4 ms·

I'm not sure what you meant by "online rebalancer" above, but shard rebalancer in Citus is open source since March 2021: https://www.citusdata.com/blog/2021/03/

• pykello 5y ago
  Ex-Citus here. The open sourced shard rebalancer blocks writes to the shard being moved. Online rebalancer (closed source) uses logical replication and doesn't block writes to shards being moved, except for a brief period. Everything is the same except how shard moves are implemented.
  • craigkerstiens 5y ago
    Yeah, echo'ing on here to be extra clear. What is open-sourced holds a write-lock while rebalancing. So that it rebalances sure, but it's only marginally better than a dump/restore. You can still read yes, but I'm not sure of many applications that can be okay with no writes flowing to a table for hours while rebalancing is happening.
    • ablekh 5y ago
      Got it, thank you! I'm just wondering about whether this limitation can be alleviated / worked around by combining sharding and replication. In that case, I would expect the primary DB cluster to maintain the write lock during shard rebalancing, while allowing writes to replicas (upon primary cluster's rebalancing finish, the roles would reverse and rebalancing would be applied to replicas, while primary is already write lock-free).
  • ablekh 5y ago
    Understood. Thank you for the clarification.