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
