SQL Server by Harsh Kumar

Accelerated Database Recovery (ADR) is one of the most transformative features in recent SQL Server releases, and with SQL Server 2025, it’s more powerful and flexible than ever. ADR is a SQL Server feature designed to drastically improve database availability by reengineering the recovery process. Traditional recovery could take a long time, especially with long-running transactions, because SQL Server had to scan the transaction log from the oldest uncommitted transaction. ADR changes this by introducing a new architecture that makes recovery and rollback nearly instantaneous, regardless of transaction length or database activity. Key Benefits : Fast and consistent recovery : Recovery time is no longer affected by the number or size of active transactions. Instantaneous rollback : Even very long-running transactions can be rolled back instantly. Aggressive log truncation : The transaction log is truncated more aggressively, preventing log growth even with active long transactions. H...

Standard Developer and Enterprise Developer edition in SQL Server 2025 In SQL Server 2025, two new Developer editions are introduced: Standard Developer and Enterprise Developer. These editions are designed for development and testing purposes and are licensed for free. The Standard Developer edition includes all the features of the Standard edition, while the Enterprise Developer edition offers the complete functionality of the Enterprise edition.  Standard Developer Edition Free licensing: It can be used without incurring any licensing costs.  Matches Standard edition: It mirrors the features and capabilities of the SQL Server Standard edition.  Ideal for teams: It's particularly valuable for teams whose production workloads run on Standard edition.  Narrowing the gap: It helps to minimize the difference between development and production environments, especially for applications that rely on Standard or Web/Express editions.  Improves code predictability: It ...

 Copilot Feature in SQL Server 2025: A Game-Changer for Database Management As organizations continue to embrace digital transformation, the demand for smarter, more efficient database management tools is growing. Enter SQL Server 2025, Microsoft's latest iteration of its flagship database system, which introduces a revolutionary feature—Copilot. Powered by advanced AI capabilities, Copilot is set to redefine how database administrators (DBAs) and developers interact with SQL Server. What is Copilot in SQL Server 2025? Copilot is an AI-powered assistant integrated into SQL Server 2025. Designed to augment productivity, it leverages natural language processing (NLP) and machine learning (ML) to assist users in managing databases, writing queries, optimizing performance, and ensuring data security. Built on Microsoft's Azure OpenAI service, Copilot brings intelligence directly into the SQL Server ecosystem. Key Features of Copilot Natural Language Querying : Users can write quer...

Microsoft on 19 Nov 2024 has officially announced SQL Server 2025, a revolutionary update that positions itself as an AI-ready, enterprise-grade database built to address the growing needs of modern data and AI-driven applications. Here's an overview of what makes this release groundbreaking for developers, data professionals, and businesses. Key Features and Enhancements-  AI Built-In Native Vector Indexing: Enables hybrid searches that combine structured SQL data with vector-based queries, crucial for modern AI models. Integration with AI Frameworks: Seamless support for LangChain, Semantic Kernel, and Entity Framework Core facilitates advanced AI application development. RAG (Retrieval-Augmented Generation): Built-in tools make it easier to incorporate advanced AI into applications using T-SQL. Performance and Reliability Enhanced Query Optimization and batch mode processing improve performance for analytical workloads. Optimized locking mechanisms reduce contention in high-conc...

When upgrading the operating system (OS) in a Windows cluster, there are a few methods you can consider. The appropriate method depends on the specific requirements, cluster configuration, and the available resources. Here are some common approaches: In-place upgrade : This method involves directly upgrading the existing OS on each node of the cluster. It can be suitable when the cluster nodes are capable of supporting the target OS version and when preserving applications, data, and configurations is a priority. To perform an in-place upgrade, follow the official documentation from Microsoft, which provides detailed instructions and considerations for each specific Windows version. Rolling upgrade : Similar to the rolling upgrade method described earlier, you can perform a rolling upgrade of the Windows cluster. In this case, you upgrade the OS on one node at a time while the other nodes continue to operate. By sequentially upgrading the nodes, you can maintain service availability th...

The "Rolling Upgrade" method is a commonly used approach for upgrading a cluster while minimizing downtime and maintaining service availability. It involves sequentially upgrading individual nodes or components of a cluster, one at a time, while the rest of the cluster continues to operate. Here's an overview of the steps involved in a Rolling Upgrade: Plan the upgrade : Determine the scope and requirements of the upgrade, including the target version or configuration changes. Consider factors like compatibility, dependencies, and any potential impact on applications or services running on the cluster. Prepare the upgrade : Ensure you have a backup or snapshot of the cluster's current state in case you need to roll back. Review documentation and release notes for the new version or configuration changes. Prepare any necessary upgrade scripts or tools. Start with a node or component: Select an initial node or component for the upgrade. This could be a single machine, a...

WAIT TYPES refer to the specific events or conditions that cause a query or transaction to wait for a resource to become available. Understanding wait types is essential for troubleshooting and optimizing SQL Server performance. SQL Server wait types can be broadly categorized into two group s: External waits : These waits occur when SQL Server is waiting for an external resource, such as I/O operations or network requests. Examples of external wait types include PAGEIOLATCH_EX, NETWORK_IO, and ASYNC_NETWORK_IO. DMVs related to External Waits : sys.dm_io_virtual_file_stats : This DMV provides information on I/O statistics at the file level. It can be used to identify which database files are experiencing high I/O activity. sys.dm_exec_requests : This DMV provides information on currently executing queries, including the wait type, wait time, and resource utilization. Internal waits : These waits occur when SQL Server is waiting for an internal resource, such as a latch or a lock. Exam...

Split Brain is a term used in SQL Server clustering to describe a scenario where the nodes in the cluster lose communication with each other, and each node believes that it is the only active node in the cluster. This can cause multiple issues, including data corruption, duplicate transactions, and other unexpected behaviors. Here's an in-depth detail of split brain in SQL Server clustering with examples: In a SQL Server clustering environment, there are multiple nodes that are connected to each other via a network. Each node has access to the same shared storage, which contains the SQL Server database files. In a normal situation, the nodes communicate with each other to ensure that only one node is active at any given time. This is achieved through a mechanism called a cluster heartbeat, where the nodes send signals to each other to indicate that they are still alive and functioning. However, in certain scenarios, the cluster heartbeat may fail, and the nodes may lose communicat...

A Service Principal Name (SPN) is a unique identifier for a service instance in a Windows environment. In SQL Server, SPNs are used to specify the identity under which a particular SQL Server service runs, which is necessary for Kerberos authentication and delegation in a Windows Active Directory environment. Here is a detailed explanation of SPNs in SQL Server 1. What is an SPN? An SPN is a unique name that identifies a service instance running on a computer. It is used by Kerberos authentication to associate a service instance with a service account. An SPN is made up of the service class, hostname, and port number (if applicable) that the service is running on. 2. Why are SPNs important in SQL Server? In SQL Server, SPNs are important because they are used to enable Kerberos authentication, which provides a more secure and efficient method for authenticating users than NTLM authentication. Kerberos authentication allows users to authenticate once and then reuse their credentials ...

Having thousands of databases on a single SQL Server instance can lead to several problems, including: Resource contention : Each database requires its own set of resources, such as memory, disk I/O, and CPU time. With thousands of databases, these resources can quickly become scarce and lead to performance problems. Maintenance challenges : Maintaining thousands of databases can be a daunting task, especially when it comes to tasks such as backups, restores, and monitoring. It can be difficult to keep track of which databases need maintenance and ensuring that all databases are properly maintained can become an overwhelming task. Security risks : With thousands of databases, it can be challenging to maintain proper security protocols. Each database may have its own set of users and permissions, making it difficult to manage access and enforce security policies across all databases. Increased risk of downtime : If one database experiences issues, it can potentially affect other databas...

Physical memory , also known as RAM (Random Access Memory), is a type of computer memory that is used to temporarily store data and instructions that the CPU (Central Processing Unit) needs to access quickly. Virtual memory, on the other hand, is a technique that allows the operating system to use a portion of the hard disk as if it were RAM. In SQL Server, physical memory is used to cache data and instructions that are frequently accessed by the server. This is known as the buffer pool, and it is used to improve the performance of the database by reducing the number of disk reads that need to be performed. When SQL Server needs to access data that is not in the buffer pool, it must retrieve it from disk, which can be slower than accessing it from memory. Virtual memory is used by SQL Server as a backup when the physical memory is not sufficient to store all the data and instructions that are needed by the server. In this case, the operating system will move some of the data and instr...

Memory is a critical component that can significantly impact the performance of SQL Server. When SQL Server processes data, it stores and retrieves information from memory, and the amount of memory available to SQL Server can directly affect its performance.  Buffer Cache Hit Ratio : The Buffer Cache Hit Ratio is a critical performance metric for SQL Server, which represents the percentage of data pages that are found in memory. A high buffer cache hit ratio indicates that the SQL Server is finding the data it needs in memory, which leads to faster query execution times. A low buffer cache hit ratio means that the SQL Server is having to fetch data from disk, which is slower and can lead to poor performance. For example , let's say that a SQL Server has 32 GB of memory, and the buffer cache hit ratio is 99%. This means that 99% of the data that SQL Server needs is in memory, and only 1% of the data needs to be fetched from disk. This results in faster query execution times and impr...

I/O (Input/Output) can have a significant impact on SQL Server performance as it involves the read and write operations to and from disk. Here are some factors that can impact SQL Server I/O performance: Storage Type : The type of storage you use for SQL Server can impact performance. Solid State Drives (SSDs) offer faster I/O compared to Hard Disk Drives (HDDs), but they can be more expensive. RAID Configuration : A Redundant Array of Inexpensive Disks (RAID) configuration can improve performance and provide redundancy for data protection. RAID configurations can improve read and write performance by striping data across multiple disks. Disk Layout : The way that data is laid out on disks can impact I/O performance. Using multiple disks for data, logs, and backups can help to avoid contention and improve performance. Indexing Strategy : Indexing can impact I/O performance by affecting the amount of data that needs to be read from disk. A well-designed indexing strategy can reduce the ...

The number of CPU cores can have a significant impact on the performance of SQL Server. Here is a explanation of how the number of CPU cores affects SQL Server performance, along with examples: Parallel query processing : SQL Server can take advantage of multiple CPU cores to process queries in parallel, which can result in faster query processing times.  For example , suppose you have a query that takes 10 seconds to run on a system with 4 CPU cores. If you double the number of CPU cores to 8, the same query may only take 5 seconds to run, assuming the system has enough memory and disk I/O capacity to handle the increased workload. Concurrent user activity : SQL Server can handle more concurrent user activity with more CPU cores. Each user connection can be assigned to a separate CPU core, which can result in more efficient processing of queries and requests.  For example , suppose you have a system with 4 CPU cores and 50 users accessing SQL Server simultaneously. If each us...

Prefetching is a technique used by SQL Server to improve query performance by anticipating the data that will be needed for a query and reading it into memory in advance. This reduces the number of I/O operations required to fetch data from disk, which can significantly improve query performance. There are several mechanisms that SQL Server uses for prefetching, including: Read-Ahead : This mechanism anticipates the data pages that will be needed for a query and reads them from disk into memory in advance. This is based on a predictive algorithm that uses information from the query execution plan to determine which pages are likely to be needed. Pre-Fetching : This mechanism anticipates the related data that will be needed for a query and reads it from related tables into memory in advance. This is based on the relationships defined in the query and can significantly reduce the number of I/O operations required during query execution. Parallelism : SQL Server can use multiple threads ...

Transport Layer Security (TLS) is a cryptographic protocol that provides secure communication over a network. TLS 1.3 is the latest version of the protocol, released in 2018, and it provides several improvements over the previous versions, including stronger encryption algorithms and a streamlined handshake process. In the context of SQL Server, TLS 1.3 can be used to secure the communication between the SQL Server instance and client applications, such as database management tools or web applications. When TLS 1.3 is enabled, all data exchanged between the client and server is encrypted and authenticated, protecting it from eavesdropping and tampering. To enable TLS 1.3 for SQL Server, you need to follow these steps : Install a certificate on the SQL Server instance: To use TLS 1.3, you need to have a certificate installed on the SQL Server instance. This certificate is used to authenticate the server to the client and to establish the encryption keys. Enable TLS 1.3 on the SQL Serv...

The Lock Manager in SQL Server is responsible for managing the locks that are acquired by transactions to ensure data consistency and integrity. When a transaction wants to access a data resource, it must first acquire a lock on that resource. The Lock Manager controls the acquisition and release of locks and ensures that concurrent transactions do not conflict with each other. The Lock Manager works by using different types of locks to manage the transactions. The two main types of locks used by the Lock Manager are Shared locks and Exclusive locks. Shared locks: A shared lock allows multiple transactions to read the same data resource simultaneously, but it prevents any transaction from modifying the data resource while the shared lock is held. Exclusive locks: An exclusive lock allows a single transaction to modify a data resource, preventing any other transactions from accessing or modifying the same resource until the exclusive lock is released. The Lock Manager uses a variety of...

The Log Manager in SQL Server is responsible for managing the transaction log, which is a critical component of the database. The transaction log records all the transactions that are performed on the database, including insertions, updates, and deletions, and it also records the time at which the change was made. In case of a system failure or error, the transaction log is used to recover the database to a consistent state. The Log Manager performs several tasks to ensure the integrity and consistency of the transaction log. These tasks include: Writing log records to the transaction log file: Whenever a transaction is executed, the Log Manager writes a log record to the transaction log file. The log record contains information about the transaction, including the type of transaction, the time at which it was executed, and the data that was changed. Flushing the log buffer: The Log Manager maintains a log buffer in memory, which stores the log records before they are written to the t...

In SQL Server, a " LOCK " is a mechanism used to ensure data consistency and prevent data corruption when multiple transactions access the same data concurrently. When a transaction needs to access a piece of data, it requests a lock on that data. If the data is already locked by another transaction, the requesting transaction may have to wait until the lock is released. There are several types of locks in SQL Server, including: Shared Lock : A shared lock allows multiple transactions to read the same data simultaneously, but it prevents any transaction from modifying the data until the lock is released. For example, when multiple transactions are reading from the same table, they acquire shared locks on the table to ensure that they don't interfere with each other. Exclusive Lock : An exclusive lock is acquired when a transaction needs to modify data, and it prevents any other transaction from reading or modifying the same data until the lock is released. For example, wh...

Rebuilding Index with Compression is a process in SQL Server that involves rebuilding an existing index on a table with the addition of data compression. This process can help reduce the size of the index, which in turn can help improve query performance and reduce storage costs. Here is an example of how to rebuild an index with compression in SQL Server: Assuming we have a table called "SalesData" with an index called "IX_SalesData_SalesDate", which we want to compress. 1) First, we need to identify the index we want to compress:     SELECT name, type_desc, is_disabled, compression_desc      FROM sys.indexes      WHERE object_id = OBJECT_ID('SalesData')      AND name = 'IX_SalesData_SalesDate'; This query retrieves information about the index, including its name, type, whether it is currently disabled, and its compression settings. 2) Next, we need to rebuild the index with compression:     ALTER INDEX IX_SalesData_Sa...