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Re: Repair scheduling tools


I understand the merits of both approaches. In working with other DBs In the “old country” of SQL, we often had to write indexing sequences manually for important tables. It was “built into the product” but in order to leverage the maximum benefits of indices we had to have different indices other than the clustered (physical index). The process still sucked. It’s never perfect.

The JVM is already fraught with GC issues and putting another process being managed in the same heapspace is what I’m worried about. Technically the process could be in the same binary but started as a side Car or in the same main process.

Consider a process called “cassandra-agent” that’s sitting around with a scheduler based on config or a Cassandra table. Distributed in the same release. Shell / service scripts would start it. The end user knows it only by examining the .sh files. This opens possibilities of including a GUI hosted in the same process without cluttering the core coolness of Cassandra.

Best,

--
Rahul Singh
rahul.singh@xxxxxxxx

Anant Corporation

On Apr 4, 2018, 2:50 AM -0400, Dor Laor <dor@xxxxxxxxxxxx>, wrote:
> We at Scylla, implemented repair in a similar way to the Cassandra reaper.
> We do
> that using an external application, written in go that manages repair for
> multiple clusters
> and saves the data in an external Scylla cluster. The logic resembles the
> reaper one with
> some specific internal sharding optimizations and uses the Scylla rest api.
>
> However, I have doubts it's the ideal way. After playing a bit with
> CockroachDB, I realized
> it's super nice to have a single binary that repairs itself, provides a GUI
> and is the core DB.
>
> Even while distributed, you can elect a leader node to manage the repair in
> a consistent
> way so the complexity can be reduced to a minimum. Repair can write its
> status to the
> system tables and to provide an api for progress, rate control, etc.
>
> The big advantage for repair to embedded in the core is that there is no
> need to expose
> internal state to the repair logic. So an external program doesn't need to
> deal with different
> version of Cassandra, different repair capabilities of the core (such as
> incremental on/off)
> and so forth. A good database should schedule its own repair, it knows
> whether the shreshold
> of hintedhandoff was cross or not, it knows whether nodes where replaced,
> etc,
>
> My 2 cents. Dor
>
> On Tue, Apr 3, 2018 at 11:13 PM, Dinesh Joshi <
> dinesh.joshi@xxxxxxxxx.invalid> wrote:
>
> > Simon,
> > You could still do load aware repair outside of the main process by
> > reading Cassandra's metrics.
> > In general, I don't think the maintenance tasks necessarily need to live
> > in the main process. They could negatively impact the read / write path.
> > Unless strictly required by the serving path, it could live in a sidecar
> > process. There are multiple benefits including isolation, faster iteration,
> > loose coupling. For example - this would mean that the maintenance tasks
> > can have a different gc profile than the main process and it would be ok.
> > Today that is not the case.
> > The only issue I see is that the project does not provide an official
> > sidecar. Perhaps there should be one. We probably would've not had to have
> > this discussion ;)
> > Dinesh
> >
> > On Tuesday, April 3, 2018, 10:12:56 PM PDT, Qingcun Zhou <
> > zhouqingcun@xxxxxxxxx> wrote:
> >
> > Repair has been a problem for us at Uber. In general I'm in favor of
> > including the scheduling logic in Cassandra daemon. It has the benefit of
> > introducing something like load-aware repair, eg, only schedule repair
> > while no ongoing compaction or traffic is low, etc. As proposed by others,
> > we can expose keyspace/table-level configurations so that users can opt-in.
> > Regarding the risk, yes there will be problems at the beginning but in the
> > long run, users will appreciate that repair works out of the box, just like
> > compaction. We have large Cassandra deployments and can work with Netflix
> > folks for intensive testing to boost user confidence.
> >
> > On the other hand, have we looked into how other NoSQL databases do repair?
> > Is there a side car process?
> >
> >
> > On Tue, Apr 3, 2018 at 9:21 PM, sankalp kohli <kohlisankalp@xxxxxxxxx
> > wrote:
> >
> > > Repair is critical for running C* and I agree with Roopa that it needs to
> > > be part of the offering. I think we should make it easy for new users to
> > > run C*.
> > >
> > > Can we have a side car process which we can add to Apache Cassandra
> > > offering and we can put this repair their? I am also fine putting it in
> > C*
> > > if side car is more long term.
> > >
> > > On Tue, Apr 3, 2018 at 6:20 PM, Roopa Tangirala <
> > > rtangirala@xxxxxxxxxxx.invalid> wrote:
> > >
> > > > In seeing so many companies grapple with running repairs successfully
> > in
> > > > production, and seeing the success of distributed scheduled repair here
> > > at
> > > > Netflix, I strongly believe that adding this to Cassandra would be a
> > > great
> > > > addition to the database. I am hoping, we as a community will make it
> > > easy
> > > > for teams to operate and run Cassandra by enhancing the core product,
> > and
> > > > making the maintenances like repairs and compactions part of the
> > database
> > > > without external tooling. We can have an experimental flag for the
> > > feature
> > > > and only teams who are confident with the service can enable them,
> > while
> > > > others can fall back to default repairs.
> > > >
> > > >
> > > > *Regards,*
> > > >
> > > > *Roopa Tangirala*
> > > >
> > > > Engineering Manager CDE
> > > >
> > > > *(408) 438-3156 - mobile*
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > On Tue, Apr 3, 2018 at 4:19 PM, Kenneth Brotman <
> > > > kenbrotman@xxxxxxxxx.invalid> wrote:
> > > >
> > > > > Why not make it configurable?
> > > > > auto_manage_repair_consistancy: true (default: false)
> > > > >
> > > > > Then users can use the built in auto repair function that would be
> > > > created
> > > > > or continue to handle it as now. Default behavior would be "false"
> > so
> > > > > nothing changes on its own. Just wondering why not have that option?
> > > It
> > > > > might accelerate progress as others have already suggested.
> > > > >
> > > > > Kenneth Brotman
> > > > >
> > > > > -----Original Message-----
> > > > > From: Nate McCall [mailto:zznate.m@xxxxxxxxx]
> > > > > Sent: Tuesday, April 03, 2018 1:37 PM
> > > > > To: dev
> > > > > Subject: Re: Repair scheduling tools
> > > > >
> > > > > This document does a really good job of listing out some of the
> > issues
> > > of
> > > > > coordinating scheduling repair. Regardless of which camp you fall
> > into,
> > > > it
> > > > > is certainly worth a read.
> > > > >
> > > > > On Wed, Apr 4, 2018 at 8:10 AM, Joseph Lynch <joe.e.lynch@xxxxxxxxx
> > > > > wrote:
> > > > > > I just want to say I think it would be great for our users if we
> > > moved
> > > > > > repair scheduling into Cassandra itself. The team here at Netflix
> > has
> > > > > > opened the ticket
> > > > > > <https://issues.apache.org/jira/browse/CASSANDRA-14346
> > > > > > and have written a detailed design document
> > > > > > <https://docs.google.com/document/d/1RV4rOrG1gwlD5IljmrIq_
> > > t45rz7H3xs9G
> > > > > > bFSEyGzEtM/edit#heading=h.iasguic42ger
> > > > > > that includes problem discussion and prior art if anyone wants to
> > > > > > contribute to that. We tried to fairly discuss existing solutions,
> > > > > > what their drawbacks are, and a proposed solution.
> > > > > >
> > > > > > If we were to put this as part of the main Cassandra daemon, I
> > think
> > > > > > it should probably be marked experimental and of course be
> > something
> > > > > > that users opt into (table by table or cluster by cluster) with the
> > > > > > understanding that it might not fully work out of the box the first
> > > > > > time we ship it. We have to be willing to take risks but we also
> > have
> > > > > > to be honest with our users. It may help build confidence if a few
> > > > > > major deployments use it (such as Netflix) and we are happy of
> > course
> > > > > > to provide that QA as best we can.
> > > > > >
> > > > > > -Joey
> > > > > >
> > > > > > On Tue, Apr 3, 2018 at 10:48 AM, Blake Eggleston
> > > > > > <beggleston@xxxxxxxxx
> > > > > > wrote:
> > > > > >
> > > > > > > Hi dev@,
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > > > The question of the best way to schedule repairs came up on
> > > > > > > CASSANDRA-14346, and I thought it would be good to bring up the
> > idea
> > > > > > > of an external tool on the dev list.
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > > > Cassandra lacks any sort of tools for automating routine tasks
> > that
> > > > > > > are required for running clusters, specifically repair. Regular
> > > > > > > repair is a must for most clusters, like compaction. This means
> > > that,
> > > > > > > especially as far as eventual consistency is concerned, Cassandra
> > > > > > > isn’t totally functional out of the box. Operators either need to
> > > > > > > find a 3rd party solution or implement one themselves. Adding this
> > > to
> > > > > > > Cassandra would make it easier to use.
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > > > Is this something we should be doing? If so, what should it look
> > > like?
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > > > Personally, I feel like this is a pretty big gap in the project
> > and
> > > > > > > would like to see an out of process tool offered. Ideally,
> > Cassandra
> > > > > > > would just take care of itself, but writing a distributed repair
> > > > > > > scheduler that you trust to run in production is a lot harder than
> > > > > > > writing a single process management application that can failover.
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > > > Any thoughts on this?
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > > > Thanks,
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > > > Blake
> > > > > > >
> > > > > > >
> > > > >
> > > > > ------------------------------------------------------------
> > ---------
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> > > > >
> > > > >
> > > > > ------------------------------------------------------------
> > ---------
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> > > > >
> > > > >
> > > >
> > >
> >
> >
> >
> > --
> > Thank you & Best Regards,
> > --Simon (Qingcun) Zhou
> >