Probably not beneficial, I wouldn't do it. Not a fan of multi-tenancy with Cassandra unless the use cases are so small that your noisy neighbor problem is not very noisy at all. For those cases I don't know what you get from Cassandra other than a cool resume.
On Wed, Oct 23, 2019 at 12:41 PM Reid Pinchback <rpinchb...@tripadvisor.com> wrote: > I haven’t seen much evidence that larger cluster = more performance, plus > or minus the statistics of speculative retry. It horizontally scales for > storage definitely, and somewhat for connection volume. If anything, per > Sean’s observation, you have less ability to have a stable tuning for a > particular usage pattern. > > > > Try to have a mental picture of what you think is happening in the JVM > while Cassandra is running. There are short-lived objects, medium-lived > objects, long/static-lived objects, and behind the scenes some degree of > read I/O and write I/O against disk. Garbage collectors struggle badly > with medium-lived objects, but Cassandra really depends a great deal on > those. If you merge two clusters together, within any one node you still > have the JVM size and disk architecture you had before, but you are adding > competition on fixed resources and potentially in the very way they find > most difficult to handle. > > > > If those resources were heavily underutilized, like Sean’s point about > merging small apps together, then sure. But if those two clusters of yours > are already showing that they experience significant load, then you are > unlikely to improve anything, far more likely to end up worse off. GC > overhead and compaction flushes to disk are your challenges; merging two > clusters doesn’t change the physics of those two areas, but could increase > the demand on them. > > > > The only caveat to all of the above I can think of is if there was a > fault-tolerance story motivating the merging. Like “management wants us in > two AZs in AWS, but lacks the budget for more instances, and each pool by > itself is too small for us to come up with a 2 rack organization that makes > sense”. > > > > R > > > > *From: *Osman YOZGATLIOĞLU <osman.yozgatlio...@kron.com.tr> > *Reply-To: *"user@cassandra.apache.org" <user@cassandra.apache.org> > *Date: *Wednesday, October 23, 2019 at 10:40 AM > *To: *"user@cassandra.apache.org" <user@cassandra.apache.org> > *Subject: *Re: merge two cluster > > > > *Message from External Sender* > > Sorry, missing question; > > Actually I'm asking this for performance perspective. At application level > both cluster used at the same time and approx same level. Inserted data > inserted to both cluster, different parts of course. > > If I merge two cluster, can I gain some performance improvements? Like > raid stripes, more disk, more stripe, more speed.. > > > > Regards > > On 23.10.2019 17:30, Durity, Sean R wrote: > > Beneficial to whom? The apps, the admins, the developers? > > > > I suggest that app teams have separate clusters per application. This > prevents the noisy neighbor problem, isolates any security issues, and > helps when it is time for maintenance, upgrade, performance testing, etc. > to not have to coordinate multiple app teams at the same time. Also, an > individual cluster can be tuned for its specific workload. Sometimes, > though, costs and data size push us towards combining smaller apps owned by > the same team onto a single cluster. Those are the exceptions. > > > > As a Cassandra admin, I am always trying to scale the ability to admin > multiple clusters without just adding new admins. That is an on-going task, > dependent on your operating environment. > > > > Also, because every table has a portion of memory (memtable), there is a > practical limit to the number of tables that any one cluster should have. I > have heard it is in the low hundreds of tables. This puts a limit on the > number of applications that a cluster can safely support. > > > > > > Sean Durity – Staff Systems Engineer, Cassandra > > > > *From:* Osman YOZGATLIOĞLU <osman.yozgatlio...@kron.com.tr> > <osman.yozgatlio...@kron.com.tr> > *Sent:* Wednesday, October 23, 2019 6:23 AM > *To:* user@cassandra.apache.org > *Subject:* [EXTERNAL] merge two cluster > > > > Hello, > > I have two cluster and both contains different data sets with different > node counts. > > Would it be beneficial to merge two cluster? > > > > Regards, > > Osman > > > ------------------------------ > > > The information in this Internet Email is confidential and may be legally > privileged. It is intended solely for the addressee. Access to this Email > by anyone else is unauthorized. If you are not the intended recipient, any > disclosure, copying, distribution or any action taken or omitted to be > taken in reliance on it, is prohibited and may be unlawful. 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