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To: python-list@python.org
From: Dennis Lee Bieber <wlfraed@ix.netcom.com>
Subject: Re: Python does not take up available physical memory
Date: Fri, 19 Oct 2012 18:01:22 -0400
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On Fri, 19 Oct 2012 12:08:53 -0500, Pradipto Banerjee
<pradipto.banerjee@adainvestments.com> declaimed the following in
gmane.comp.python.general:

> Hi,
> 
> I am trying to read a file into memory. The size of the file is around 1 GB. I have a 3GB memory PC and the Windows Task Manager shows  2.3 GB available physical memory when I was trying to read the file. I tried to read the file as follows:

1)	32-bit Windows OS can only physically address 4GB BUT
2)	Unless you have a SERVER version of windows, the most allocated to a
user process is 2GB (there is a boot-time parameter which can configure
WinXP [for example] to allow 3GB to user processes -- the last GB is
always reserved for the OS)

> Is there any reason why python can't read a 1GB file in memory even when a 2.3 GB physical memory is available? Do I need to make a change in some setting or preferences?
> 
> I am using python(x,y) distribution (python 2.7) and use Spyder as the IDE.
>
	Are you /running/ from within the IDE -- such that the Python
interpreter is considered part of the IDE address space?

	<snipped>

	My first thought would be that you should NOT be loading an entire
GB file as one chunk (for all I know, Windows low-level I/O read the
file into a OS buffer [1GB] and then tries to pass it on to the Python
memory buffer [another 1GB]... Or Python is reading in chunks -- say 1MB
at a time, and appending chunks... That means it goes "whoops, I've got
a 512MB data buffer and just read another 1MB -- better allocate a 768MB
buffer [total now is 512 + 768 + 1 => 1281MB], copy the 512MB into the
new buffer, append the 1MB, NOW free the older 512MB... You might have
the raw memory, but it may be fragmented such that the system can not
allocate a contiguous 1MB chunk).

	If .readlines() works when .read() fails, it is memory fragmentation
(each parsed line is an individual chunk of memory since the list of
lines is just a list of addresses to the lines)
-- 
	Wulfraed                 Dennis Lee Bieber         AF6VN
        wlfraed@ix.netcom.com    HTTP://wlfraed.home.netcom.com/