As long as balanced is achieved, fewer vnodes the better -- Jeff Jirsa
> On Oct 9, 2017, at 7:53 AM, Li, Guangxing <guangxing...@pearson.com> wrote: > > Jeff, > > so the key really is to keep nodes load balanced, and as long as that such > balance is achieved, using a smaller amount of vnodes does not have other > negative impact? > > Thanks. > > George > >> On Mon, Oct 9, 2017 at 8:46 AM, Jeff Jirsa <jji...@gmail.com> wrote: >> >> 256 was chosen because the original vnode allocation algorithm was random >> and fewer than 256 could lead to unbalanced nodes >> >> In 3.0 there’s a less naive algorithm to ensure more balanced >> distribution, and there 16 or 32 is probably preferable >> >> >> -- >> Jeff Jirsa >> >> >>> On Oct 9, 2017, at 7:38 AM, Li, Guangxing <guangxing...@pearson.com> >> wrote: >>> >>> Hi, >>> >>> the documentation says that '...The recommended initial value for >>> num_tokens is 256...' and this is what we did with our cluster which is >>> running Cassandra Community 2.0.9, has 3 physical nodes with replication >>> factor 3 for all keyspaces, each with 256 vnodes, each physical node has >>> about 96 GB data. We noticed that doing a repair for some keyspaces can >>> take up to 37 hours. We did some testing and reduced the number of vnodes >>> from 256 to 32 for each physical node, and we noticed that this does >> reduce >>> the amount of time to do repair quite a lot, as indicated in the >> following: >>> >>> nodetool repair command Cassandra version Number of vnodes/physical node >> Repair >>> time >>> >>> nodetool repair courseassociation associations >>> 2.0.9 >>> 256 26 hours 4 minutes >>> 32 21 hours 46 minutes >>> >>> nodetool repair userassociation associations >>> 2.0.9 >>> 256 37 hours 2 minutes >>> 32 26 hours 29 minutes >>> >>> nodetool repair orguserassociation associations >>> 2.0.9 >>> 256 13 hours 35 minutes >>> 32 6 hrs 27 minutes >>> >>> nodetool repair userorgassociation associations >>> 2.0.9 >>> 256 3 hours 26 minutes >>> 32 1 hour 39 minutes >>> >>> So using a smaller number of vnodes does reduce the repair time, but what >>> are other implications by doing so, performance? system resource >>> consumptions? Is there a general guideline on the number of vnodes we >>> should configure to? >>> >>> Thanks. >>> >>> George >> >> --------------------------------------------------------------------- >> To unsubscribe, e-mail: dev-unsubscr...@cassandra.apache.org >> For additional commands, e-mail: dev-h...@cassandra.apache.org >> >> --------------------------------------------------------------------- To unsubscribe, e-mail: dev-unsubscr...@cassandra.apache.org For additional commands, e-mail: dev-h...@cassandra.apache.org
