Making Replication Robust

David Carter dpc22 at
Tue Oct 9 08:57:16 EDT 2007

On Mon, 8 Oct 2007, Rudy Gevaert wrote:

> Note, we are running 2.3.7, I'm going to upgrade when 2.3.10 is out. 
> We have replication in place, but daren't use it.  If I have a method to 
> check if the replica is in sync then I'll dare to do a fail over.

I do this using "-v -v" to sync_client, which gives a running commentary
about just what is going on:

   cyrus-28[cyrus:~]$ replicate -s cyrus-27 -v -v -u dpc99
   USER dpc99
      USER_ALL dpc99
      SELECT user.dpc99
      UPLOAD [1 msgs]

A very high tech "grep -v USER /tmp/out" picks out actual updates.

This is one of the things which got dropped when replication was merged 
into 2.3 (my original implementation just didn't fit cleanly). I would 
like to put something similar into 2.3, as this is a quick and easy way to 
check for consistency while fixing up problems. A "dry run" mode which 
supresses updates would also be useful, although probably more work.

The kind of random sampling which Fastmail do probably wouldn't hurt as an 
extra sanity check.

David Carter                             Email: David.Carter at
University Computing Service,            Phone: (01223) 334502
New Museums Site, Pembroke Street,       Fax:   (01223) 334679
Cambridge UK. CB2 3QH.

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