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From Ilya Kasnacheev <ilya.kasnach...@gmail.com>
Subject Re: Metric showing how many nodes may safely leave the cluster
Date Fri, 04 Oct 2019 13:24:15 GMT
Hello!

That's a very useful metric which we already discussed in the past. This
may be called "cluster backup factor" and "effective cache backup factor".
You can look up other mentions by searching in maillist archives.

Regards,
-- 
Ilya Kasnacheev


пт, 4 окт. 2019 г. в 16:17, Ivan Rakov <ivan.glukos@gmail.com>:

> Igniters,
>
> I've seen numerous requests to find out an easy way to check whether is
> it safe to turn off cluster node. As we know, in Ignite protection from
> sudden node shutdown is implemented through keeping several backup
> copies of each partition. However, this guarantee can be weakened for a
> while in case cluster has recently experienced node restart and
> rebalancing process is still in progress.
> Example scenario is restarting nodes one by one in order to update a
> local configuration parameter. User restarts one node and rebalancing
> starts: when it will be completed, it will be safe to proceed (backup
> count=1). However, there's no transparent way to determine whether
> rebalancing is over.
>  From my perspective, it would be very helpful to:
> 1) Add information about rebalancing and number of free-to-go nodes to
> ./control.sh --state command.
> Examples of output:
>
> > Cluster  ID: 125a6dce-74b1-4ee7-a453-c58f23f1f8fc
> > Cluster tag: new_tag
> >
> --------------------------------------------------------------------------------
> > Cluster is active
> > All partitions are up-to-date.
> > 3 node(s) can safely leave the cluster without partition loss.
> > Cluster  ID: 125a6dce-74b1-4ee7-a453-c58f23f1f8fc
> > Cluster tag: new_tag
> >
> --------------------------------------------------------------------------------
> > Cluster is active
> > Rebalancing is in progress.
> > 1 node(s) can safely leave the cluster without partition loss.
> 2) Provide the same information via ClusterMetrics. For example:
> ClusterMetrics#isRebalanceInProgress // boolean
> ClusterMetrics#getSafeToLeaveNodesCount // int
>
> Here I need to mention that this information can be calculated from
> existing rebalance metrics (see CacheMetrics#*rebalance*). However, I
> still think that we need more simple and understandable flag whether
> cluster is in danger of data loss. Another point is that current metrics
> are bound to specific cache, which makes this information even harder to
> analyze.
>
> Thoughts?
>
> --
> Best Regards,
> Ivan Rakov
>
>

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