Benedict created CASSANDRA-7489:
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Summary: Track lower bound necessary for a repair, live, without
actually repairing
Key: CASSANDRA-7489
URL: https://issues.apache.org/jira/browse/CASSANDRA-7489
Project: Cassandra
Issue Type: Improvement
Reporter: Benedict
We will need a few things in place to get this right, but it should be possible
to track live what the current health of a single range is across the cluster.
If we force an owning node to be the coordinator for an update (so if a
non-smart client sends a mutation to a non-owning node, it just proxies it on
to an owning node to coordinate the update; this should tend to minimal
overhead as smart clients become the norm, and smart clients scale up to cope
with huge clusters), then each owner can maintain the oldest known timestamp it
has coordinated an update for that was not acknowledged by every owning node it
propagated it to. The minimum of all of these for a region is the lower bound
from which we need to either repair, or retain tombstones.
There are some subtleties with this, but it means tombstones can be cleared
potentially only minutes after they are generated, instead of days or weeks. It
also means even repairs can be even more incremental, only operating over
ranges and time periods we know to be potentially out of sync.
It will most likely need RAMP transactions in place, so that atomic batch
mutations are not serialized on non-owning nodes. Having owning nodes
coordinate updates is to ensure robustness in case of a single node failure -
in this case all ranges owned by the node are considered to have a lower bound
of -Inf. Without this a single node being down would result in the entire
cluster being considered out of sync.
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