Array subset uses twice as much memory

Question

I have been chasing a problem with running out of memory when manipulating large ammounts of acquired data.
My attached vi exhibits some very strange behavior.
My original code used "Array Subset" to clear the data in a shift register.
My revised code just uses an empty constant.
Question #1. Why should it take at least double (perhaps triple) the ammount of memory to store data using the Array subset method.
and.. Why is the memory allocated before the "Array subset" is used.
Question #2. Why am I seeing significant residual memory usage that is not being re-allocated
Labview Version 9.0.1 (32-bit)
iTm - Senior Systems Engineer
uses: LABVIEW 2012 SP1 x86 on Windows 7 x64. cFP, cRIO, PXI-RT
Attachments:
Strange memory Allocation.vi ‏21 KB
memusage.PNG ‏17 KB

Answer 1

OK,
The origins of this discovery was unexpected memory "behavior" in an application containing in excess of 1250 vi's and is attached to NI-DAq's, CAN and GPIB based hardware.
We were storing 6 minutes of 50 channels sampled at 5khz and recived an out of memory error.
To stop it failing, we reduced the sample rate to 1khz and gathered some metrics
We did the calculatons on how much memory it should take to store this many samples (360x50x1000x8) = 144 meg
The memory profiler was showing that on first run the memory would rise to an additional 432 meg at the end of sampling and at the point where the shift register was "zeroed" it would drop back to only 144 meg. On the next run it would rise back to 432Meg again.
For intellectual property and simplicity reasons, I wrote a basic VI to demonstrate the problem we found.  I was not expecting it to be critqued for programming methods or whether or not it was a valid application.
The Fundamental problem is that Labview should not allocate 3 times the memory required and not give back a third of it on completion.  Debug or otherwise.
The condensed .vi was first written without the diagram disable, which was added later as a tool to aid peers and NI LV Guru's a way to easily see the problem.
On another note, Why doesn't Labview access virtual memory to store this data instead of using RAM and running out?
We are planning a code extetion to sream the data to TDMS to compensate for this "characteristic".
iTm - Senior Systems Engineer
uses: LABVIEW 2012 SP1 x86 on Windows 7 x64. cFP, cRIO, PXI-RT
Attachments:
Lost Memory.PNG ‏69 KB