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SQL Server caches the databases in what's called a buffer pool. A buffer pool acts as a storage space for data pages that have been recently written or read to and from disk. A small buffer pool will slow down your SQL application by overwhelming the disk's subsystem.
Queries can become slow for various reasons ranging from improper index usage to bugs in the storage engine itself. However, in most cases, queries become slow because developers or MySQL database administrators neglect to monitor them and keep an eye on their performance.
I have a sql query that runs super fast, around one second, when not using variables, like:
WHERE id BETWEEN 5461094 and 5461097
But when I have:
declare @firstId int
declare @lastId int
set @firstId = 5461094
set @lastId = 5461097
...
WHERE id BETWEEN @firstId and @lastId
... the query runs really slow, finishing only after some minutes. Why does it happen? I need to use variables. Can I do any improvement to avoid this performance problems?
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