What is recommended vnodes now? I read 8 in later cassandra 3.x Is the new recommendation 4 now even in version 3.x (asking for 3.11)? Thanks
On Fri, Jan 31, 2020 at 9:49 AM Durity, Sean R <sean_r_dur...@homedepot.com> wrote: > These are good clarifications and expansions. > > > > Sean Durity > > > > *From:* Anthony Grasso <anthony.gra...@gmail.com> > *Sent:* Thursday, January 30, 2020 7:25 PM > *To:* user <user@cassandra.apache.org> > *Subject:* Re: [EXTERNAL] How to reduce vnodes without downtime > > > > Hi Maxim, > > > > Basically what Sean suggested is the way to do this without downtime. > > > > To clarify the, the *three* steps following the "Decommission each node > in the DC you are working on" step should be applied to *only* the > decommissioned nodes. So where it say "*all nodes*" or "*every node*" it > applies to only the decommissioned nodes. > > > > In addition, the step that says "Wipe data on all the nodes", I would > delete all files in the following directories on the decommissioned nodes. > > - data (usually located in /var/lib/cassandra/data) > - commitlogs (usually located in /var/lib/cassandra/commitlogs) > - hints (usually located in /var/lib/casandra/hints) > - saved_caches (usually located in /var/lib/cassandra/saved_caches) > > > > Cheers, > > Anthony > > > > On Fri, 31 Jan 2020 at 03:05, Durity, Sean R <sean_r_dur...@homedepot.com> > wrote: > > Your procedure won’t work very well. On the first node, if you switched to > 4, you would end up with only a tiny fraction of the data (because the > other nodes would still be at 256). I updated a large cluster (over 150 > nodes – 2 DCs) to smaller number of vnodes. The basic outline was this: > > > > - Stop all repairs > - Make sure the app is running against one DC only > - Change the replication settings on keyspaces to use only 1 DC > (basically cutting off the other DC) > - Decommission each node in the DC you are working on. Because the > replication setting are changed, no streaming occurs. But it releases the > token assignments > - Wipe data on all the nodes > - Update configuration on every node to your new settings, including > auto_bootstrap = false > - Start all nodes. They will choose tokens, but not stream any data > - Update replication factor for all keyspaces to include the new DC > - I disabled binary on those nodes to prevent app connections > - Run nodetool reduild with -dc (other DC) on as many nodes as your > system can safely handle until they are all rebuilt. > - Re-enable binary (and app connections to the rebuilt DC) > - Turn on repairs > - Rest for a bit, then reverse the process for the remaining DCs > > > > > > > > Sean Durity – Staff Systems Engineer, Cassandra > > > > *From:* Maxim Parkachov <lazy.gop...@gmail.com> > *Sent:* Thursday, January 30, 2020 10:05 AM > *To:* user@cassandra.apache.org > *Subject:* [EXTERNAL] How to reduce vnodes without downtime > > > > Hi everyone, > > > > with discussion about reducing default vnodes in version 4.0 I would like > to ask, what would be optimal procedure to perform reduction of vnodes in > existing 3.11.x cluster which was set up with default value 256. Cluster > has 2 DC with 5 nodes each and RF=3. There is one more restriction, I could > not add more servers, nor to create additional DC, everything is physical. > This should be done without downtime. > > > > My idea for such procedure would be > > > > for each node: > > - decommission node > > - set auto_bootstrap to true and vnodes to 4 > > - start and wait till node joins cluster > > - run cleanup on rest of nodes in cluster > > - run repair on whole cluster (not sure if needed after cleanup) > > - set auto_bootstrap to false > > repeat for each node > > > > rolling restart of cluster > > cluster repair > > > > Is this sounds right ? My concern is that after decommission, node will > start on the same IP which could create some confusion. > > > > Regards, > > Maxim. > > > ------------------------------ > > > The information in this Internet Email is confidential and may be legally > privileged. It is intended solely for the addressee. 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