# Horribly Slow RJS/Ajax Rendering Compared to Non? **URL:** \ **Category:** Rails\ **Created:** [November 25, 2006, 6:39am UTC](https://www.ruby-forum.com/t/horribly-slow-rjs-ajax-rendering-compared-to-non/77217 "2006-11-25T06:39:36Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![slain](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/2acd7d/32.png) [@slain](https://www.ruby-forum.com/u/slain)\ **Post date:** [November 25, 2006, 6:39am UTC](https://www.ruby-forum.com/t/horribly-slow-rjs-ajax-rendering-compared-to-non/77217/1 "2006-11-25T06:39:36Z")
Hi, I’m seeing some pretty bad numbers when doing Ajax updates in the Rails logs, compared to rendering the same thing without ajax. On a complete browser refresh, which is using render\_component, I am seeing the main content of my application render at 42 req/s, 22 req/s overall when including the layout outside of the rendered component. When I click a link that renders the same exact content as the render\_component does, I get 5-8 req/s. This is 5 times slower… just to wrap it up in a Element.update. Is the Ajax/RJS implementation that bad? Or am I missing something? Is it javascript escaping in some horribly inefficient way? Ie. ajax was supposed to make things go faster, lol, not 5 times slower. The page does load faster overall, but why is the performance sooo bad? ---
**Author:** ![slain](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/2acd7d/32.png) [@slain](https://www.ruby-forum.com/u/slain)\ **Post date:** [November 25, 2006, 10:42am UTC](https://www.ruby-forum.com/t/horribly-slow-rjs-ajax-rendering-compared-to-non/77217/2 "2006-11-25T10:42:26Z")
There are cases in which rjs is not optimal. If your ajax call generates a large amount of rhtml then that rhtml has to be escaped so that it fits into a javascript string, and then on the browser side, the client has to parse that large chunk of javascript and execute it. So if your rjs is just page.replace\_html foo or page.insert\_html foo then you are often better off using the :update option of link\_to\_remote and friends. Fred ---
**Author:** ![slain](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/2acd7d/32.png) [@slain](https://www.ruby-forum.com/u/slain)\ **Post date:** [November 25, 2006, 12:30pm UTC](https://www.ruby-forum.com/t/horribly-slow-rjs-ajax-rendering-compared-to-non/77217/3 "2006-11-25T12:30:38Z")
That’s a big slowdown for a reasonably small amount of js. I had nothing like that much of a slow down with a rather big page load. Have you tried using action\_profiler ([http://rails-analyzer.rubyforge.org/action\_profiler/](http://rails-analyzer.rubyforge.org/action_profiler/)) to see exactly where the time is going? ---
**Author:** ![slain](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/2acd7d/32.png) [@slain](https://www.ruby-forum.com/u/slain)\ **Post date:** [November 26, 2006, 3:28am UTC](https://www.ruby-forum.com/t/horribly-slow-rjs-ajax-rendering-compared-to-non/77217/4 "2006-11-26T03:28:43Z")
Fred wrote: > That’s a big slowdown for a reasonably small amount of js. I had > nothing like that much of a slow down with a rather big page load. > Have you tried using action\_profiler > ([http://rails-analyzer.rubyforge.org/action\_profiler/](http://rails-analyzer.rubyforge.org/action_profiler/)) to see exactly > where the time is going? I haven’t played around with action\_profiler since I made the to\_json patch. The main problem with action\_profiler is that it having it tell me it spend 10% of its time in Kernel#=== isn’t as helpful as it could be :P. I’ve installed the eval version of Ruby Performance Validator, which supposedly has call graphs, but I have no idea how to run it on a Rails app, and there’s no docs that I have been able to find on doing so, and no response from a support email I sent them. Performance is much closer to what I would expect, with the to\_json patch, it’s just so hard to tell, cause half the time the a request goes thru at 32 req/sec the other times at 12…with no real obvious reason for it, besides some really bad garbage collection. ---
**Author:** ![slain](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/2acd7d/32.png) [@slain](https://www.ruby-forum.com/u/slain)\ **Post date:** [November 25, 2006, 11:31am UTC](https://www.ruby-forum.com/t/horribly-slow-rjs-ajax-rendering-compared-to-non/77217/5 "2006-11-25T11:31:05Z")
Fred wrote: > There are cases in which rjs is not optimal. > If your ajax call generates a large amount of rhtml then that rhtml has > to be escaped so that it fits into a javascript string, and then on the > browser side, the client has to parse that large chunk of javascript and > execute it. > So if your rjs is just page.replace\_html foo or page.insert\_html foo > then you are often better off using the :update option of link\_to\_remote > and friends. > > Fred Yes it appears escaping is the culprit. Adding the to\_json patch from [http://dev.rubyonrails.org/ticket/3473](http://dev.rubyonrails.org/ticket/3473) seems to help considerably, though escape\_javascript in 1.1.6 doesn’t use to\_json it, so must be getting used somewhere else. And performance could be better even still. I’m not really concerned with browser side performance. We are talking 5K worth of data, is that ‘large amount’? So, I’m guessing that link\_to\_remote :update doesn’t need to have anything escaped would be the difference… unfortunately, that sort of limits my options. Ie. If someone tries to adjust a slider when they arent logged in, I want to update a flash div, as well as redraw the sliders back to their unmoved state, for example. Are the internals of gsub able to handle this stuff efficiently? Ie., are too many reallocation/copies happening because of the number of extra chars that are being added to escape the various punctuation and whitespace? Are there ways to have it preallocate enough space (2x the string size would be the obvious choice, in the worst case scenario of all escaped chars.) And this really kind of screws with fragment caching too, since if 80% of the cost of a method is escaping the javascript lol…I don’t care how you do it, 500% increase in rendering time due to escaping is pretty bad. Thanks.