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Vivek's SQL Notes

Vivek johari is currently a Analyst and have more that 5.5 yeras of experience in database. He has Master degree in Computer and also he is Microsoft certified Sql DBA (MCTS)& Microsoft certified SQl BI professional(MCTS). He is also Oracle certified profession(OCP)DBA in ORACLE 10g and ORACLE 9i.He has the experience of working in PL/SQL, T-SQL and SSIS/SSRS. His work basically involved designing and optimization of the Database.He has also published many database articles on his blog Technologies with Vivek Johari.

Rebuild And Reorganization of Indexes

Rebuild and  Reorganization of Indexes:- SQL Server has the ability of maintaining the indexes whenever we makes changes (update, Insert, Delete) in the tables. Over a period of time, the may causes the fragmentation on the table in which  the logical ordering based on the key value pairs does not match with the physical ordering inside the data files. This causes the degradation of the performance of the SQL Query.To solve this problem of fragmentation, we use rebuilding or reorganization of the indexes.

In case of Rebuilding, it drop the particular index and again recreate it.It removes fragmentation, reclaims the disk space by compacting the pages based on the specified or existing fill factor setting, and again reorders the index rows in those contiguous pages. We can rebuild all the indexes of the table within a single transaction by specifying the ALL with it.


ALTER INDEX [Indexname] ON [tablename] REBUILD

ALTER INDEX ALL ON [tablename] REBUILD

In case of Reorganization, it defragments the leaf level nodes of indexes by physically reordering the leaf-level pages to match the logical, left to right, order of the leaf nodes.  It uses minimal system resources and also compact the index pages

ALTER INDEX [Indexname] ON [tablename] REORGANIZE

ALTER INDEX ALL ON [tablename] REORGANIZE

Rebuild should be used when the fragmentation index is greater than 30% and reorganization option should be used when the fragmentation index is between 5% and 30%. Rebuilding of an Index can be done online or offline. But to achieve the availability of the index, rebuilding should be done online. Reorganization can be done online.


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