Hello i'm tweaking a server with magento store and i've a thouble with the "first byte time". Magento store take 6 secs to start downloading page. How i can make it faster?
I've already config varnish, apc and cdn cloudflare.
Which page are you talking about? Homepage, Category, Detail page etc...? 6 seconds for your TTB is very high
If it was me - I would (on a dev site) - disable all plugins and your theme - test the speed again - hopefully its better... then layer each plugin back on one by one; and test after each enable (clearing cache inbetween) - making a note of any speed differences.
Once all your modules are back on - finally re-enable your theme. Once again - test for speed again.
This should help you diagnoise where the problem is occuring.
Is this a new Magento store or has it been running for some time?
To quote what I have stated in another topic:-
1. Are you using any extensions that can slow things down (this is very normal and happens all the time)? Use the Magento profiler to identify any problematic extensions.
2. Are your Magento logs regularly cleaned? Make sure that Log Cleaning is enabled (and the Cron Job is running) as the logs can make your database bloated which will slow things down.
3. Are all application level optimizations already performed? Things like enabling Magento cache, GZip compression, etc.
4. As for the server or hosting level, is the server properly optimized for Magento? Is the MySQL properly tweaked to match your store?
try runing the site through GT Metirx (https://gtmetrix.com/) or something similar. It won't fix all your issues, but might flag some things that could be improved.
We had speed issues with our Store as it was quite image heavy.Our issue was the virtual server couldn't hack it as it had shared resources.
We've moved to a dedicated server and the difference in speed is massive.
@river11: Yes, it is also possible that the server you were on is not powerful enough but that should be very easy to identify (hitting the CPU limit, exhausting the Memory, etc) and upgrading or adding more resources like CPU and Memory should do the job.