What can cause bad SQL server performance?

Question

Every time I find out that the performance of data retrieval from my database is slow. I try to figure out which part of my SQL query has the problem and I try to optimize it and also add some indexes to the table. But this does not always solve the problem.

My question is :

Are there any other tricks to make SQL server performance better?

What are the other reason which can make SQL server performance worse?

Answer 1

• Inefficient query design
• Auto-growing files
• Too many indexes to be maintained on a table
• Too few indexes on a table
• Not properly choosing your clustered index
• Index fragmentation due to poor maintenance
• Heap fragmentation due to no clustered index
• Too high FILLFACTORs used on indexes, causing excessive page splitting
• Too low of a FILLFACTOR used on indexes, causing excessive space usage and increased scanning time
• Not using covered indexes where appropriate
• Non-selective indexes being used
• Improper maintenance of statistics (out of date statistics)
• Databases not normalized properly
• Transaction logs and data sharing the same drive spindles
• The wrong memory configuration
• Too little memory
• Too little CPU
• Slow hard drives
• Failing hard drives or other hardware
• A 3D screensaver on your database server chewing up your CPU
• Sharing the database server with other processes which compete for CPU and memory
• Lock contention between queries
• Queries which scan entire large tables
• Front end code which searches data in an inefficent manner (nested loops, row by row)
• CURSORS which are not necessary and/or are not FAST_FORWARD
• Not setting NOCOUNT when you have large tables being cursored through.
• Using a transaction isolation level which is too high (such as using SERIALIZABLE when it's not necessary)
• Too many round trips between the client and the SQL Server (a chatty interface)
• An unnecessary linked server query
• A linked server query which targets a table on a remote server with no primary or candidate key defined
• Selecting too much data
• Excessive query recompilations

oh and there might be some others, too.