doveadm sync out of memory

[Casey Stone]

Hello:

I've been looking forward to getting my mail server up to Dovecot 2.2+ to be able to use the sync mechanism. I run my own mail server just for myself, with a few different accounts, and want to keep a master and backup server in sync. 

I'm running the Ubuntu server 14.04.1 mail stack which features Dovecot 2.2.9 (and Postfix). My setup is to use system users (userdb passwd / passdb pam) with ~/Maildir. I'll post full sanitized output of dovecot -n if it seems necessary. I have not enabled any plugins (do I need the replicator plugin active?) I have in my conf a doveadm_password defined.

Anyway, after setting up an ssl listener on the main machine and after considerable struggles with SSL, I was able to run doveadm sync from the backup server successfully for a small mailbox (around 78 MB) with this command:

doveadm sync -R tcps:mainserver.example.com:12345

Since I run this command as the system user on the backup server (same system users as main server) it 'just works' for the correct single user with no further options required. My plan is to run a daily cron job to sync once daily for each user.

The problem is when I try to sync a larger mailbox, say 1 GB, dsync-server on the remote (master) machine throws fatal error 83 Out of Memory. I already raised vsz_limit to 512 MB. Problems probably arise with mailboxes around 200 MB though I haven't tested specifically. So my question is, is this expected and I will need to give my VM much more memory to be able to use dovecot sync, or do I have something set wrong, or is it a bug?

Thanks for your help.