DEV Community

mrcaption49
mrcaption49

Posted on • Edited on

Bulk Collect | Partitioning | Parallel Execution | Materialized Views | Dynamic SQL | Pipelined Table Functions | Large datasets

Detailed explanation of the concepts with definitions and examples for each of the techniques to handle large datasets in Oracle:

1. Bulk Collect

Definition: BULK COLLECT is a mechanism used in PL/SQL to fetch multiple rows into a PL/SQL collection (like an array or table) in a single context switch, reducing the overhead of fetching rows one by one.

Example:

DECLARE
  TYPE emp_table_type IS TABLE OF emp%ROWTYPE;
  emp_table emp_table_type;
BEGIN
  SELECT * BULK COLLECT INTO emp_table FROM emp;
END;
Enter fullscreen mode Exit fullscreen mode

Explanation: Instead of fetching one row at a time, this technique retrieves all rows from the emp table and stores them in the emp_table collection in a single fetch.

2. FORALL for Bulk DML Operations

Definition: FORALL is a PL/SQL command used to perform bulk DML (INSERT, UPDATE, DELETE) operations using a collection of data, which executes the DML statement for all elements in the collection in one operation.

Example:

DECLARE
  TYPE emp_id_type IS TABLE OF emp.empno%TYPE;
  emp_ids emp_id_type := emp_id_type(7839, 7566, 7698);
BEGIN
  FORALL i IN INDICES OF emp_ids
    UPDATE emp SET sal = sal * 1.1 WHERE empno = emp_ids(i);
END;
Enter fullscreen mode Exit fullscreen mode

Explanation: This updates the salary of employees with the specified empno values in the emp_ids collection in bulk, which is faster than running individual updates for each employee.

3. Partitioning

Definition: Partitioning is the practice of dividing a large database table into smaller, more manageable pieces called partitions, usually based on a key like date or range. This improves query performance and manageability.

Example:

CREATE TABLE sales (
  sales_id NUMBER,
  sales_date DATE,
  amount NUMBER
)
PARTITION BY RANGE (sales_date) (
  PARTITION p_2021 VALUES LESS THAN (TO_DATE('01-JAN-2022', 'DD-MON-YYYY')),
  PARTITION p_2022 VALUES LESS THAN (TO_DATE('01-JAN-2023', 'DD-MON-YYYY'))
);
Enter fullscreen mode Exit fullscreen mode

Explanation: The sales table is partitioned by the sales_date column, which helps to manage and query specific ranges of data more efficiently.

4. Parallel Execution

Definition: Parallel execution splits a large query into smaller tasks that are run concurrently on multiple CPU cores, reducing the overall query execution time.

Example:

SELECT /*+ PARALLEL(4) */ * FROM sales WHERE sales_date BETWEEN TO_DATE('01-JAN-2021', 'DD-MON-YYYY') AND TO_DATE('31-DEC-2021', 'DD-MON-YYYY');
Enter fullscreen mode Exit fullscreen mode

Explanation: The hint PARALLEL(4) tells Oracle to use 4 CPU cores to execute the query concurrently, speeding up the retrieval of data from the sales table.

5. Materialized Views

Definition: Materialized views are database objects that store the result of a query physically, and can be refreshed periodically, reducing the need to re-execute complex queries.

Example:

CREATE MATERIALIZED VIEW mv_sales_summary AS
SELECT product_id, SUM(amount) AS total_sales
FROM sales
GROUP BY product_id;
Enter fullscreen mode Exit fullscreen mode

Explanation: The mv_sales_summary materialized view stores the summarized sales data, so queries can fetch this precomputed data instead of recalculating it every time.

6. Indexes

Definition: Indexes are database objects that optimize the retrieval of rows based on specific columns, speeding up query execution times, particularly for SELECT queries.

Example:

CREATE INDEX idx_sales_date ON sales (sales_date);
Enter fullscreen mode Exit fullscreen mode

Explanation: The idx_sales_date index improves query performance when filtering by sales_date, as the database can quickly locate the relevant rows using the index.

7. Dynamic SQL

Definition: Dynamic SQL allows you to build and execute SQL statements dynamically at runtime, providing flexibility to handle varying queries that cannot be predefined.

Example:

DECLARE
  v_sql VARCHAR2(1000);
BEGIN
  v_sql := 'SELECT * FROM ' || table_name;
  EXECUTE IMMEDIATE v_sql;
END;
Enter fullscreen mode Exit fullscreen mode

Explanation: This dynamic SQL statement is constructed at runtime based on the table_name variable, allowing you to execute any query dynamically.

8. Pipelined Table Functions

Definition: A pipelined table function returns rows iteratively (one by one), allowing large result sets to be processed and returned without storing them all in memory.

Example:

CREATE OR REPLACE FUNCTION get_emp_list RETURN t_emp_list PIPELINED AS
  CURSOR c_emp IS SELECT ename FROM emp;
BEGIN
  FOR rec IN c_emp LOOP
    PIPE ROW (rec.ename);
  END LOOP;
  RETURN;
END;
Enter fullscreen mode Exit fullscreen mode

Explanation: The function get_emp_list returns employee names one row at a time using the PIPE ROW command. This allows the consumer of the function to begin processing rows before the entire result set is retrieved.

Conclusion

By using these techniques like Bulk Collect, FORALL, Partitioning, Parallel Execution, Materialized Views, Indexes, In-Memory Options, Exadata, Dynamic SQL, Pipelined Table Functions, and Bulk DML, you can significantly improve the performance of queries and DML operations on large datasets in Oracle. Each technique serves a different purpose and can be combined to achieve optimal performance for specific use cases.

Top comments (0)