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| | From Microsoft ”
The SQL Server Database Engine automatically maintains indexes whenever insert, update, or delete operations are made to the underlying data. Over time these modifications can cause the information in the index to become scattered in the database (fragmented).
Fragmentation exists when indexes have pages in which the logical ordering, based on the key value, does not match the physical ordering inside the data file. Heavily fragmented indexes can degrade query performance and cause your application to respond slowly.
You can remedy index fragmentation by either reorganizing an index or by rebuilding an index. For partitioned indexes built on a partition scheme, you can use either of these methods on a complete index or on a single partition of an index. |
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| | Costly missing indexes:
Indexes are typically the most important factor in identifying the relevant data rows quickly. As much as an index has a big impact on quickly identifying rows of data, a missing index can have a corresponding detrimental impact on performance. When SQL Server runs queries, it examines the query and tables/views and determines which indexes it would like to use. If these indexes are present, it typically uses them.
Finding the most important missing indexes Indexes are a principal means of improving the performance of SQL queries. For various reasons, for example, changing systems, useful indexes may not always have been created.
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| | Resource Bottlenecks
CPU, memory, and I/O subsystem resources and can become bottlenecks. For each resource bottleneck, you can identify the problem and then iterate through the possible causes. For example, a memory bottleneck can lead to excessive paging, which can ultimately impact performance.
Before you can determine if you have a resource bottleneck, you need to know how resources are used under normal circumstances. You can collect baseline information about the use of the resource (when you are not having performance problems).
You might find that the problem is a resource that is running near capacity and that SQL Server cannot support the workload in its current configuration. To address this issue, you may need to add more processing power, memory, or increase the bandwidth of your I/O or network channel. But, before you take that step, it is useful to understand some common causes of resource bottlenecks.
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Memory Pressure
Large Queries, Updates, Cached Plans and other server items can cause pressure on MSSQL to manage memory and reduce the performance of your DB, inefficient statements, waits can also contribute.
It is not uncommon to experience the occasional slow down of a SQL Server database. A poorly designed database or a system that is improperly configured for the workload are but several of many possible causes of this type of performance problem.
Many can experience an occasional slow down of their SQL Server database. The reasons can range from a poorly designed database to a system that is improperly configured for the workload.
As an administrator, you want to proactively prevent or minimize problems and, when they occur, diagnose the cause and, when possible, take corrective actions to fix the problem.
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