Transaction chopping

Abstract

Chopping transactions into pieces is good for performance but may lead to nonserializable executions. Many researchers have reacted to this fact by either inventing new concurrency-control mechanisms, weakening serializability, or both. We adopt a different approach. We assume a user who —has access only to user-level tools such as (1) choosing isolation degrees 1ndash;4, (2) the ability to execute a portion of a transaction using multiversion read consistency, and (3) the ability to reorder the instructions in transaction programs; and —knows the set of transactions that may run during a certain interval (users are likely to have such knowledge for on-line or real-time transactional applications). Given this information, our algorithm finds the finest chopping of a set of transactions TranSet with the following property: If the pieces of the chopping execute serializably, then TranSet executes serializably . This permits users to obtain more concurrency while preserving correctness. Besides obtaining more intertransaction concurrency, chopping transactions in this way can enhance intratransaction parallelism. The algorithm is inexpensive, running in O(n×(e+m)) time, once conflicts are identified, using a naive implementation, where n is the number of concurrent transactions in the interval, e is the number of edges in the conflict graph among the transactions, and m is the maximum number of accesses of any transaction. This makes it feasible to add as a tuning knob to real systems.

Database Replication Using Generalized Snapshot Isolation

“…Atluri et al [4] have studied the serializability of weaker isolation levels such as the ANSI SQL isolation levels for centralized databases. Shasha et al [28] have presented the conditions that allow a transaction to be divided into smaller sub-transactions that release locks earlier than the original transaction under traditional locking policies. Kemme et al [21] have discussed how to implement different isolation levels (including serializability) in replicated databases using group communication primitives.…”

Efficient Processing of Client Transactions in Real-Time

“…We term this concept of splitting transactions as transaction decomposition. This is conceptually different from transaction chopping as proposed in [44]. The primary objective in transaction chopping is to reduce locking delays in a transaction processing environment.…”

Transaction Chopping for Parallel Snapshot Isolation

“…Recent years have seen a plethora of consistency model proposals that make different trade-offs between consistency and performance [6,7,20,22]. Unfortunately, whereas transactional consistency models have been well-studied in the settings of smaller-scale databases [2,13,21] and transactional memory [5,12,14,16], models for large-scale distributed databases are poorly understood. In particular, we currently lack a rich theory that would guide programmers in using such models correctly and efficiently.…”

“…In this paper we make a step towards building such a theory by investigating the classical problem of transaction chopping [21] for a promising consistency model of parallel snapshot isolation (PSI) [22]. PSI weakens the classical snapshot isolation (SI) [8] in a way that allows more efficient large-scale implementations.…”

“…A common guideline for programmers using relational databases and transactional memory is to keep transactions as short as possible to maximise performance; long transactions should be chopped into smaller pieces [3,21,24]. This advice is also applicable to PSI databases: the longer a transaction, the higher the chances that it will abort due to a write conflict.…”