cassandra-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Richard Low <>
Subject Re: Reducing the number of vnodes
Date Mon, 05 Aug 2013 12:17:44 GMT
On 5 August 2013 12:30, Christopher Wirt <> wrote:

I’m thinking about reducing the number of vnodes per server.****
> ** **
> We have 3 DC setup – one with 9 nodes, two with 3 nodes each.****
> ** **
> Each node has 256 vnodes. We’ve found that repair operations are beginning
> to take too long.****
> ** **
> Is reducing the number of vnodes to 64/32 likely to help our situation?

Unlikely.  The amount of time repair takes only depends on the number of
vnodes if you have a tiny amount of data.  If you have 256 vnodes and not
much more than 256 * num_nodes rows, the overhead of splitting up the
repairs into separate ranges for each vnode is significant.  However, once
your dataset becomes bigger than this trivial amount, the vnode overhead of
repair becomes totally insignificant.

The main reasons for slow repair are lots of data or lots of data out of
sync.  You can tell how much is out of sync by looking in the logs - it
will say how many ranges within each vnode range need repairing.


View raw message