The invention provides a query optimization algorithm in the technical field of database, and is mainly used for solving the problem of distributed database multi-join query optimization. The technical scheme adopted by the invention is as follows: 1. pre-optimizing over-ternary relation join, ...
Use the LIMIT clause to restrict the number of rows the query returns. This can significantly boost MySQL performance, especially for queries with large result sets. Reducing query execution time can be achieved by implementing various optimization techniques, such as indexing strategies and caching me...
除了通过动态规划剪枝之外,当连接表过多时,会选择一些局部最优解的方式: greedy join enumeration algorithm 在每次循环中,选择使总代价最低的方案 多项式时间算法,但结果不一定最优 Randomized algorithm 随机重写查询方案,利用模拟退火等算法进行优化 Genetic algorithm(遗传算法) 通过连接方案(结合子代)和随机突变进行优...
public Map<Set<String>, QueryOperator> minCostJoins( Map<Set<String>, QueryOperator> prevMap, Map<Set<String>, QueryOperator> pass1Map) { Map<Set<String>, QueryOperator> result = new HashMap<>(); // pass1Map存储的是一张单一的表和它的遍历方式 // 遍历已经做过join操作的表,即左深树...
Database | 浅谈Query Optimization (1) 综述 由于SQL是声明式语言(declarative),用户只告诉了DBMS想要获取什么,但没有指出如何计算。因此,DBMS需要将SQL语句转换成可执行的查询计划(Query Plan)。但是对同样的数据可以有多种查询方案,性能也差距很大,查询优化器(Query Optimizer)的任务就是从给定的查询中选择一个最...
这一步的输出是一个逻辑查询树,查询的代数表示形式为逻辑关系运算符的树(例如,Select,Join等)。例如,图1.1显示了在解析和验证步骤之后查询1的输出逻辑查询树。 图1.1 Query optimization: 查询优化器将逻辑查询树作为输入,并负责生成由执行引擎解释或编译的高效执行计划。执行计划(也称为计划)是物理操作符的树,其...
Currently, the optimizer uses a standard algorithm to estimate the selectivity of selection and join predicates. However, the algorithm does not always work well in cases in which predicates contain functions or type methods. In addition, predicates can contain user-defined operators about which the...
This paper presents hash join optimization based on shared cache CMP (chip multi-processor). Firstly, it proposes a multithreaded execution framework of hash join based on Radix-Join algorithm, and then analyzes the factors which affect the performance of multithreaded Radix-Join algorithm through two...
This paper briefly describes the target of the distributed query optimization,elaborates the basic idea and implementation process of the semi-join optimization algorithm,and analyzes the advantages and disadvantages.In order to improve the algorithm,this paper puts forward the idea of PERF join algorit...
cache多核处理器Hash连接优化 Hash Join Query Optimization Based on Shared-Cache Chip Multi-ProcessorDeng, YaDanJing, NingXiong, Wei