On 17/10/18 22:25, Stephen Smith wrote: > I have written a screen scraping program that watches a clock (on the app's > server) and at 7:00:00 AM dashes to make a reservation on line. It works > fine. However, i have spent time trying to improve its performance. I am > using selenium, with chrome driver.
When doing performance tuning the first thing to answer is what does improved performance mean. For example in a Word Processor improving the speed that an input character appears on screen by 10% is unlikely to be a worthwhile exercise. But improving the time taken to do a global search/replace by 10% might well be worthwhile. So what do you want to improve about an app that spends most of its time waiting for a change on a remote server (presumably by polling?) Is it the speed/frequency of polling? The speed of reading the response? The speed of processing the response? And knowing what you want to improve have you measured it to see where the time is being spent? Is it in the client request? The transmission to the server? the server processing? the transmission from the server? the reading of that response? or the processing of that response? You need to time each of those phases accurately to find out which bits are worth improving. > Here is what i have learned. I have tried various methods to find (by > link_text, by_xpath, etc.) and click on the element in question (shown > below). When i find the element with no click, the find process takes about > .02 seconds. When i find it with a click (i need to select the element and > move to the next iframe) it takes over a second. I get these same results no > matter which find_element_by variation i use and i get the same times in > headless or normal mode. > > Here is my theory - finding the element is relatively simple in the html > already loaded into my machine - hence .02 seconds. However, when i click on > the element, processing goes out to the server which does some stuff and i > get a new iframe displayed, all of which takes time. Absolutely. network access is likely to be measured in 10ths of a second rather than hundredths. And processing the request may well entail a server database call (which may itself be on a separate machine from the web server with a corresponding LAN message delay), then there's the creation and transmission of the HTML (unless your server provides an API with JSON responses - but then you don't need clicks etc!) And iFrames make that worse since every iframe effectively gets treated as a separate html document. Then when your client receives the data it has to reparse the html into a document structure before performing the search. > concluded that perhaps I can't take a big chunk of that time out You probably can, but only if you have access to the server code and the network infrastructure and deep enough pockets for a server upgrade or a new proxy server. Assuming that's not the case then no, you need to look at other options. But your first step has to be to measure the various stages of the request. If the problem lies in the transmission time across the network there is probably not much you can do. If its in the database access (trickier to measure if you don't have the server code - you need to create some simultaneous equations using multiple test scenarios) then you might be able to construct better queries (eg look at a different page or only query the target iframe). > considered something other than selenium, but since i think the problem lies > on the server side, not sure it is worth the time. It depends on the nature of the page. The best solution, by far, is not to do web scraping. Its always the worst case solution and to be avoided if at all possible. Try to find an API with JSON or XML responses. Also, are you sure you need to use the clock on the page? Isn't the server clock adequate? In which case the response time should be in every message header so there's no need for web scraping at all... Finally, I think there is an active Selenium discussion forum so you could try there for more ideas. -- Alan G Author of the Learn to Program web site http://www.alan-g.me.uk/ http://www.amazon.com/author/alan_gauld Follow my photo-blog on Flickr at: http://www.flickr.com/photos/alangauldphotos _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
