Parsing
1. What is SQL parsing and why is it important?
SQL parsing is the process of analysing and validating an SQL statement to ensure it is syntactically correct and creating an execution plan for the statement.
2. What is Hard Parsing?
Hard Parsing occurs when the database fully parses an SQL statement from scratch, typically on the first execution or when there are significant changes to the statement. It's resource-intensive and can be slow.
3. What is Soft Parsing?
Soft Parsing occurs when the database reuses an existing execution plan for a similar SQL statement, often with different bind variables. It is faster and more efficient. Soft parsing is used to reduce the overhead of hard parsing and improve performance.
4. Explain the steps involved in SQL parsing. What happens during each step, and why is each step necessary?
The steps include lexical analysis (tokenization), syntax check, semantic analysis, query parsing, execution plan generation, optimization, and execution. Each step is necessary to ensure the SQL statement is valid, secure, and optimised for efficient execution.
5. What are bind variables in SQL statements, and why are they important for reducing hard parses?
Bind variables are placeholders in SQL statements that can be dynamically replaced with specific values at runtime. They are important for reducing hard parses because using bind variables allows the database to reuse execution plans for similar statements with different values, reducing the need for full parsing and optimization.
6. What is an execution plan, and how is it generated during the parsing process?
An execution plan is a detailed outline of how Oracle will execute an SQL statement. It specifies the operations, access methods, and order of execution for retrieving data. The execution plan is generated during the parsing process based on the query parse tree and query optimization.
7. How does Oracle's query optimizer contribute to SQL parsing and execution plan generation?
Oracle's query optimizer plays a key role in generating the execution plan. It analyzes available statistics, system settings, and query complexity to determine the most efficient way to execute a query. The optimizer is responsible for choosing the optimal access paths and join methods used in the execution plan.
8. What are the common methods to reduce hard parsing in Oracle Database?
Common methods to reduce hard parsing include using bind variables, optimizing SQL statements, implementing connection pooling, and configuring shared pool settings. Caching frequently executed SQL statements and reusing execution plans also help reduce hard parses.
9. Explain the impact of hard parsing on database performance and resource utilization. How can it be measured and monitored?
Hard parsing can consume CPU and memory resources and slow down query execution. It can be measured and monitored using Oracle database performance views and tools like AWR (Automatic Workload Repository) and ASH (Active Session History) to identify high parsing-related resource consumption.
10. Can you provide an example of a situation where using bind variables significantly improved query performance by reducing hard parses?
Suppose you have a web application where users can search for products by various criteria. By using bind variables in the SQL statement, you can reuse the same execution plan for different searches, significantly improving query performance and reducing the load on the database.
