Move away from simple strat for SM keyspace #4727
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Michal-Leszczynski
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VAveryanov8 and
karol-kokoszka
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SimpleStrategy is not recommended for the production environments. It also does not support tablets, which are the way towards scylla is moving (in some distant time, vnodes might even be deprecated). Because of that, it also runs into unexpected problems like #4555. Because of those reasons, we should switch from keeping SM data in SimpleStrategy to NetworkTopologyStrategy keyspace by default. For the default, single local node SM DB cluster, both strategies result in the single node containing all of SM data. For single DC SM DB cluster they are also equivalent. On the other hand, for multi DC SM DB cluster (really not recommended...), NetworkTopologyStrategy results in keeping replication_factor replicas per DC and not per cluster. This is theoretically problematic, but such setup is also problematic for SimpleStrategy, which would still replicate the data in all DCs, so it's not a new problem. Moreover, this change only defines the default SM keyspace creation. In case user has some non-default (perhaps not recommended) SM DB setup, they can always create SM keyspace manually before starting SM server to configure it to their liking. Refs #4555
…n tests Because of #4555, but also because it's better to test recommended keyspace replication strategy, we need to replace SimpleStrategy with NetworkTopologyStrategy in tests wherever possible. In case test is aiming to run against SimpleStrategy specifically, it needs to be adjusted so that it ensures that keyspace with SimpleStrategy does not use tablets. Refs #4555
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Seems reasonable to me!
I'm curios, how how will it behave with replace manager procedure in siren, e.g. when the scylla-manager schema is restored from the self-backup?
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So this PR only changes how SM keyspace is created from scratch. In terms of siren self-backup, if SM keyspace in the backup was using SimpleStrategy, during the self-restore procedure SM would create new, tmp SM keyspace with NetworkTopologyStrategy from scratch, restore SM keyspace from the backup and switch back to using the one from the backup. |
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@paszkow does the approach presented in this PR make sense to you? |
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Alternative approach to #4555.
While the other PR focused on keeping SimpleStrategy and working around its limitations, this PR goes into direction of using NetworkTopologyStrategy instead.
The reasoning for that is:
More details in the commit messages.
Merged commit messages
SimpleStrategy is not recommended for the production environments.
It also does not support tablets, which are the way towards scylla
is moving (in some distant time, vnodes might even be deprecated).
Because of that, it also runs into unexpected problems like
#4555.
Because of those reasons, we should switch from keeping SM data in
SimpleStrategy to NetworkTopologyStrategy keyspace by default.
For the default, single local node SM DB cluster, both strategies
result in the single node containing all of SM data. For single DC
SM DB cluster they are also equivalent. On the other hand, for multi
DC SM DB cluster (really not recommended...), NetworkTopologyStrategy
results in keeping replication_factor replicas per DC and not per cluster.
This is theoretically problematic, but such setup is also problematic for
SimpleStrategy, which would still replicate the data in all DCs, so it's
not a new problem. Moreover, this change only defines the default SM
keyspace creation. In case user has some non-default (perhaps not recommended)
SM DB setup, they can always create SM keyspace manually before starting
SM server to configure it to their liking.
Because of #4555, but also because
it's better to test recommended keyspace replication strategy, we need to replace
SimpleStrategy with NetworkTopologyStrategy in tests wherever possible.
In case test is aiming to run against SimpleStrategy specifically, it needs to be
adjusted so that it ensures that keyspace with SimpleStrategy does not use tablets.