This script will automatically determine whether a rebuild or a reorganize should be used according to the fragmentation of the index. It will then execute the appropriate command. Note that performing index rebuilds online during production hours will cause contention. [cc lang=”sql”] SET NOCOUNT ON; DECLARE @objectid int; DECLARE @indexid int; DECLARE @partitioncount bigint; DECLARE @schemaname nvarchar(258); DECLARE @objectname nvarchar(258); DECLARE @indexname nvarchar(258); DECLARE @partitionnum bigint; DECLARE @partitions bigint; DECLARE @frag float; DECLARE @command varchar(8000); — ensure the temporary table does not exist IF EXISTS (SELECT name FROM sys.objects WHERE name = ‘work’) DROP TABLE work; — conditionally select from the function, converting object and index IDs — to names. SELECT object_id AS objectid, index_id AS indexid, partition_number AS partitionnum, avg_fragmentation_in_percent AS frag INTO work FROM sys.dm_db_index_physical_stats (DB_ID(), NULL, NULL , NULL, ‘LIMITED’) WHERE avg_fragmentation_in_percent > 10.0 AND index_id > 0; — Declare the cursor for the list of partitions to be processed. DECLARE partitions CURSOR FOR SELECT * FROM work; — Open the cursor. OPEN partitions; — Loop through the partitions. FETCH NEXT FROM partitions INTO @objectid, @indexid, @partitionnum, @frag; WHILE @@FETCH_STATUS = 0 BEGIN; SELECT @objectname = QUOTENAME(o.name), @schemaname = QUOTENAME(s.name) FROM sys.objects AS o JOIN sys.schemas as s ON s.schema_id = o.schema_id WHERE o.object_id = @objectid; SELECT @indexname = QUOTENAME(name) FROM sys.indexes WHERE object_id = @objectid AND index_id = @indexid; SELECT @partitioncount = count (*) FROM sys.partitions WHERE object_id = @objectid AND index_id = @indexid; — 30 is the decision point at which to switch — between […]
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Code for reindexing all tables in a database using dbreindex
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The following DMV query retrieves the usage statistics for existing indexes. User Seeks – A high number indicates a well utilized index. User Scans – Number of times the index has been scanned. Could indicate improper ordering of the composite columns User Lookups – Indicates a different index was used for criteria and the actual data was looked up from this index for the select list User Updates – Number of times the index was updated with additional records [cc lang=”sql”] SELECT ObjectName = object_schema_name(idx.object_id) + ‘.’ + object_name(idx.object_id) ,IndexName = idx.name ,IndexType = CASE WHEN is_unique = 1 THEN ‘UNIQUE ‘ ELSE ” END + idx.type_desc ,User_Seeks = us.user_seeks ,User_Scans = us.user_scans ,User_Lookups = us.user_lookups ,User_Updates = us.user_updates FROM sys.indexes idx LEFT JOIN sys.dm_db_index_usage_stats us ON idx.object_id = us.object_id AND idx.index_id = us.index_id AND us.database_id = db_id() WHERE object_schema_name(idx.object_id) != ‘sys’ ORDER BY us.user_seeks + us.user_scans + us.user_lookups DESC [/cc]
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One of the most common database performance issue most companies face is the improper choice of indexes or the lack of indexes. Most essential, is the clustered index. A well-chosen clustered index will save CPU, Memory, and IO. Choosing the clustered index for a table goes hand-in-hand with the writing of the queries for a table. It is best to design the queries and the index simultaneously to keep consistency. The majority of the time this is not an option. When we have not written the queries, the best way to understand the optimal clustered index is to study the queries that are run against the table. Once you understand the queries that run against a table, it is helpful to think of each of these queries broken down into three parts: The select list – Be on the lookout for the queries that return the most columns from the table. The join columns – The most common columns used to join other tables against the table. The where clause – The most common columns used to filter the result sets. Avoiding Fragmentation Before going into depth in choosing a clustered index we need to know what causes fragmentation. We ideally want to answer no to the following: Will the clustered value(s) be updated? Can new rows be inserted between already inserted clustered rows? The reason for answering no above is because we do not want fragmentation at the clustered level. The clustered index is like the foundation of a […]
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