[lifepillar]

I see that MVCC is still your preferred way of doing CC, and what academic research is mostly focused. I am wondering whether that’s an advantage for in-memory databases specifically.

I was once discussing MVCC vs 2PL with an experienced Sybase and SQL Server guy, and he claimed that, when transactions are implemented properly and the database is well-designed (no surrogate keys, in particular), 2PL leads to better performance and no deadlocks, while “readers do not block writers” leads to lots of aborted transactions in a heavy OLTP workload. I verified that (I should still have the code around): lots of conflicts in PostgreSQL vs smooth concurrent execution with no retries in Sybase and SQL Server.

I have since heard similar opinions from other SQL Server practitioners: they disable MVCC and rely only on good ol’ 2PL.

[apavlo]

See our 2014 paper on evaluating CC protocols on in-memory system with high contention / core counts:

https://www.vldb.org/pvldb/vol8/p209-yu.pdf

All the protocols regress to the same. This evaluation was only with stored procedures though. It would be worth doing a similar investigation with conversational DB protocols (e.g., JDBC, ODBC).

[sundar28]

Thanks for the reminder.. this was a great paper, and I'm curious - why would conversational protocols indicate any difference? Also - curious if any such tests have used libraries such as seastar?