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To be honest this something you should just get SQL server to do without CFML.
However, if you are definitely going down this path then there are a few things
you should know. In Java Strings are immutable this means that you cannot
change a string once it has been assigned. So if you do things like:-
<cfscript>
myString = "Simon";
myString = myString & " Baynes";
writeoutput(myString);
</cfscript>
This doesn't actually update the variable but create a new variable in memory
that is the result of the second assignment. The old value will sit in memory
waiting to be Garbage Collected. I am sure you can now see that if you are
looping through a query doing loads of append statements then it's going to
create lots of information in memory.
There is a Java class for this very type of operation called a StringBuilder
that manages this internally to reduce the memory usage.
<cfscript>
oXml = createObject("java","java.lang.StringBuilder").init();
oXml.append("Simon");
oXml.append(" Baynes");
writeoutput(oXml.toString());
</cfscript>
When using this for multiple append statements it'll save you lots of memory!
Having said that creating a 50Meg xml file will use at the very least 50Meg of
memory for that request which is not really what App Servers like Railo or CF
are for hence the advice of doing the whole job in SQL server.
Hope that helps!
Simon
Simon Baynes
www.simonbaynes.com
Free online storage you can access anywhere:-
http://www.simonbaynes.com/getsugarsync
LinkedIn profile:- http://www.linkedin.com/in/simonbaynes
-----Original Message-----
From: Rich Wild <[email protected]>
Date: Sun, 6 Dec 2009 19:55:30
To: Coldfusion Development<[email protected]>
Subject: [CF-Dev] Railo, Resin and large text variables = out of memory
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Wotcha,
I'm using Railo 3.1.2 + Resin 3.1 on an II6 Server. Its all been brill on
toast, thus far.
Now, on this particular website, they have a requirement to build large XML
files produced from SQL Server databases. These XML files can be over 50Mb
in size.
I'm running my SQL statements and building the XML using cfsavecontent
before saving out using cffile and zipping with cfzip. I figured producing
them as appended string variables as opposed to XML variables would save
time, processing and memory.
However, I inconsistently get errors whilst building these files:
Railo 3.1.2.001 Error (Java.lang.outofmemoryerror) - Java heap space
Hmmm. That's not good.
I tracked down the resin.conf file and changed
<jvm-arg>-Xmx256m</jvm-arg>
to
<jvm-arg>-Xmx512m</jvm-arg>
to try and increase the memory available. I still get the errors.
Anyone have any clues how I can make this go away? I'm sure a comparable
CF8/9 server on the same hardware config machine wouldn't have this problem.
They're not THAT big XML files.
Cheers,
Rich
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