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Explain Table Scan and Index Scan.- We use queries to improve the performance.
- SQL Server has to process more data to find the records that meet the queries criteria because of one common problem that exists is the lack of indexes or incorrect indexes .
- These issues are known as Index Scans and Table Scans.
- When SQL Server has to scan the data or index pages to find the appropriate records it is known as an index scan or table scan .
- A seek uses the index to pinpoint the records that are needed to satisfy the query and a scan is totally opposite of a seek.
- We need to find and fix scans as they generally require more I/O and also take longer to process.
- At its first release the performance is great, but as time passes and as more data is added the index scans take longer and longer to complete.
- These issues can be found by running Profiler or setting up a server side trace and look for statements that have high read values.
- Once the statements are identified then they can be seen at the query plan to see if there are scans occurring.
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