Testing Concurrency in Databases still Matters

The report provides observations by re-running a suite of test cases specified to test the implementation of isolation levels by commercial database management systems and compares the results with ones obtained by earlier versions of the same systems. These particular tests focus on database systems that were traditionally known to implement single version concurrency control relying on locking. For the testing, we have used HISTEX. Among interesting observations, we can see that a commercial DBMS has increased its precision over the years for transactions running at the lower isolation levels than the stricter one due to the introduction of multiversion concurrency control. We have also discovered a discrepancy in the behavior of a database system when performing reads in different ways and unless it is addressed by the vendor we believe it needs to be considered seriously by database administrators in order to guarantee consistent behavior of the database system utilization..