[Zope] ZSyncer

Dennis Allison allison at sumeru.stanford.EDU
Thu Sep 18 13:40:32 EDT 2003


One way to help keep everything in sync is to reset the system clock
on a regular basis.  On Linux, add the following line to your 
root cron file:

47 23 * * * rdate -s time.nist.gov; /usr/sbin/hwclock --systohc

You may want to change the firing time...  the first entries 
in the table correspond to  (min, hour, day, mon, dayofweek, ...)
'*' is interpreted as 'all in range' otherwise they are interpreted
as a comma separated list of values.   The commands are fired off 
whenever the pattern defined by the first entries matches the current 
clock. The entry above, for example, goes off at thirteen minutes before 
midnight every day.  Updating once a day does a reasonable job of keeping 
everything in sync.

If you need to really syncronize the clocks, this won't do it. You need
some really heavy-duty mechanism.  (See Leslie Lamport's papers on the
topic for an explanation....)  But for Sync's purposes, it's probably OK.B

I presume there is an equivalent mechanism for Windows, but I don't know
what it is.

On Thu, 18 Sep 2003, Paul Winkler wrote:

> On Thu, Sep 18, 2003 at 08:23:28AM -0700, Sophia Grimm wrote:
> > When I synchronize using ZSyncer, very frequently the
> > indicator text beside the folder still shows as "out
> > of date" even though it is not (the date and content
> > are correct). Is this typical? And what can I do?
> > Because this happens, I am syncing a lot of folders
> > that probably don't need it.
> 
> This is a known limitation. It happens when the source
> system's clock is a bit (or a lot) ahead of the destination.
> So you modify something and immediately sync it and the destination
> modification time is returned as older than you think.
> 
> To prevent it in the future, ensure that the source and
> destination servers have their clocks set as close as
> possible.
> However, this won't help with existing objects.
> 
> Current CVS of zsyncer tries uses DublinCore timestamps
> instead of bobobase_modification_time, when possible.
> This gives better results for CMF content.
> 
> Unfortunately, it's hard to do better for most other zope
> types, because they only provide bobobase_modification_time, which is
> under control of the underlying ZODB and cannot be
> overridden by zope.
> 
> There are plans to investigate checksumming and other strategies
> for more reliably determining sync status, but currently I don't
> have much time for this.
> 
> -- 
> 
> Paul Winkler
> http://www.slinkp.com
> Look! Up in the sky! It's RASPUTINIC SCHIZOID MEGABOT!
> (random hero from isometric.spaceninja.com)
> 
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