#!/bin/cat
$Id: FAQ.Memory.txt,v 1.10 2025/08/05 13:49:49 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?

  These days, year 2025, memory issues are only located 
  on MacOS hosts. Other systems, Linux, Windows are okay.
  See R1 to solve memory issues on MacOS/Darwin systems.

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 rss -p PID_of_imapsync  # value is in KB

    Similar to:
    
        ps -ax -o rss,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. MacOS Darwin crunching memory issue.
    See:
    https://imapsync.lamiral.info/INSTALL.d/INSTALL.Darwin.txt
    G) Running out of memory. Memory leak. Solution.
    It's a copy/paste from
    https://github.com/imapsync/imapsync/issues/312#issuecomment-2462754676


R2. 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.

R3. 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

R4. If R3 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.

R5. 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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