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https://issues.apache.org/jira/browse/COUCHDB-1405?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13204450#comment-13204450
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Robert Newson commented on COUCHDB-1405:
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I know, from bitter experience, that timekeeping in some hypervisors is pretty
lousy. Specifically, I've experienced every kind of clock-goes-wrong event
inside VMWare guests.
I doubt that erlang:now()'s behavior of never returning the same value twice is
at fault here (it's certainly *not* just returning the CMOS value but the
difference should be negligible). I'd further argue that attempting to get an
absolute guarantee of consistent time across a cluster is doomed to failure.
You can get very close but unless you're prepared to synchronously consult a
single external time authority every time (and to fail when it's unavailable)
there will be mistakes. The only alternative I've found is to implement a
fault-tolerant consensus mechanism (oh, it's that easy, huh?). The better
solution is to not require this kind of synchronization in the first place.
In non-virtual situations, NTP is your friend. In virtual situations, NTP is
your enemy. Your virtual host should be configured to set the time in all
guests and the guests should generally *not* use NTP. Since the guests are not
necessarily getting every clock cycle they believe they are, the NTP auto
correction algorithms can get confused, ironically making things worse, not
better.
> error generating document id with utc_random
> --------------------------------------------
>
> Key: COUCHDB-1405
> URL: https://issues.apache.org/jira/browse/COUCHDB-1405
> Project: CouchDB
> Issue Type: Bug
> Components: Database Core
> Affects Versions: 1.1.1
> Environment: Windows 7, 64-bit, running as virtual pc in hyper-v
> Reporter: André Bögge
> Labels: Hyper-V
>
> I use the utc_random algorithm for generating document ids. So it's possible
> for me to calculate time and date out of the id in my client application.
> After running CouchDB for about a month i got a difference between system
> time and calculated time of id of about half an hour. I restarted the
> database and even then i got a difference about 1 minute.
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