"Query optimization is a feature of many relational database management systems and other databases such as NoSQL and graph databases."
The process of optimizing database queries to reduce execution time and improve overall performance.
Indexing: The process of creating and organizing index data structures to optimize database queries.
Query plans: A set of steps or operations that are executed by the database management system to fulfill a query.
Query optimizer: A tool that tries to generate an optimal query execution plan.
Join algorithms: Different algorithms for joining multiple tables in a database.
Cost model: A mathematical model that estimates the expected cost of query execution.
Statistics: Information about the distribution of data in a database, used by the optimizer to make better decisions.
Partitioning: Dividing large tables into smaller, more manageable parts.
Selectivity: A measure of the number of rows returned by a query compared to the total number of rows in a table.
Query rewrite: A technique that rewrites queries to obtain a more efficient execution plan.
Materialized views: Precomputed views that can speed up queries.
Caching: Storing frequently accessed data in memory to reduce disk access times.
Compression: Using algorithms to reduce the amount of data stored in a database, saving storage space and potentially improving query performance.
Denormalization: The process of adding redundant data to a database schema to improve query performance.
Refactoring: Changing the schema or design of a database to improve performance.
Profiling: Measuring query performance to identify potential bottlenecks or areas for optimization.
Execution Plan Optimization: This type of optimization involves selecting the best execution plan for a query by analyzing the query structure, the available indexes, and statistics about the data.
Cost-Based Optimization: This type of optimization is based on cost estimates for different query execution plans, and it selects the one with the lowest cost.
Index Selection Optimization: This type of optimization involves selecting the best index to use for a query, based on the query's criteria and the available indexes.
Join Order Optimization: This type of optimization involves selecting the best order in which to join tables in a query, based on the size of the tables and the availability of indexes.
Memory Management Optimization: This type of optimization involves managing the available memory to minimize page faults and optimize cache usage.
Parallelization Optimization: This type of optimization involves dividing a query into smaller parts and executing them concurrently on multiple processors or machines.
Predicate Optimization: This type of optimization involves optimizing the criteria used in a query's WHERE clause, to reduce the number of records that need to be scanned.
Projection Optimization: This type of optimization involves selecting only the columns that are required for a query's result set, to reduce the amount of data returned.
Subquery Optimization: This type of optimization involves optimizing the execution of subqueries within a larger query, to reduce their execution time.
Table Partitioning Optimization: This type of optimization involves dividing large tables into smaller, more manageable partitions, to reduce the amount of data scanned during queries.
View Optimization: This type of optimization involves optimizing queries based on views, to reduce the complexity and size of the underlying queries.
Materialized View Optimization: This type of optimization involves creating materialized views based on frequently used queries, to precompute and store the results for faster access.
Query Hint Optimization: This type of optimization involves using query hints to provide additional information to the optimizer, to improve the selection of the best execution plan.
"The query optimizer attempts to determine the most efficient way to execute a given query by considering the possible query plans."
"Generally, the query optimizer cannot be accessed directly by users."
"Once queries are submitted to the database server, and parsed by the parser, they are then passed to the query optimizer where optimization occurs."
"Some database engines allow guiding the query optimizer with hints."
"A query is a request for information from a database. It can be as simple as 'find the address of a person with Social Security number 123-45-6789...'"
"The result of a query is generated by processing the rows in a database in a way that yields the requested information."
"The purpose of query optimization, which is an automated process, is to find the way to process a given query in minimum time."
"Finding the exact optimal query plan, among all possibilities, is typically very complex, time-consuming by itself, may be too costly, and often practically impossible."
"Thus query optimization typically tries to approximate the optimum by comparing several common-sense alternatives."
"...to provide in a reasonable time a 'good enough' plan which typically does not deviate much from the best possible result." Quotes for remaining questions:
"Since database structures are complex, in most cases, and especially for not-very-simple queries, the needed data for a query can be collected from a database by accessing it in different ways, through different data-structures, and in different orders."
"Processing times of the same query may have large variance, from a fraction of a second to hours, depending on the chosen method."
"The large possible variance in time justifies performing query optimization."
"Finding the exact optimal query plan... often practically impossible."
"...by comparing several common-sense alternatives."
"The purpose of query optimization, which is an automated process..."
"Query optimization is a feature of many relational database management systems and other databases such as NoSQL and graph databases."
"A query is a request for information from a database."
"Once queries are submitted to the database server, and parsed by the parser, they are then passed to the query optimizer where optimization occurs."