clustered-index | 易学教程

INSERTs with sequential GUID key on clustered index not significantly faster

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问题 In SQL Server 2008 I have tried to reproduce the results from the experiments on clustered index on sequential vs. non-sequential GUID keys seen here http://sqlblog.com/blogs/denis_gobo/archive/2009/02/05/11743.aspx but I do not experience the significant speedup for insertions that I would expect (and the author experiences). The page utilization is clearly improved with the sequential GUID, but for some reasons, inserting 10,000 rows is only around 100 ms faster (out of 10,300 ms). I use

Should primary keys be always assigned as clustered index

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问题 I have a SQLServer table that stores employee details, the column ID is of GUID type while the column EmployeeNumber of INT type. Most of the time I will be dealing with EmployeeNumber while doing joins and select criteria's. My question is, whether is it sensible to assign PrimaryKey to ID column while ClusteredIndex to EmployeeNumber? 回答1: The ideal clustered index key is: Sequential Selective (no dupes, unique for each record) Narrow Used in Queries In general it is a very bad idea to use

indexes in sql server, internal working and structure of indexes

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问题 when we create a clustered index CIX_FirstNames on a column , say, FirstNames , then what actually happens internally in SQL Server? i have read that clustered indexes create copy of the data. so, does sql server creates a new index table, IndexTable , and copies all the FirstNames from the table into IndexTable , and when a firstname is searched, then it displays it from the index table? is this the actual working of clustered indexes ? 回答1: This is way too big a topic to handle here in a

SQL Azure not recognizing my clustered Index

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问题 I get the following error when I try to insert a row into a SQL Azure table. Tables without a clustered index are not supported in this version of SQL Server. Please create a clustered index and try again. My problem is I do have a clustered index on that table. I used SQL Azure MW to generate the Azure SQL Script. Here's what I'm using: IF EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[tblPasswordReset]') AND type in (N'U')) DROP TABLE [dbo].[tblPasswordReset] GO SET

Optimizing queries based on clustered and non-clustered indexes in SQL?

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问题 I have been reading lately about how clustered index and non-clustered index works. My understanding in simple terms (correct me if wrong): The data structure that backs clustered and non-clustered index is B-Tree Clustered Index : physically sorts the data based on the index column (or key). you can have only one clustered Index per table . If no index is specified during table creation, SQL server will automatically create a clustered Index on the primary key column . Q1 : Since data is

SQL Server database with clustered GUID PKs - switch clustered index or switch to sequential (comb) GUIDs?

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问题 We have a database in which all the PKs are GUIDs, and most of the PKs are also the clustered index for the table. We know that this is bad (due to the random nature of GUIDs). So, it seems there are basically two options here (short of throwing out GUIDs as PKs altogether, which we cannot do (at least not at this time)). We could change the GUID generation algorithm to e.g. the one that NHibernate uses, as detailed in this post, or we could, for the tables that are under the heaviest use,

SQL Azure not recognizing my clustered Index

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I get the following error when I try to insert a row into a SQL Azure table. Tables without a clustered index are not supported in this version of SQL Server. Please create a clustered index and try again. My problem is I do have a clustered index on that table. I used SQL Azure MW to generate the Azure SQL Script. Here's what I'm using: IF EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[tblPasswordReset]') AND type in (N'U')) DROP TABLE [dbo].[tblPasswordReset] GO SET ANSI_NULLS ON SET QUOTED_IDENTIFIER ON IF NOT EXISTS (SELECT * FROM sys.objects WHERE object_id =

Clustered index on temp table

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I'm trying to optimize a procedure that has code like the following: CREATE TABLE #t1 (c1 int, c2 varchar(20), c3(varchar(50)...) CREATE CLUSTERED INDEX ix_t1 ON #t1(c3) ON [PRIMARY] I wanted to improve that by moving the CLUSTERED index into the table declaration (more caching friendly), but c3 is not unique so this doesn't work: CREATE TABLE #t1 (c1 int, c2 varchar(20), c3 varchar(50)..., UNIQUE CLUSTERED (c3)) Is there a way to declare a clustered that is not unique in the temp table declaration? No there is not...the existence of the ability to define clustered as an option in table

B-trees, databases, sequential vs. random inserts, and speed. Random is winning

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EDIT @Remus corrected my test pattern. You can see the corrected version on his answer below. I took the suggestion of replacing the INT with DECIMAL(29,0) and the results were: Decimal: 2133 GUID: 1836 Random inserts are still winning, even with a fractionally bigger row. Despite explanations that indicate random inserts are slower than sequential ones, these benchmarks show they are apparently faster. The explanations I'm getting aren't agreeing with the benchmarks. Therefore, my question remains focused on b-trees, sequential inserts, and speed. ... I know from experience that b-trees have

Optimizing queries based on clustered and non-clustered indexes in SQL?

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I have been reading lately about how clustered index and non-clustered index works. My understanding in simple terms (correct me if wrong): The data structure that backs clustered and non-clustered index is B-Tree Clustered Index : physically sorts the data based on the index column (or key). you can have only one clustered Index per table . If no index is specified during table creation, SQL server will automatically create a clustered Index on the primary key column . Q1 : Since data is physically sorted based on index, there is no extra space needed here. is this correct? so what happens