Correctness of table GC in asynchronous networks #151

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opened 2021-11-08 15:18:46 +00:00 by lx · 0 comments

lx commented

2021-11-08 15:18:46 +00:00

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PR #135 mostly fixes the CRDT-GC issue by implementing a 24-hour delay before anything is garbage collected in a table. This works under the assumption that rebalances that follow data shuffling terminate in less than 24 hours.

However, in distributed systems, it is generally considered a bad practice to make assumptions that information propagates in a certain time interval: this consists in making a synchrony assumption, meaning that we are basically assuming a computing model that has much stronger properties than otherwise. To maximize the applicability of Garage, we would like to remove this assumption, and implement a system where time does not play a role. To do this, we would need to find a way to safely disable the GC when data is being shuffled around, and safely detect that the shuffling has terminated and thus the GC can be resumed. This introduces some complexity to the protocol and hasn't been tackled yet.

**PR #135 mostly fixes the CRDT-GC issue** by implementing a 24-hour delay before anything is garbage collected in a table. This works under the assumption that rebalances that follow data shuffling terminate in less than 24 hours. **However**, in distributed systems, it is generally considered a bad practice to make assumptions that information propagates in a certain time interval: this consists in making a synchrony assumption, meaning that we are basically assuming a computing model that has much stronger properties than otherwise. To maximize the applicability of Garage, we would like to remove this assumption, and implement a system where time does not play a role. To do this, we would need to find a way to safely disable the GC when data is being shuffled around, and safely detect that the shuffling has terminated and thus the GC can be resumed. This introduces some complexity to the protocol and hasn't been tackled yet.