What affects SQL performance?

Query performance also depends on data volume and transaction concurrency. Executing the same query on a table with millions of records requires more time that performing the same operation on the same table with only thousands of records. A lot of concurrent transactions can degrade SQL Server performance.

What is SQL logical reads?

A logical read occurs every time the Database Engine requests a page from the buffer cache. If the page is not currently in the buffer cache, a physical read first copies the page from disk into the cache. In other words, when SQL Server reads data from the memory, it is called Logical Read.

How reduce logical reads in SQL Server query?

Usually the best way to reduce logical read is to apply correct index or to rewrite the query. Physical read indicates total number of data pages that are read from disk. In case no data in data cache, the physical read will be equal to number of logical read. And usually it happens for first query request.

How wait types can effect the performance of SQL Server?

When a query encounters something that is not available, SQL Server sets wait type for that wait reason. This data is retained in SQL Dynamic Views which we can use to understand why things are slower than expected.

How increase SQL JOIN performance?

It’s vital you optimize your queries for minimum impact on database performance.

1. Define business requirements first.
2. SELECT fields instead of using SELECT *
3. Avoid SELECT DISTINCT.
4. Create joins with INNER JOIN (not WHERE)
5. Use WHERE instead of HAVING to define filters.
6. Use wildcards at the end of a phrase only.

How can I see logical reads in SQL Server?

Below are the ways to check logical Reads:

1. set statistics io on.
2. sys.dm_exec_query_Stats. by executing the below statement we can find detailed info about reads/writes. select * from sys.dm_exec_query_Stats.
3. SQL Profiler: by executing the sql profiler on that database we can find out logical reads..

What are SQL Server logical writes?

A logical write occurs when data is modified in a page in the buffer cache. A physical write occurs when the page is written from the buffer cache to disk. SQL Server uses a technique known as write-ahead logging that prevents writing a dirty page before the associated log record is written to disk.

How reduce scan count and logical reads in SQL Server?

You can reduce the scan count by proper indexing for Orders and Ordershistory. You may be able also to restructure the query to use JOINs instead.

What is wait stats in SQL Server?

What is SQL Server wait statistics? The wait times are captured and recorded by the SQL Server and all this captured information called wait statistics and it provides assistance to resolve problems that are related to the SQL Server performance.