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Date: Tue, 10 Aug 2010 23:31:29 +0200
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To: Tomcat Users List <users@tomcat.apache.org>
Subject: Re: [OT] Tomcat unexpectedly shuts down
References: 
 <SNT128-W26D6415B44B8007DDEC591A2940@phx.gbl>,<99C8B2929B39C24493377AC7A121E21F99011AA516@USEA-EXCH8.na.uis.unisys.com>,<SNT128-W269905F5623D098C82C78FA2940@phx.gbl>,<99C8B2929B39C24493377AC7A121E21F99011AA6B5@USEA-EXCH8.na.uis.unisys.com>
 <SNT128-W62D6D2841A8765E1D69436A2940@phx.gbl> <4C607F1A.4030802@ice-sa.com>
 <4C618343.5030506@christopherschultz.net>
In-Reply-To: <4C618343.5030506@christopherschultz.net>
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Christopher,

I have no fundamental contest with anything you say below (except one, see in text).
It is just that 3000 MB is *a lot* of bytes (3,145,728,000 of them).
It is, for example, the number of letters contained in 3,000 books, each of 500 pages.
So even if you had 3,000 users, it would mean that the session data of each user would be 
about 1,000,000 bytes (as you indicate yourself below). Which means that each time one of 
  these users hits the system, Tomcat would need to read and load 1 MB of data just to 
retrieve this user's previous session data, without even having done anything yet for this 
user and his present request.  One may wonder how fast this server is expected to be, if 
it handles 3,000 user sessions simultaneously ?

So let's say that I am just curious as to what the application is.

Where I do object :

Christopher Schultz wrote:
...
> 
> 2. Caches. This may be something that is often not considered for a Perl
>    hacker such as yourself, where webapps tend to be scripts that run
>    once and then terminate. 

Wrong.  I am also a mod_perl hacker. In a mod_perl environment, scripts (or handlers) do 
not "terminate", and memory is not recycled (this is even an inconvenient of mod_perl, and 
something to watch when designing mod_perl applications).

So I am not objecting to using 3000 MB of Heap, I am just curious.
If someone like Eric Robinson can run a non-trivial multi-user Tomcat application with an 
average 64 MB of Heap and you can do pretty much the same, then I am curious as to which 
Tomcat application (or situation) may require 3,000 MB of Heap, which is 50 times more.

A secondary motive for my question to the OP, was to find out whether this size was really 
the result of a rational calculation (or experience), or just some number plucked out of 
the air.
RAM prices are fickle, but let's say that for server-quality RAM, one currently pays 25 
US$ per GB.
And we do not know who the OP works for, but say he is talking about 1,000 Tomcat servers.
Saving 1 GB of Heap to run his applications would thus mean saving 25,000 US$.
I believe it is worth asking the question.


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