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✏️ Editing: FAQ.Memory.txt

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$Id: FAQ.Memory.txt,v 1.8 2018/08/31 13:29:53 gilles Exp gilles $

This document is also available online at
https://imapsync.lamiral.info/FAQ.d/
https://imapsync.lamiral.info/FAQ.d/FAQ.Memory.txt

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             Imapsync tips about memory issues.
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Q. I got an "Out of memory" error message then imapsync crashes.
   How to fix that?

R0. Add option --debugmemory to debug memory issues.
    On Windows this option uses a DOS command similar to:

tasklist /NH /FO CSV | findstr imapsync

On Unix it uses:
    
        ps -o vsz -p PID_of_imapsync  # value is in KB

Similar to:
    
        ps -ax -o vsz,comm | grep imapsync

Use those commands in a DOS window or a Unix shell in order
    to monitor a imapsync run you know it will crash. 
    The goal is to detect the memory limit, when and how it happens.
    
    * Is the "final" amount near the total RAM available or 
      just a small part of it?
    * Does the rise of memory consumption happens suddenly 
      or along the sync?

R1. It's probably a very big message on the host1 account.
   Before imapsync release 1.688 memory usage is at least 5 times 
   the biggest message size. then 2 times with release 1.688.
   So a 700 MB message will crunch 3.5 GB of memory.
   Starting with 1.688 it  will crunch 1.4 GB of memory.

R2. To check if the problem is a big message crunching to much 
   memory, add --maxsize 50_000_000, this will limit the message
   size treated to 50 MB. If the sync succeed while limiting 
   messages sizes it's probably is a big message crunching to much
   memory issue. Possible solutions:
   * Try on another host
   * Buy memory
   * Build imapsync.exe binary 64bits

R3. If R2 shows that the memory issue is not a big message crunching 
    too much memory, then it can be imapsync using too much memory
    to identify messages (a very big folder served by a
    very talkative imap server). A possible solution is to use
    the option --useuid. If it still fails, I have no clue.
    If you have time, drop me a note.

R4. Usually "Out of memory" errors are related to old days,
   to old Mail::IMAPClient module releases, before 3.26.
   At that time memory usage was around 17 times the biggest message.
   Look at imapsync output first lines to get the Mail::IMAPClient 
   release used. Then upgrade Mail::IMAPClient Perl module if needed.

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MR SKB