Ivan Bessonov created IGNITE-19028:
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Summary: Implement safe-time propagation for meta-storage
raft-group
Key: IGNITE-19028
URL: https://issues.apache.org/jira/browse/IGNITE-19028
Project: Ignite
Issue Type: Improvement
Reporter: Ivan Bessonov
For the future implementation of schema-synchronization, we need to have a
hybrid-timestamp, associated with the meta-storage.
Database schema changes are always associated with time, and proper place to
store them would be a meta-storage.
We don't have an "action request processor" that would have been a single
source of truth when it comes to new "write" commands. In case of meta-storage,
all nodes may create write commands. Assigning a time from the _hlc_ wouldn't
work - there's a chance of having out-of order events, which is really, really
bad.
In other words, timestamps should come in order. Does this mean that
meta-storage should also have its own action request processor? That's one
possibility.
Another possibility is to make leader into a timestamp-generator. This would
lead to changes in JRaft code, but still, this may be the right way to go. It
simply requires less changes to the code. We should just remember to adjust the
clock on leader's re-election, so that time would be monotonic.
By the way, if we go with the second option, it would also fit safe time
propagation in partitions.
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