Selects are slow when blob field?

[nmongeau]

Hi,

I have a table with this structure

* tablename varchar(100)
* recordid unsigned int(10)
* tag varchar(100)
* sequence unsigned smallint(5)
dataholder mediumblob
datalength unsigned int(10)

fields with an asterisk are indexed, and the mediumblob field holds 8000000 bytes for each record. The table presently contains 85 records, but a simple select like this:

select datalength from datastore where tablename='Clipboard' and recordid=15;

returns 28 rows and takes a staggering 16.05 seconds. Running the same query immediately after takes 0.5 seconds. But changing an argument to the query makes it go back to roughly 15 seconds.

Is there anything wrong with this setup, and why are the queries taking sooooo long? BTW it's version 4.0.16, running on an WinXP box.

Thanks,

Normand