1. Indexing:
Indexing involves the creation of data structures known as indexes, which enhance query performance by enabling swift data retrieval. These indexes establish organized structures, aiding the database engine in promptly identifying rows that meet specified conditions in a WHERE clause. Although indexes boost the speed of SELECT queries, they might impede write operations. Thus, achieving a balance between read and write performance is essential when employing indexes.

CREATE INDEX idx_CustomerId ON Customer(CustomerId);

2. Composite Indexes:
Composite indexes encompass multiple columns and prove advantageous for queries that filter or sort data based on multiple criteria. This diminishes the necessity for individual indexes on each column and enhances the effectiveness of the query planner.
Let's consider a hypothetical database table called "Employees" with columns such as "First Name," "Last Name," "Department," and "Salary."

Suppose you frequently run queries that involve filtering or sorting based on both the "Department" and "Salary" columns. Creating a composite index on these two columns together could significantly improve query performance.

Here's an example of creating a composite index:

CREATE INDEX idx_Department_Salary ON Employees (Department, Salary);

3. Normalization and Denormalization:
Normalization and denormalization are two opposing database design techniques used to organize data in relational databases efficiently.

Normalization:
Normalization is the process of structuring a database to minimize redundancy and dependency by organizing tables and columns. The goal is to reduce data duplication and maintain data integrity by breaking down larger tables into smaller, related tables. Normalization typically involves decomposing larger tables into smaller ones, each containing specific types of data to avoid data redundancy and anomalies.

There are several normal forms (e.g., 1NF, 2NF, 3NF, BCNF, 4NF, 5NF) that define specific rules for organizing data to achieve normalization. The higher the normal form, the more strictly the data is organized to eliminate redundancies and dependencies.

Example of Normalization:
Consider a database for a library. Instead of having a single table with all book-related information (e.g., title, author, publisher, ISBN, genre), normalization might involve breaking this data into multiple tables:

A "Books" table containing information such as book ID, title, ISBN, and publisher.
An "Authors" table containing author ID, name, and other author-related details.
A "Book-Author" table linking books to their respective authors using their IDs.
This approach minimizes data redundancy by separating distinct pieces of information into their respective tables and using relationships to connect related data.

Denormalization:
Denormalization, on the other hand, is the process of intentionally introducing redundancy into a database to improve query performance by reducing the number of joins needed to retrieve data. It involves combining tables or adding redundant data back into normalized tables, making data retrieval faster but potentially sacrificing some normalization benefits.

Example of Denormalization:
Using the library database example, a denormalization technique might involve reintroducing redundant data into a table. For instance, if there's a frequent need to display the author's name alongside the book details, instead of always joining the "Books" table with the "Authors" table, you might include the author's name directly in the "Books" table, thus denormalizing the schema.

While this denormalized structure might improve query performance by eliminating some joins, it increases data redundancy and can lead to anomalies when updating or deleting data.

In summary, normalization focuses on minimizing redundancy and maintaining data integrity, while denormalization aims to improve performance by introducing controlled redundancy at the expense of some normalization principles. Both techniques have their advantages and trade-offs, and the choice between them depends on the specific requirements and performance considerations of the application.

4. Partitioning
Partitioning tables entails the segmentation of extensive tables into smaller, more manageable segments. This approach substantially enhances query performance as it enables the database engine to operate on reduced portions of data, thereby expediting query execution.

Example SQL code snippet for partitioning a table:

CREATE TABLE SalesData (
    SalesDate DATE,
    ProductID INT,
    Amount DECIMAL(10, 2)
) PARTITION BY RANGE (YEAR(SalesDate)) (
    PARTITION p0 VALUES LESS THAN (2020),
    PARTITION p1 VALUES LESS THAN (2021),
    PARTITION p2 VALUES LESS THAN (2022),
    PARTITION p3 VALUES LESS THAN (2023),
    PARTITION p4 VALUES LESS THAN MAXVALUE
);

5. Connection Pooling:
Utilize Connection Pooling: Employ reusing existing database connections to circumvent the overhead involved in establishing new connections for each request. This technique assists in efficiently managing and reusing database connections.

Example:

Maximizing Connection Pooling: Employing a connection pool manager like "HikariCP" in Java applications ensures the efficient handling and reuse of established database connections. This practice minimizes the overhead incurred in establishing new connections for every request, enhancing overall application performance.

6. Monitoring and Profiling:
Continuous Monitoring: Integrate monitoring tools to consistently observe the performance of the database over an extended period. Consistently track essential metrics like CPU utilization, memory allocation, and query execution durations to promptly detect and address potential concerns.

Query Profiling: Assess and examine individual query performance to identify areas of bottleneck. Utilize tools such as the MySQL Performance Schema to gain comprehensive insights into query execution.