SQL Server Internals Explained: An Introductory Guide

Understanding SQL Server's internal architecture and components, such as the Relational Engine, Storage Engine, indexes, and locking mechanisms, helps database administrators (DBAs) and developers optimise performance, troubleshoot issues, and ensure efficient data management. Each part of SQL Server, from how data is stored to how queries are processed, contributes to its overall efficiency and scalability. By diving deeper into SQL Server internals, one can make informed decisions to improve database performance and stability.

Here’s an overview of some of the key internal components and concepts of SQL Server:

Some common reasons why the transaction log cannot be reused automatically

Managing SQL Server databases may sometimes be challenging especially when it comes to dealing with transaction log file internal space usage. More specifically, today I am going to talk about SQL Server wait types that may prevent SQL Server from automatically reusing transaction log internal space and therefore resulting in running out of space and affecting detrimentally on the availability of the database. For instance, if the recovery model of the database is either Full or Bulk-Logged then you may see a LOG_BACKUP wait type while the next backup log is waited to be run. Consequently, if those databases do not have Log Backups tasks, their transaction log files will be growing without control and when they take all the disk space available the databases will stop working until the internal space of the transaction logs is truncated by executing log backups manually.

Boosting SQL Server Efficiency: Why You Should Update Statistics Manually

While SQL Server provides automatic statistics management, manually updating statistics allows for greater control over database performance. Regularly monitoring the state of your statistics and updating them as necessary can lead to more efficient query execution, especially in environments with dynamic data and high transaction volumes. By implementing a proactive strategy for managing statistics—whether through scheduled jobs, maintenance plans, or manual updates—you can ensure that your SQL Server instance continues to perform optimally over time.

Detailed Explanation of SQL Server Query Hints

SQL Server query hints are directives that can be included in your SQL queries to guide the SQL Server Query Optimiser in executing them. Typically, SQL Server automatically selects the most efficient execution plan based on the query and underlying data. However, query hints enable you to override the optimiser’s default choices, giving you greater control over specific aspects of query execution. 

While these hints can significantly enhance performance in particular scenarios, they must be used cautiously and strategically. Incorrect application of hints can lead to degraded performance or unpredictable outcomes. Therefore, it is essential to thoroughly test your queries both with and without hints to evaluate their impact. Ensure that hints are employed appropriately and suited to your specific workloads to achieve optimal results.

Below is a detailed look at common SQL Server query hints, examples of their usage, and the potential risks associated with each.

Understanding the SQL Server Query Optimiser: A Comprehensive Overview

The SQL Server Query Optimiser is a crucial component of Microsoft SQL Server, responsible for determining the most efficient way to execute a given query. The optimiser takes into consideration various factors, including the structure of the query, available indexes, statistics about the data, and the overall database schema. Here is a detailed breakdown of its functionalities, processes, and related concepts. 

1. Purpose of the Query Optimiser

The primary goals of the Query Optimiser include:

• Generating Execution Plans: The optimiser creates a roadmap that describes how SQL Server will access the data required by the query.
• Maximising Efficiency: By evaluating different potential execution paths, the optimiser selects the one that minimises resource utilisation, such as CPU, memory, and disk I/O.
• Improving Response Times: A well-optimised query results in faster execution, contributing to better overall system performance.

Detecting Poor Cursor Usage in SQL Server

Undoubtedly, poor cursor usage is a critical issue to review in order to mitigate the risk of CPU bottlenecks and to assess whether cursors are the most appropriate means for processing or if set-based operations would be more effective. It is well known that set-based operations are generally more efficient; however, if you choose to use cursors, you must ensure that they do not adversely affect the performance of the database.

Looking deeper into the physical & logical architecture - Transaction Log File

Beyond all doubt, it is essential to have a good understanding of the Transaction Log (T-Log) so that we can diagnose unforeseen performance issues related to it and I am sure that almost everyone had at least one. The T-Log is basically a record of all transactions happening to the database. All these transactions are actually first written to the physical T-Log file, and then after a CHECKPOINT, is written to the Data File via the Lazy Writer process. Some of the uses of T-Log are: as a point in time recovery (full recovery model), to record the Start and End of each transaction, every data modification (insert, update, delete) including system SP's, DDL statements to any table including system tables, every extent and page allocation and de-allocation operation, and creation or drop of tables and indexes.

Getting Important Information of SQL Server Backups

Regardless of the method employed to take SQL Server backups, they must be carefully monitored around the clock, particularly in critical database environments where data changes rapidly. Keeping backups current is vital, as they can save considerable time when it comes to recovering databases in the event of unforeseen incidents. Furthermore, it has been disappointing to observe numerous environments lacking a backup strategy, often with no one designated to oversee them. In this context, it is evident that these businesses were at significant risk of losing vast amounts of data and incurring substantial financial losses.

Sometimes, there is a belief that backing up the entire virtual machine is sufficient; however, this type of backup serves a different purpose than a dedicated database backup. Consequently, SQL Server database backups cannot be substituted with virtual machine backups, which can be time-consuming, inadequate, and impractical for databases. Thus, implementing an appropriate database backup strategy (for example, with Full + Differential + Log Backups) and closely monitoring them are essential tasks for ensuring the recovery process of databases.