drupal 7 on virtual server with debian linux - inconsistent response time I have drupal 7 test installation on shared hosting. Caching turned off (I do not want to use caching), cron disabled. According to devel, query execution times on page with 228 queries are approximately 1200ms.(some views blocks with relationships, page displayed using context) Loading time of this page is allways more than 1200ms. It is approximately 3 and more seconds. Due to time to first byte, which I am not able to cut down.  
However, I decided to try the same install on virtual host running on debian linux 500mb ram. Devel shows on the same page (228 queries) time 50ms - which is great. 
But, accessing time to pages is very inconsistent. Sometimes it is amazingly fast, sometimes it takes 8 seconds of waiting and then page loads. What is interesting - even if page loads after 8 seconds, the query time is allways small according to devel.  This leads me to conclusion, that there must be some bad setting on my linux installation. Can anybody point me to the right direction? Thank you

I am new to virtual servers and I think I am missing here something obvious.
500 MB is not much, unfortunately :)
and the default debian settings for Apache and MySQL are prepared for bigger servers. You should make sure the server doesnt swap.

Probably the most important setting for that is in the part mpm_prefork_module in the apache configuration (/etc/apache2/apache2.conf). You will want to have less Startservers, MinSpareServers and MaxSpareservers.

Installing APC helps, too (and is relatively easy). Even though you have to sacrifice some RAM, it speeds up the loading and reduces the RAM needed for every pageload. With 500MB, you will want to use APC only as opcode. Make sure you dont use much more stuff than 1 installation of drupal, or set APC so that other stuff doesnt get cached (the default settings caches every php file you use, thus probably pushing the important stuff away).

Enable the css + js aggregation - apart from saving roundtrips for the client, it also saves your server from serving extra files.

Also take into account that drupal does some caching internally and the times when it takes longer may be because of that - it is useful to "prime" the caches ie by crawling all pages before you start measuring.

2bits have great articles about optimizing for drupal.