 2 terms are 'Index Fragmentation' & 'Data Fragmentation'. There name are sufficient to tell me that they mean fragmentation while indexing & storing data. Does other than this they mean something.
SQLisAwE5OmE
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Shadab Shah (1/3/2013)
Hi all,

I am a newbie in SQL Server. I was exploring fragmentation topic. i came across two term which were most confusing to me and i tried to find out are those 2 term different or same.

This 2 terms are 'Index Fragmentation' & 'Data Fragmentation'. There name are sufficient to tell me that they mean fragmentation while indexing & storing data. Does other than this they mean something.


I believe both means the same. Fragmentation occurs when loss of allocation order of data pages happens. So, in terms of index fragmentation, it means when the loss of allocation order of data pages at the leaf node level of the index.

I would wait for experts opinion on this. What I mentioned above is my understanding.

SueTons.

Regards,
SQLisAwe5oMe.
GilaMonster
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Never heard the term 'data fragmentation'. Guess the person meant index fragmentation, because data can only be fragmented when it's in an index. (unless they meant data file fragmentation, which is an OS thing)


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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Shadab Shah
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yup w00t It was Data File Fragmentation. Can you please refer me some resource which can give me practical & theoretical knowledge about Data File Fragmentation wrt SQL Server.
GilaMonster
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Since it's not usually a major issue, and can't be fixed while SQL's running, and it pretty immaterial on a SAN, not really.

But it you want. Google: file system fragmentation
It's not a SQL thing, it's an OS thing.


Gail Shaw
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Shadab Shah
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Hi,
Again found a new term as 'Table Fragmentation'. Now this term makes sense to me , because consider one table having clustered index on one column. The content of this column would be stored in B-Tree format and then when the page is full it allocates............. This stuff is know as Index Fragmentation.

Now what about the column other than the clustered index. They too might have fragmentation. Does this means Table Fragmentation.
GilaMonster
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Shadab Shah (1/4/2013)
Now what about the column other than the clustered index. They too might have fragmentation. Does this means Table Fragmentation.


No. Fragmentation is something that indexes have, not tables.

Fragmentation is the difference between logical and physical order. Columns that are not part of an index key have no logical ordering, hence can't be fragmented.


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

We walk in the dark places no others will enter
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