I have my own website that displays some data I get from webscraping.  I run the webscraping script on my website host server.  I just realized that maybe I'm accessing other websites too quickly through this script. For example, I just wrote a script that accessed 15 websites on the same domain in about a second.  My own website server crashed shortly thereafter.  My webhost was having some other problems so I don't know if these two events are related or not.But, I guess it brought up another question.  Do I need to limit how fast I access websites to prevent a denial of service (DOS) type warning from either the website I'm accessing or my own webserver host?  Is there some sort of safe rate of websites per second or per minute I should follow?  Just wondering,EDIT: To clarify, yes I could slow down the collection process but I'm actually scraping a lot of small pieces of information from different sites so accessing a lot of websites might be unavoidable.  Also, based on what I'm doing, getting the information as quickly as possible would be beneficial.  So I can slow the process down but I guess I'm looking for how much I can push the limit to get the information in the optimal time.        
Is there a limit to how often I should access a website programically to avoid DDOS?
web development;websites;web scraping;web hosting
There is no well defined limits, but by looking into the access log of my http://gcc-melt.org/ site (which is quite specialized and has only about a thousand hits per day, including robots), I see that well behaved bots:are querying the robots.txt file and following itare making requests spaced by a few seconds (typically 5) at least I would advise your program to behave likewise. Don't query the same website more than once every few seconds (in a rate similar to what humans are browsing). Of course your webscraper can make requests to other sites before that.If you are querying (programmatically) some particular website very often (e.g. more than once per second), I would suggest to at least try to contact (by email) its human webmaster. Some webmasters are blocking requests from hosts which query them too often.Remember that some web sites (like mines) are paid by individuals, and their hosting contract may put some limits (typically on bandwidth or monthly data volume). So you should be nice with them.