SQL-Relay: An Event-Driven Rule-Based Database Gateway

Database users often submit similar queries to retrieve certain information from the database. We use user access event to represent a set of similar queries. A user access event contains an SQL template and a set of parameters, where the value of a parameter can be a constant or a variable. For example, event (“select name from customer where id =%”,101) represents a single query which retrieves the name of customer 101, while event (“select name from customer where id =%”,g cid) represents a set of queries which retrieve the name of given customer. The event execution orders are represented by using dependency graphs, which are called user access paths. In this paper, we propose an event-driven rule-based database gateway, SQLRelay. It makes use of user access patterns to improve query performance. The principle of our solution is as follows. For each frequent user access event (i.e., the frequency of the event is higher than a predefined threshold), we predefine a set of execution rules. When a query is submitted, we find the best matched event, and execute the predefined rules associated with it. There are three kinds of rules: global rewriting rules, local rewriting rules and prefetching rules. A global rewriting rule aims to rewrite the current event, e.g., make use of indices, materialized views, to get a better response time. A prefetching rule pre-fetches the answer of a query to be submitted according to the current request sequence. In some cases, semantic relationships exist between the queries of a user access path, thus a local rewriting rule can make use of such semantic relationship to rewrite the current query to answer multiple queries. For example, if we know a user will submit a query whose answer contains that of the current query, we can submit it instead of the current query to the server, and use the query result to answer both queries.