Hi Paul, great article as usual. I have a somewhat off-topic question. It seems to me that all other indexes are a waste of cycles. True this DMV is reset periodically but results could be archived periodically. You have to consider the overall perf hit from fragmentation when deciding which indexes to take care of. Thanks Paul. I have one doubt. Can you please confirm me reorganize is single thread operation regardless of sql server version and edition or it could be multi thread somehow?.
The same is with rebuild process, Rebuild is multi thread in enterprise editions only and single thread in all other editions. Great article, thanks for that. Thanks a million. Abort means a query was killed for some reason. I have some indexes in SQL Server that are small. That is less than 10 pages. It appears that these are not rebuilt since they appear to keep their fragmentation level regardless of which method I use to defragment them.
Is it right if I say the reason for this time difference maybe for parallel rebuild indexes vs single reorganize indexes or synchronous alwayson? Any suggestion on what to check in that scenario? Log file is not growing like crazy. Index reorganization is a process where the SQL Server goes through the existing index and cleans it up. Index rebuild is a heavy-duty process where an index is deleted and then recreated from scratch with an entirely new structure, free from all piled up fragments and empty-space pages.
While index reorganization is a pure cleanup operation that leaves the system state as it is without locking-out affected tables and views, the rebuild process locks the affected table for the whole rebuild period, which may result in long down-times that could not be acceptable in some environments.
But reorganizing index is much better from the efficiency standpoint since it does not lock the affected indexed table during the course of operation. Servers with regular maintenance periods e. Provide appropriate database and table details and execute following code in SQL Server Management Studio to reorganize all indexes on a specific table:. Provide appropriate database and table details and execute following code in SQL Server Management Studio to rebuild all indexes on a specific table:.
Internal fragmentation is you have a high percentage of free space on your index pages, meaning that SQL Server needs to read more pages when scanning the index. External fragmentation is when the pages of the index are not in order any more, so SQL Server has to do more work, especially in IO terms to read the index.
If your indexes become too fragmented, at best, your queries will be less efficient but at worst, SQL Server will just stop using the indexes all together, meaning virtually all queries would have to perform a table scan or clustered index scan. This will hurt your performance a lot! When you reorganise an index, then SQL Server uses the existing index pages and just shuffles data around on those ages. This will alleviate internal fragmentation and can also remove a small amount of external fragmentation.
It is a lighter weight operation than rebuild and is always online. When you rebuild an index, SQL Server actually resorts the data of the index and uses a new set of index pages.
This will obviously alleviate both internal and external fragmentation but is a more heavy weight operation and by default causes the index to go offline, although it can be performed as an online operation, depending on your SQL Server version and settings.
Please do not expect to have 0 fragmentation after a Rebuild however. Unless you use a MAXDOP query hint, SQL Server will parallelise the rebuild operation and the more processors involved, the more fragmentation there is likely to be, because each processor or core, will rebuild their section or fragment of the index individually, without regard for each other. This is a trade off between best fragmentation levels and time taken to rebuild the index.
Sign up to join this community. Those are also havy fragmented indexes and they should be rebuild. The second DMV is sys. As before, use the code from below and run it against a targeted database.
I got nothing on my sample database, so I ran it against another one with actual traffic:. What this query will essentially do, is help us analyze unused SQL indexes same as before, just a minor change in Where clause to only grab user tables. Furthermore, this will find seeks, scans, lookups, and updates of an index:. The major part here is seeks and scans. The rule of thumb is that the scans are bad, seeks are good. Whenever you see seeks, it basically means that the SQL index is being used.
It also means that it makes effective use of an index. On the other side, when scans are present is also means that indexes are being used just not as effective as within seeks because it had to go through the entire index to find what it needed. The bottom line here is that if you find SQL indexes with a low number of seeks and scans, it means that they are not being used except for cases when they just have been created.
As can be seen in the figure above, we have quite a few indexes with a low number of seeks and scans, even zeros.
I want to wrap thing up with another solution that could really help you in the real world. I hope this article on SQL index maintenance has been informative and I thank you for reading. FragTestSequential ID ;. Name ,. SomeData ,. GO FROM sys. AND ixs. WHERE ixs. Author Recent Posts.
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