Favourite performance tuning tricks [closed]

Answer 1

Slightly off topic but if you have control over these issues...
High level and High Impact.

• For high IO environments make sure your disks are for either RAID 10 or RAID 0+1 or some nested implementation of raid 1 and raid 0.
• Don't use drives less than 1500K.
• Make sure your disks are only used for your Database. IE no logging no OS.
• Turn off auto grow or similar feature. Let the database use all storage that is anticipated. Not necessarily what is currently being used.
• design your schema and indexes for the type queries.
• if it's a log type table (insert only) and must be in the DB don't index it.
• if your doing allot of reporting (complex selects with many joins) then you should look at creating a data warehouse with a star or snowflake schema.
• Don't be afraid of replicating data in exchange for performance!

Answer 2

@Terrapin there are a few other differences between isnull and coalesce that are worth mentioning (besides ANSI compliance, which is a big one for me).

Coalesce vs. IsNull

Answer 3

Index the table(s) by the clm(s) you filter by

Answer 4

Dirty reads -

set transaction isolation level read uncommitted

Prevents dead locks where transactional integrity isn't absolutely necessary (which is usually true)

Answer 5

First step: Look at the Query Execution Plan!
TableScan -> bad
NestedLoop -> meh warning
TableScan behind a NestedLoop -> DOOM!

SET STATISTICS IO ON
SET STATISTICS TIME ON