[ python-Bugs-1389051 ] imaplib causes excessive fragmentation for large documents

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Bugs item #1389051, was opened at 2005-12-23 19:11
Message generated for change (Comment added) made by effbot
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https://sourceforge.net/tracker/?func=detail&atid=105470&aid=1389051&group_id=5470

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Category: Python Library
Group: Python 2.4
Status: Open
Resolution: None
Priority: 5
Submitted By: Fredrik Lundh (effbot)
Assigned to: Nobody/Anonymous (nobody)
Summary: imaplib causes excessive fragmentation for large documents

Initial Comment:
When fetching large documents via SSL, the imaplib 
attempts to read it all in one chunk, but the SSL 
socket layer only returns ~16k at a time.

The result is that Python will end up allocating, say, 
a 15 megabyte block, shrink it to a few kilobytes, 
occasionally allocate a medium-sized block (to hold 
the list of chunks), and repeat this again and again 
and again.  Not all malloc implementations can reuse 
the (15 megabytes minus a few kilobyte) block when 
allocating the next 15 megabyte block.  In a worst 
case scenario, you'll need some 13 gigabytes of 
virtual memory to read a 15 megabyte message...

A simple solution is to change

    data = self.sslobj.read(size-read)

to

    data = self.sslobj.read(min(size-read, 16384))

For more on this, see this thread:

http://groups.google.com/group/comp.lang.python/browse_
frm/thread/3737500bac287575/d715bf614a86e786

</F>

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>Comment By: Fredrik Lundh (effbot)
Date: 2005-12-25 11:57

Message:
Logged In: YES 
user_id=38376

As noted in that thread, the same problem applies to non-
SSL accesses.  The problematic line is:

data = self._sock.recv(recv_size) 

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