A general recommendation for all SQL tables is to have a proper clustered index The data in the clustered table is sorted using the values of the columns the clustered index is made of.įinding a record from a table with a proper clustered index is quick and easy like finding a name in an alphabetically ordered list.
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a pointer to the data row that contains the key value, but it also contains table data.
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In other words, it is not just an index, i.e. A clustered index consists of both index and data pages, while a heap table has no index pages it consists only of data pages. It doesn’t contain data pages, like clustered indexes.Ī clustered index organizes table data, so data is queried quicker and more efficiently. It is inefficient and requires time.Ī heap can have one or several nonclustered indexes, or no indexes at all.Ī nonclustered index is made only of index pages that contain row locators (pointers) for records in data pages. Finding a record in a heap table can be compared to finding a specific leaf in a heap of leaves. When you insert a lot of rows into a heap table, the new records are written on data pages without a specific order. They can also be rearranged by the database engine, but again, without a specific order. Data in a heap table isn’t sorted, usually the records are added one after another, as they are inserted into the table. We will start with explaining clustered and nonclustered indexes.Ī table without a clustered index is called a heap, due to its unordered structure. The biggest challenge with indexing is to determine the right ones for each table. The database indexes reduce the number of data pages that have to be read in order to find the specific record. What are indexes?Īn index is used to speed up data search and SQL query performance. Poor indexing is one of the top performance killers, and we will focus on them in this article.
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With these factors present on your machine, even adding additional hardware resources might not help, as these SQL Server performance killers can use all available resources. The most common SQL Server performance killers are poor database design, poor indexing, poor query design, not reusable execution plans, frequent query recompilation, excessive fragmentation, and more. SQL Server performance is affected by many factors.