RE: [Prevayler-discussion] Memory size

[Sheppard M. C. AFRL/I. <Mar...@rl...>]

Hello all,

I never seem to be able to get to www.prevayler.org  Anyone else have this
problem?

Marty.

-----Original Message-----
From: pre...@li...
[mailto:pre...@li...] On Behalf Of
Justin Sampson
Sent: Thursday, September 30, 2004 12:54 PM
To: pre...@li...
Subject: Re: [Prevayler-discussion] Memory size


On Thu, 30 Sep 2004, Vitor Fernando Pamplona wrote:

> > What do you mean by "database"?
>
> One java.util.List that have my 3000 instances? :D
>
> I ask because if Prevayler duplicate this java.util.List on each 
> Transaction, i'll need more memory on machine (List.size() * 100 * 2). 
> Correct?

Yes, you'll need enough memory two hold to copies of the list and all the
objects it contains. It's not copied on each transaction; ideally it's
copied once for the first transaction and then never again (since it's
running all the same transactions as the main copy). However, if a
transaction throws a RuntimeException, the system will be copied again to
"rollback" that transaction. This means that the actual peak memory
requirement will be roughly 3 times, depending on how you serialize
snapshots, because the copying involves taking an in-memory snapshot and
then recovering the copy from the snapshot.

(I've got a couple of ideas for eliminating that extra peak memory usage.)

If this is really a problem (try it first), you can turn off the royal food
taster (a.k.a the strict transaction censor). Be sure you understand the
implications, of course. There's an older discussion here:

http://www.prevayler.org/wiki.jsp?topic=RollbackIsNeedless

Justin


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