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From David Fisher <dfis...@jmlafferty.com>
Subject Re: [OT] Tomcat unexpectedly shuts down
Date Tue, 10 Aug 2010 22:12:02 GMT
Hi Andre,

> 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.

I will give you an example of two reasons for a large heap -

(1) You host a large data set that you treat as a global in memory database achieving lighting
quick sorts and filters across any column. This consumes a large amount of memory for the
life of the JVM. Daily refreshes require double space in transition. The size of the heap
will limit the size of the data set.

(2) You need to produce large Excel spreadsheets or Powerpoint decks using Apache POI. Due
to the binary nature of the file formats everything is constructed in memory and the memory
footprint of the Java objects is much larger. The XML versions don't give you any relief as
they are Zip files. This means you need large amounts of space for short periods of time.
Again more memory means the more head room you have for these requests. You have to know your
app well to know if you have enough room for the very occasional large request. If that can
be too big then you will need to build an execution queue of some type behind your web app.

Regards,
Dave
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