What is query optimization?
Query optimization is the process of selecting the most efficient query plan for executing a given query in order to minimize resource usage and improve response time. It involves exploring alternative query plans and selecting the one with the lowest cost based on database statistics, query predicates, and system parameters.
The database optimizer analyzes queries and makes enhancements like reordering joins, pushing down predicates, choosing optimal join types and access paths. Advanced optimizers like the Apache DataFusion optimizer even optimize across queries.
Optimizers consider possible plan permutations and estimate their costs using statistics on data size, distribution, indexes, and hardware capabilities. The optimal plan balancing all tradeoffs is chosen and passed to the execution framework.
Optimizers also perform tasks like in-memory processing, code generation, memory management, and leveraging user defined functions. Optimization is key for performant query execution.
How does query optimization work?
Query optimizers use rules and cost models to build, compare and evaluate different query execution plans to find the optimal one. Common optimizations include join reordering, pushing down filters, switching access paths, plan caching and more based on cost estimates.
Advanced optimizers leverage techniques like dynamic programming, recursive rewriting, materialized views and histogram analytics to improve plan choices.
Why is query optimization useful? Where is it applied?
Query optimization is essential for efficient database system performance. It provides huge cost savings compared to naive query plans on complex workloads. Database management systems like Oracle, SQL Server, Postgres all employ advanced optimizers andtuning techniques to minimize expensive disk I/O, network usage and computational resources.
FAQ
What are the main techniques used in query optimization?
Common optimization techniques include:
What are challenges faced in query optimization?
Challenges include:
How can query performance be improved manually?
Some manual query tuning approaches include:
What future innovations may shape query optimization?
References:
Related Topics
Memory Management
Memory management refers to the allocation, deallocation and organization of computer memory resources for running programs and processes efficiently.
Execution Framework
An execution framework is a distributed system that automates and manages aspects like resource allocation, scheduling, fault tolerance and execution of large-scale computational jobs.
User Defined Functions (UDF)
A user-defined function (UDF) is a programming construct that allows developers to create custom functions in a database, query language or programming framework to extend built-in functionality.
Inner Joins
An inner join is a type of join operation used in relational databases to combine rows from two tables based on a common column between them.
Outer Joins
An outer join returns all rows from one or both tables in a join operation, including those without matching rows in the other table. It preserves rows even when no related matches exist.