Re: Overwhelming a Web Application Server

[Thorbjoern Ravn Andersen <ravn@xxxxxxxxxx>]

Nathan Andelin skrev:
> > From: Bradley V. Stone
> > But again I'd guess in most cases that ID is stored in DB file(s) and
> > looked up on each request, not in memory.
> >     
>
>
> I bet a lot of RPG-CGI programs use DB files to store session data, but I get the impression that Java objects are "serialized" to stream files, and typically larger - a developer may dump an SQL result set to a "collection" and store it in a "session", for example.  Maybe it depends on the application.
>   
Serialization in Java means that you flatten an arbitrary memory 
structure into a byte sequence (which can then be further manipulated 
like stored in a file or in a database table) after which the memory 
structure is often removed.   It can then be reconstructed by 
deserializing the byte stream, resulting in a new memory structure equal 
to the old one (if all goes well).

The usual reason for developers saving whole database results in memory 
is to my knowledge that you need carefully crafted database specific SQL 
to retreive results page by page.  This has become much easier with e.g. 
Hibernate and JPA which explicitly allow paging results and hide the 
database specific issues. 

If you can store session data in a database you automatically take a 
performance hit as you need to restore the session data from the 
database for every request.   This WILL take time and limit the amount 
of requests you can handle pr second.    I'd like to hear actual numbers 
from what this takes on the AS/400, as database access can be very 
expensive on other platforms.