On Thu, Oct 15, 2015 at 12:00 AM, Semyon Boikov <[email protected]> wrote:
It seems there is better approach to resolve these conflicts to do not fail > all conflicting transactions: > - we should order all transactions by some attribute (e.g. all transactions > already have unique version) > - transaction with greater order should always 'win' transaction with lower > order > - per-entry queue with waiting transactions should be sorted by this order > - when transaction tries to acquire entry lock it is added in waiting queue > if queue is empty or last waiting transaction have lower order, otherwise > transaction fails > > With this approach transaction lock assignment is ordered and transactions > with lower order never wait for transactions with greater order, so this > algorithm should not cause deadlocks. > > I also created unit test simulating this algorithm and it did not reveal > any issues. Also in this unit tests I measured percent of rollbacks when > concurrent updates have lots of conflicts: with 'try-lock' approach percent > of rollbacks is ~80%, with new algorithm is ~1% (but of course with > real-life test results can be different). > The success ratio with ordered approach is naturally going to be better. However, I think the performance will suffer, because queues are generally expensive. Have you tried comparing performance of the queue-based approach vs. the try-lock one?
