Parallel Commits: A New Atomic Commit Protocol for Distributed Transactions
I like the elegance and simplicity of two-phase commits. I didn't understand the criticism in the article; maybe it's something specific to CockroachDB. In my experience with two-phase commits, if the system crashes before a transaction is fully processed and committed, it should be fully reprocessed (from scratch) once the server restarts.<p>In one of my open source projects with RethinkDB (which doesn't natively support atomic transactions), I implemented a distributed 'parallel' two-phase commit mechanism by assigning each pending record a shard key (an integer derived from a hash of the record id); then worker servers would decide which subset/range of DB records to process/commit based on a hash of their own server id (which would tell them which range of shard keys/records they were responsible for). Only when a record had been fully processed, its status would be updated as committed by writing a 'settled' flag on that record.<p>Whenever a server failed and restarted, it would pick up processing from the last successful commit. If a server did not restart, the worker count would be updated and remaining workers would redistribute the partitions among themselves based on the shard keys of the records.