Re: CGI vs JSP...

[Mel Rothman <mel@xxxxxxxxxxxxxx>]

CGIDEV2 "kind of" compiles the template and does not have to search the template itself 
at substitution time.

When used properly (more below), CGIDEV2 variable substitution performance just isn't an 
issue.

When CGIDEV2 reads a template record, it stores it in a memory-resident stream and places 
its offset into a memory resident array of offsets.

If the record contains any substitution variables, it makes an entry for each into a set 
of memory resident arrays that contain the substitution variable's RRN, starting position 
in its record, the substitution string, the length of the substitution string, and the 
section name.

When a section is written, CGIDEV2 uses the HTML records' offsets to extract each HTML 
record from the memory resident stream and %lookup with the record's RRN (%lookup uses 
binary search, so it's fast) to ascertain whether it has any substitution variables. If 
so, the entries in the arrays are used to perform variable substitution.  It was designed 
to be and is very efficient.

The part that involves a lot of work is processing the template into the stream and the 
arrays.

However, that processing does not have to be performed every time the CGI program runs 
because the 2nd and subsequent runs in the same activation group reuse the data previously 
stored in the stream and the arrays.

I always recommend that frequently used CGIDEV2 programs be created with named activation 
groups. In such programs, once template processing has been done, it is not done again 
until  the list of template files changes or any of them is modified (date/timestamp 
changes).  Usually, this is not during the activation group's lifetime.

If multiple programs use the same activation group, each of them should use the same list 
of template files to ensure that the templates are not processed again and again. 
Alternatively, each program could have its own activation group name.

The things that most slow down CGIDEV2 are not using named activation groups and leaving 
debugging on after it is no longer needed.


Mel Rothman
CGIDEV2 Author




Seth Newton wrote:
> Brad, 
>
> In a CGIDEV2 application, there is an HTML template that uses replacement
> variables where your dynamic content will go. At runtime, APIs are used to
> search/replace the replacement variables with their appropriate values.  The
> difference in performance is quite noticeable, especially with a subfile
> application that loads many records. 
>
> RPGsp’s compile process pre-determines which variables and expressions will
> be need to be output to the browser at compile-time. When the application
> runs, sections of HTML are output as needed, and the value of variables or
> expressions are also output directly, with no search/replace taking place.
>
> As an example, let's say this is our template:
>
> Item Number: <%ITEM%> <br>
> Item Description: <%DESC%>
>
> With CGIDEV2 and other similar tools, the logic flows like this:
>
> 1. Read Template.
> 2. Search my template for <%ITEM%> and replace it with RPG variable ITEM.
> 3. Search my template for <%DESC%> and replace it with RPG variable DESC.
> 4. Output template.
>
> Steps 2 and 3 are CPU-intensive.  In a subfile application, these Search
> steps may be repeated thousands of times.
>
> RPGsp, on the other hand, reads the template at compile time, and
> restructures it to execute like this. 
>
> 1. Output "Item Number:"
> 2. Output the value of RPG variable ITEM 
> 3. Output "<br> Item Description:"
> 4. Output the value of RPG variable DESC
>
> Here, we have no CPU-intensive search/replace logic, which results in much
> faster code.   
>
> Seth Newton
> snewton@xxxxxxxxxxxxxxxxx
> Profound Logic Software, Inc.
> Toll-Free: (877) 224-7768 x115
> Fax: (603) 849-7757
>
> RPGsp - iSeries Web Development has never been this easy!
> Watch video demos: http://www.profoundlogic.com/video_demos/
>
>
>
> -----Original Message-----
>
> > I am used to working with CGI from RPGsp (www.RPGsp.com), which allows 
> > you to embed RPG variables into HTML templates.  However, the 
> > templates are not searched at runtime.  The pages are compiled in a 
> > similar way JSP's are created, and that's why it's fast ... most 
> > likely faster than equivalent JSP's.
>
> Explain how this works.  how can data from a DB be replaced anywhere except
> for runtime.  
>
> Any time you're building dynamic applications data HAS to be
> inserted/replaced/built at runtime.
>
> Brad