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How to fix Slow running queries on SQL Server

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As a DBA, we carry out all the fundamental checks, including examining CPU and memory consumption, any blockings, deadlocks, locks, fragmentation, statistics updating, and so forth, when a user approaches you and complains that his query is taking too long to finish. After completing all of these checks, if the user is still experiencing slowness, we must carry out the procedures listed below to diagnose or resolve SQL Server queries that are running slowly.

Identify the slow-running queries: Find the slow-running queries by using SQL Server Management Studio (SSMS), which allows you to see the queries that are presently running and their current execution times. The SQL Server Profiler can be used to track down queries that are running more slowly than intended. You may use the profiler to filter and sort the traces depending on several factors including duration, CPU usage, reads, and writes.

Analyze the query execution plan: After you’ve found the slow-running query, you can utilize the execution plan to learn more about how it’s being processed. The execution plan displays the steps that SQL Server takes to carry out the query, together with the operations’ projected prices and their respective orders. You can find out if there are any possible indexing, join, or other query-related performance problems by looking at the execution plan.

Check for missing or outdated statistics: The query optimizer needs up-to-date information about the data distribution in the tables utilized in the query in order to produce effective execution plans. The optimizer might make less-than-optimal decisions and the query might execute more slowly than anticipated if the statistics are incomplete or out of date. To update the statistics, use either the UPDATE STATISTICS statement or the sp updatestats stored procedure.

Check for blocking: When one query has a lock on a resource that another query needs to access, blocking occurs. Performance may be slowed as a result of the second query having to wait until the lock is released. To check for any potential blocking, utilize the exec requests dynamic management view.

Check for resource contention: If the query is running slowly, use Performance Monitor to look for resource contention, such as high CPU or memory utilization. The resources that are leading to the highest waits can also be identified using the dynamic management view os wait stats.

Check for hardware issues: Look for any hardware problems that might be slowing down the query, including disc constraints or high network latency. To evaluate disc performance and locate any bottlenecks, utilize tools like Perfmon, SQLIOSim, and SQLIO. 

Optimize the query: Once the source of the poor performance has been found, you can improve the query by altering the query, the indexing, or other database infrastructure components. Adding or changing indexes, rewriting the query to employ more effective join methods, and using stored procedures rather than ad-hoc queries are all examples of common optimization strategies.

Monitor Performance: You may find and fix slow-running queries before they become serious issues by routinely monitoring the performance of your SQL Server instances, including query performance. You may track the performance of your SQL Server instances and fix any issues using the built-in performance monitoring tools in SQL Server, including SQL Server Management Studio (SSMS), SQL Server Profiler, and dynamic management views (DMVs).

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