Minimizing aborts in an epoch based transaction protocol for deterministic databases
M.W. Schutte (TU Delft - Electrical Engineering, Mathematics and Computer Science)
Asterios Katsifodimos – Mentor (TU Delft - Web Information Systems)
Burcu Külahçıoğlu Özkan – Graduation committee member (TU Delft - Software Engineering)
K. Psarakis – Coach (TU Delft - Web Information Systems)
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Abstract
Today's need for highly available systems leads to data partitioning and replication across multiple nodes. Providing strong transactional consistency in a distributed database requires extensive communication. For this, algorithms such as two phase commit are used. These communication algorithms add extra network latency's. For application developers and database systems, this is the reason for lowering the isolation level of a database. Deterministic databases run transactions effectively without communication between replicas. Most deterministic databases need the read write sets of a transaction prior to execution to calculate a deterministic execution schedule. Aria does not need the read write sets a priory but uses an epoch based commit protocol. The commit protocol is an optimistic concurrency control algorithm that executes all transactions against a snapshot in the execution phase and determines which transactions can commit in the commit phase. For most workloads Aria outperforms state of the art deterministic databases. However, for high contention workloads Aria suffers performance because of high abort rates. To overcome this problem this thesis proposes two solutions: 1) Lowering the isolation level to snapshot isolation. 2) Reordering the input sequence of transactions on transaction degree. We have found that lowering the isolation level to snapshot isolation allows for 3\% less aborts per epoch and reduces latency from 210 ms to 170ms. Reordering the transaction sequence allows for 5 percent less aborts per epoch for snapshot isolation and serializable isolation level. Reordering transactions on degree for serializable isolation level reduces the average latency from 210 ms to 150 ms. Snapshot isolation reordering transactions on degree reduces the average latency from 170 ms to 120 ms.