Delay on each 'Select' request

[SARTrack]

I have an application which received up to 10 data packets per second, each of which must be either Interted or Updated in one or more Tables.
The big problem is, that each of my Select statements (which I need to retrieve the existing record, before I can Update it), takes always at least 45 miliseconds on my 4-core PC.
This is regardless if there is any data returned, or if the SQL Database table is completely empty of has 1000 records in it.

I run MySQL 5.1, and my program on the same PC.
Loadlevels are low.

There is just that huge 45 milisecond delay on each Select. What is the cause of this? I cannot use the system with these huge delays.

Thanks, Bart

[AndreyZ]

Please specify the method (a code example) which you use to detect a delay in executing of SELECT statements.