What is index fragmentation in database?
SQL Server index fragmentation is a common source of database performance degradation. Fragmentation occurs when there is a lot of empty space on a data page (internal fragmentation) or when the logical order of pages in the index doesn’t match the physical order of pages in the data file (external fragmentation).
What is fragmentation report?
It indicates how dense the pages in your index are, i.e. on average how full each page in the index is (internal fragmentation). The higher the number the better speaking in terms of fragmentation and read-performance.
How much does index fragmentation affect performance?
Index Fragmentation Can Hinder Performance As you insert data into a table, if the data is under the SQL Server’s data page size, then SQL Server will allocate one page to store that data. Otherwise, SQL Server will allocate multiple pages to store the data, and these data pages are often not full.
How does index fragmentation affect performance?
Index Fragmentation Can Hinder Performance As you insert data into a table, if the data is under the SQL Server’s data page size, then SQL Server will allocate one page to store that data. As SQL Server scans the index, it needs to do 20% more work by processing 1,200 pages instead of the original 1,000.
What is index in SQL Server?
An index is an on-disk structure associated with a table or view that speeds retrieval of rows from the table or view. These keys are stored in a structure (B-tree) that enables SQL Server to find the row or rows associated with the key values quickly and efficiently.
What is a good fragmentation percentage?
There’s no hard and fast rule about how fragmented your drive should be before you defrag it. You might want to keep your fragmentation percentage under 5% or so, however, so that the defragmentation process doesn’t take too long to finish.
Is there a report for SQL index fragmentation?
ApexSQL Defrag provides us with a number of reports that shows statistical information about the database indexes. These reports can be configured and checked under the Reports tab below: The first report is the Total report, that shows a graphical representation for SQL index fragmentation and disk space usage at the selected level.
How to get the fragmentation percentage of a database?
In order to get meaningful information about the fragmentation percentage of all indexes under the specified database from the sys.dm_db_index_physical_stats DMF, you need to join it with the sys.indexes DMV, as in the T-SQL script below:
When does fragmentation start to occur in an index?
When indexes are first built, little or no fragmentation should exist. Over time, as data is inserted, updated, and deleted, fragmentation levels on the underlying indexes may begin to rise. So let’s see how it happens. When a page of data fills to 100 percent and more data must be added to it, a page split occurs.
When does external fragmentation occur in SQL Server?
External fragmentation – External, a.k.a logical, fragmentation occurs when an index leaf page is not in logical order, in other words it occurs when the logical ordering of the index does not match the physical ordering of the index. This causes SQL Server to perform extra work to return ordered results.