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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