[stringtemplate-interest] huge memory improvement for sites using ST

[Terence Parr]

Hi, my former business partner, Tom Burns, is building  
www.schoolloop.com and just discovered that having ST write straight  
to the output stream is much better than writing to a string and then  
writing out.  He says:

> http://schoolloop.com gets about 1 million page views a day.  We were
> having some performance issues, so I was looking around for some
> "big win" improvements.  I definitely found one.
>
> SchoolLoop uses StringTemplate for all of its page generation.  I made
> a simple change to the core method --  generatePage -- and the sites
> behavior at peak times changed drastically.  We went from having about
> 300M out of 3G free to having about 2G out of 3G free.  Obviously,  
> this is
> just one sample, but it gives you a good idea of the change in  
> behavior we
> have observed.  The time between full garbage collections went from  
> about
> 20 minutes to about 5 or 6 hours.
>
> All I did was change this:
>
>     public void generatePage(PrintWriter pageOut) throws Exception
>     {
>         StringTemplate page = generatePage();
>         pageOut.write(page.toString());
>     }
>
>
> to this:
>
>     public void generatePage(PrintWriter pageOut) throws Exception
>     {
>         StringTemplate page = generatePage();
>         NoIndentWriter writer = new NoIndentWriter(pageOut);
>         page.write(writer);
>     }
>
> The problem with toString() is that it uses a StringBuffer to store
> the intermediate strings -- and it has no idea how big the buffer
> will ultimately be.  So it makes very bad guesses in the worst case  
> (on
> schoolloop, some pages are over 500k) and it has to iteratively  
> allocate
> new, larger buffers and copy the existing buffer to the new one.
>
> Thomas E. Burns
> Co-Founder/CTO, Schoolloop.com