Consistent synchronization schemes for workload replay

Oracle Database Replay has been recently introduced in Oracle 11g as a novel tool to test relational database systems [9]. It involves recording the workload running on the database server in a production system, and subsequently replaying it on the database server in a test system. A key feature of workload replay that enables realistic reproduction of a real workload is synchronization. It is a mechanism that enforces specific ordering on the replayed requests that comprise the workload. It affects the level of request concurrency and the consistency of the replay results when compared to the captured workload. In this paper, we define the class of consistent replay synchronization schemes and study, for the first time, the spectrum they cover and the tradeoffs they present. We place the only scheme proposed so far [9], the one implemented in Oracle 11g Release 1, within the aforementioned spectrum and show that it is coarse-grained and more restrictive than necessary, often enforcing dependencies between calls that are independent. By enforcing needless waits, it decreases the level of possible concurrency and degrades performance. To overcome these drawbacks, we identify the best scheme within the spectrum; it is finer-grained than its counterparts and strikes the right balance across different tradeoffs: it enforces a partial ordering on the replayed calls that minimizes the number of required waits and maximizes the level of concurrency, without compromising consistency of the replay results. We have implemented the new scheme in Oracle 11g Release 2. Our experiments indicate that it produces better quality replays than the pre-existing one for major classes of workload.