Huge delay on first request due to many slow SQL queries Possible Duplicate:
  Performance Problem: Delay on first request  




The first page of my site takes up to 15 secs to load and then the site become responsive. If I leave the site for 20 min or so, the first request is very long again. 

Following recommendations found on this similar question, I checked the Devel query logs and there is a whole bunch of queries related to field_sql_storage_field_storage_load taking more than 250ms. 
I am not sure it is purely related to field_sql_storage_field_storage_load though as there is another language_list query with a simple SELECT * FROM languages ORDER BY weight ASC, name ASC taking 186ms. 

My questions are: why do I encounter such delays and how can I reduce them?
So this is how I fixed the problem. It is not a real solution as I could not nail the exact source of the problem (if there is one).

1) Aggregate CSS (cache settings). This reduced the latency by half
2) Set cron to never (and run it externally)
3) Set up a cron job that calls the home page with Lynx every 30 minutes