In a doubly linked list, each node contains references to the next node and the previous node. This is because each node has two pointers, one pointing to the next node and one to the previous node.

A database system ensures durability, one of the ACID properties, by using techniques like Write-Ahead Logging (WAL). In WAL, before modifying data in the database, the system first writes the changes to a log file on disk. This log file acts as a record of all transactions, and in the event of a system failure, the database can recover by replaying the logged transactions from the log file to restore the database to a consistent state. This ensures that even if the system crashes, committed transactions are not lost and the database remains durable. Other techniques such as checkpoints and transaction logs also contribute to ensuring durability in database systems, making them robust against failures.

In a priority queue, elements are dequeued based on their priority level, where higher-priority elements are dequeued before lower-priority elements. Priority queues are often implemented using heaps to efficiently maintain the highest priority element at the front.

Optimizing a slow SQL query on a large dataset involves using proper indexing techniques. Indexes help the database system locate and retrieve data more efficiently, leading to faster query execution. Rewriting the query using optimized SQL syntax can also improve performance. Increasing server RAM or adding more data won't directly optimize the query's speed.

The CSS box model describes the structure of an HTML element by breaking it down into four components: content, padding, border, and margin. Content refers to the actual content within the element, while padding adds space between the content and the border. The border outlines the content and padding, and margin provides space outside the border. Understanding the box model is essential for layout design and spacing in CSS.

Security challenges in containerization include isolation breaches and vulnerabilities such as kernel exploits. Mitigation involves using secure container images, implementing strict network policies, and regularly updating containers and underlying systems.

Flexbox and Grid are two layout models in CSS used for designing web layouts. Flexbox is a one-dimensional layout method for laying out items in rows or columns, while Grid is a two-dimensional layout method for complex layouts.

Journaling in a file system involves recording changes to data in a journal before actually writing them to the main storage. This technique enhances reliability by preventing data loss in case of unexpected system crashes or power failures. When a system crashes, the journal can be used to replay transactions that were not yet committed to the main storage, ensuring data consistency and integrity. As a result, journaling helps maintain the reliability and consistency of file systems, making them more resilient to failures and ensuring data integrity.

The SELECT DISTINCT keyword is used in SQL to retrieve only unique values from a specified column in a table. When you use SELECT DISTINCT, the query results will eliminate duplicate values, presenting only distinct values in the result set. This is particularly useful when you want to analyze or display unique entries without redundancy. It's important to note that SELECT DISTINCT operates on a single column or a combination of columns, and it can be combined with other clauses like WHERE for more specific filtering. Understanding how to use SELECT DISTINCT helps in generating accurate and concise reports or data analysis results.

The correct option is Planning. The first phase in the SDLC is Planning, where project goals, scope, requirements, and resources are defined.