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From Anuj Wadehra <anujw_2...@yahoo.co.in>
Subject Inconsistent Reads after Restoring Snapshot
Date Tue, 26 Apr 2016 02:26:10 GMT
Hi,
We have 2.0.14. We use RF=3 and read/write at Quorum. Moreover, we dont use incremental backups.
As per the documentation at https://docs.datastax.com/en/cassandra/2.0/cassandra/operations/ops_backup_snapshot_restore_t.html ,
if i need to restore a Snapshot on SINGLE node in a cluster, I would run repair at the end.
But while the repair is going on, reads may get inconsistent.

Consider following scenario:10 AM Daily Snapshot taken of node A and moved to backup location11
AM A record is inserted such that node A and B insert the record but there is a mutation drop
on node C.1 PM Node A crashes and data is restored from latest 10 AM snapshot. Now, only Node
B has the record.
Now, my question is:
Till the repair is completed on node A,a read at Quorum may return inconsistent result based
on the nodes from which data is read.If data is read from node A and node C, nothing is returned
and if data is read from node A and node B, record is returned. This is a vital point which
is not highlighted anywhere.

Please confirm my understanding.If my understanding is right, how to make sure that my reads
are not inconsistent while a node is being repair after restoring a snapshot.
I think, autobootstrapping the node without joining the ring till the repair is completed,
is an alternative option. But snapshots save lot of streaming as compared to bootstrap.
Will incremental backups guarantee that 
ThanksAnuj

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