In this blog post, we will discuss an issue encountered with an Always On Availability Group where a database remained stuck in the Initializing / In Recovery state on the secondary replica after a failover. We will explore the steps taken to resolve the problem and provide insights into the underlying causes.
Issue
During a failover from the primary to the secondary replica in an Always On Availability Group, one particular database entered the Initializing / In Recovery state on the secondary replica. Despite restarting SQL services and attempting to suspend data movement, the database remained stuck in this state.
Resolution
Logging off users and restarting SQL services: Initially, all users were logged off from the secondary replica, and the SQL services on the replica were restarted. However, these steps did not resolve the issue.
Suspending data movement: The next approach involved suspending the data movement of the problematic database from the SQL Server Management Studio on the secondary replica. However, this operation resulted in a “lock request time out period exceeded” error.
Identifying the blocking process: To investigate further, a query was executed to identify any blocking processes using the following query: SELECT * FROM sysprocesses WHERE blocked > 0 It was discovered that the DB Startup thread for the specific database was blocking the SPID attempting to suspend data movement.
Checking recovery status: The SQL Server error log was examined to determine if the database’s recovery had completed. The log indicated that recovery for the database had finished in 43 seconds, with no user action required. Recovery completed for database JB_DB (database ID 7) in 43 second(s) (analysis 64 ms, redo 324 ms, undo 0 ms.) This is an informational message only. No user action is required.
Analyzing DB Startup thread wait type: Monitoring the DB Startup thread revealed that it was in a wait state with the HADR_RECOVERY_WAIT_FOR_UNDO type. This wait type occurs when the secondary database is waiting for the reverting and initializing phases to synchronize with the primary database after failover.
Monitoring undo progress: The “Log remaining for undo” performance monitor counter was used to track the amount of log in kilobytes remaining for the undo phase. Surprisingly, the counter showed 0, indicating that there was nothing to undo, and the recovery completed message in the SQL Server error log confirmed that the undo took 0 milliseconds.
Failing over to another synchronous secondary replica: To further troubleshoot the issue, a failover was performed from the primary replica to another synchronous secondary replica. This time, all databases returned to a synchronized state without any issues.
Summary
The issue of a database stuck in the Initializing / In Recovery state after an Always On Availability Group failover was resolved by failing over to another synchronous secondary replica. Although the root cause and exact timing of the issue remain unknown, this blog post aims to provide guidance and assistance to others who may encounter similar challenges within the community.
Thank You, Vivek Janakiraman
Disclaimer: The views expressed on this blog are mine alone and do not reflect the views of my company or anyone else. All postings on this blog are provided “AS IS” with no warranties, and confers no rights.
SQL Server 2022 has arrived with a myriad of exciting performance enhancements that are set to revolutionize database management. In this article, we will explore the various aspects of these enhancements, their significance in the realm of database management, and the benefits they offer to businesses and organizations. From query optimizer improvements to in-memory enhancements, storage enhancements, security upgrades, scalability improvements, and integration with cloud technologies, we will dive into the details of each feature and understand how they contribute to elevating the performance of SQL Server.
Overview of SQL Server 2022
To begin our journey, let’s take a moment to understand SQL Server 2022. It is the latest iteration of Microsoft’s flagship relational database management system, known for its robustness, reliability, and scalability. SQL Server 2022 builds upon the strengths of its predecessors and introduces an array of performance-enhancing features that address common challenges faced in database management.
Importance of Performance Enhancements in Database Management
Performance is a crucial aspect of any database management system. Slow queries, inefficient data retrieval, and inadequate scalability can hinder the overall productivity and efficiency of an organization. Recognizing this, SQL Server 2022 has placed a strong emphasis on performance enhancements, aiming to deliver lightning-fast query execution, improved optimization, and enhanced data processing capabilities. These enhancements enable businesses to extract insights from their data more efficiently, leading to better decision-making and ultimately, a competitive edge.
Understanding SQL Server Performance
Before delving into the specifics of SQL Server 2022’s performance enhancements, it is important to familiarize ourselves with the key metrics used to evaluate database performance. Metrics such as response time, throughput, and resource utilization provide valuable insights into the efficiency and effectiveness of the database system. Additionally, we will explore common performance challenges encountered in SQL Server, including suboptimal query plans, index fragmentation, and contention issues, which the enhancements in SQL Server 2022 aim to address.
Introducing SQL Server 2022 Performance Enhancements
Now let’s take a closer look at the performance enhancements introduced in SQL Server 2022.
Overview of New Features and Enhancements
SQL Server 2022 introduces an impressive array of new features and enhancements that have been designed to tackle the performance challenges faced by organizations. These advancements span various aspects of the database engine, including the query optimizer, in-memory processing, storage operations, security, scalability, and integration with cloud technologies. By comprehensively addressing these areas, SQL Server 2022 aims to optimize performance and provide a seamless and efficient user experience.
Benefits of Upgrading to SQL Server 2022
Upgrading to SQL Server 2022 brings numerous benefits for businesses. Enhanced query optimization ensures improved query plans and faster execution, resulting in reduced response times and increased overall database performance. In-memory enhancements provide accelerated data access and manipulation, allowing for real-time analytics and quicker decision-making. Storage enhancements, such as resumable index operations and intelligent indexing, minimize downtime and optimize space utilization. Furthermore, the security enhancements bolster data protection and compliance, safeguarding sensitive information from unauthorized access.
Query Optimizer Enhancements
The query optimizer is at the heart of SQL Server’s performance. In SQL Server 2022, the query optimizer has received significant enhancements to improve cardinality estimation, adapt to changing workload patterns through adaptive query processing, and employ intelligent query processing techniques. These advancements result in more accurate query plans, optimal resource allocation, and overall improved query performance.
Improved Cardinality Estimation
Cardinality estimation plays a critical role in determining the optimal query plan. SQL Server 2022 introduces improvements in cardinality estimation algorithms, enabling the query optimizer to make better-informed decisions about data distribution and selectivity. This results in more accurate cardinality estimates, which ultimately lead to improved query plans and better query performance.
Adaptive Query Processing
Workload patterns can vary significantly over time, making it challenging to create a single static query plan that remains optimal under all circumstances. Adaptive query processing, a new feature in SQL Server 2022, allows the database engine to adapt dynamically to changing conditions. It enables the optimizer to adjust query plans based on actual runtime statistics, ensuring optimal performance even in the face of varying data and query patterns.
Intelligent Query Processing
Intelligent query processing takes performance optimization to the next level by employing intelligent algorithms and techniques. Features like batch mode on rowstore, table variable deferred compilation, and memory grant feedback leverage machine learning and intelligent algorithms to optimize query execution and resource allocation. These advancements result in faster query processing, reduced CPU and memory usage, and overall improved performance.
In-Memory Enhancements
In-memory processing has gained significant popularity in recent years due to its ability to deliver lightning-fast data access. SQL Server 2022 further enhances in-memory capabilities with features like accelerated database recovery and memory-optimized Tempdb metadata.
Accelerated Database Recovery
Database recovery after a failure or crash can be a time-consuming process. SQL Server 2022 introduces accelerated database recovery, which drastically reduces the time required for recovery by utilizing a novel log-based recovery mechanism. This enhancement ensures minimal downtime and faster database availability, leading to improved overall system performance and resilience.
Memory-Optimized Tempdb Metadata
Tempdb is a crucial component of SQL Server, used for temporary storage and sorting operations. In SQL Server 2022, memory-optimized Tempdb metadata enables faster metadata operations by leveraging memory-optimized technology. This enhancement improves concurrency, reduces contention, and speeds up Tempdb-related operations, leading to enhanced performance and scalability.
Storage Enhancements
Efficient storage operations are vital for optimal database performance. SQL Server 2022 introduces several storage enhancements that address common challenges, such as resumable index operations, intelligent indexing, and accelerated database recovery for big data clusters.
Resumable Index Operations
Creating or rebuilding indexes on large tables can be a time-consuming process, often leading to significant downtime. With resumable index operations in SQL Server 2022, administrators can pause and resume index operations, allowing for greater flexibility and minimizing the impact on database availability. This enhancement enables organizations to perform index maintenance tasks efficiently without disrupting ongoing operations.
Intelligent Indexing
Creating and maintaining indexes is a critical aspect of database optimization. SQL Server 2022 introduces intelligent indexing, which automates the index management process by analyzing query patterns and recommending optimal indexes. This feature simplifies index management, improves query performance, and reduces manual effort required for index maintenance.
Accelerated Database Recovery for Big Data Clusters
Big data clusters require robust storage and recovery mechanisms to handle large volumes of data. SQL Server 2022 provides accelerated database recovery specifically tailored for big data clusters, significantly reducing the time required for database recovery operations. This enhancement ensures faster data availability and improves the performance of big data workloads.
Security Enhancements
Data security is of paramount importance in today’s digital landscape. SQL Server 2022 introduces security enhancements that further fortify the protection of sensitive data, including features like Always Encrypted with Secure Enclaves and dynamic data masking improvements.
Always Encrypted with Secure Enclaves
Always Encrypted is a feature introduced in previous versions of SQL Server that allows sensitive data to be encrypted at rest and in transit. In SQL Server 2022, Always Encrypted with Secure Enclaves takes data security to a whole new level. By leveraging secure enclaves, SQL Server can perform computations on encrypted data without exposing the plaintext to the outside world. This feature provides an additional layer of security and ensures that sensitive data remains protected throughout its lifecycle.
Dynamic Data Masking Improvements
Dynamic data masking is a feature that allows organizations to mask sensitive data in real-time, ensuring that only authorized individuals can view the actual values. SQL Server 2022 introduces improvements to dynamic data masking, providing more granular control over data masking rules and enhancing the flexibility and effectiveness of data protection mechanisms.
Enhanced Availability and Scalability
High availability and scalability are crucial for mission-critical applications that demand continuous uptime and the ability to handle growing workloads. SQL Server 2022 introduces enhancements in these areas to meet the evolving needs of modern businesses.
High Availability Enhancements
SQL Server 2022 introduces several high availability enhancements, including improved failover capabilities, enhanced resiliency, and simplified management. Features like accelerated database recovery, always-on availability groups, and enhanced automatic failover mechanisms ensure continuous availability of critical databases, minimizing downtime and improving overall system reliability.
Scalability Improvements
As data volumes and user concurrency increase, scalability becomes a key consideration for any database system. SQL Server 2022 incorporates scalability improvements that enable organizations to scale their databases vertically and horizontally. These enhancements, such as improved parallelism, increased resource utilization, and optimized query processing, ensure that SQL Server can handle growing workloads efficiently and deliver consistent performance.
Sharding Improvements
Sharding is a technique used to horizontally partition large databases across multiple servers, enabling distributed data storage and parallel processing. SQL Server 2022 introduces improvements in sharding capabilities, providing enhanced support for sharded databases, simplified management, and improved query performance. These enhancements enable organizations to leverage the power of distributed computing and achieve seamless scalability for their applications.
Integration with Cloud Technologies
With the increasing adoption of cloud computing, SQL Server 2022 offers enhanced integration with cloud technologies to provide organizations with the flexibility and scalability required for modern data platforms.
Hybrid Cloud Capabilities
SQL Server 2022 enables seamless integration between on-premises and cloud environments through its hybrid cloud capabilities. Organizations can leverage features like Azure Arc-enabled data services to manage and operate their SQL Server instances from a centralized location. This integration allows for a unified management experience and the ability to extend on-premises SQL Server deployments to the cloud, providing greater agility and scalability.
SQL Server 2022 and Azure Integration
SQL Server 2022 integrates tightly with Microsoft Azure, unlocking a wide range of cloud-based services and capabilities. Organizations can leverage Azure SQL Database and Azure Synapse Analytics to offload certain workloads, take advantage of cloud-based analytics and machine learning, and benefit from built-in automation and scalability features. This integration empowers organizations to leverage the power of the cloud while maintaining the familiarity and capabilities of SQL Server.
Performance Tuning Best Practices
Optimizing the performance of a SQL Server database requires a combination of best practices, tools, and techniques. SQL Server 2022 introduces various performance tuning features and improvements, which, when combined with established best practices, can deliver outstanding performance.
Analyzing and Optimizing Query Performance
Analyzing and optimizing query performance is a critical task for database administrators. SQL Server 2022 provides advanced tools and techniques for query tuning, including query plan analysis, index optimization, and statistics management. By understanding the query execution plans, identifying bottlenecks, and applying appropriate optimizations, administrators can significantly enhance query performance and overall system efficiency.
Monitoring and Tuning Indexes
Indexes play a vital role in query performance. SQL Server 2022 offers comprehensive indexing capabilities, including tools for index monitoring, analysis, and optimization. By monitoring index usage, identifying fragmented or redundant indexes, and optimizing index design, administrators can improve data retrieval speed, reduce disk I/O, and boost overall database performance.
Utilizing Query Store for Performance Insights
Query Store, introduced in previous versions of SQL Server, is a powerful tool for query performance monitoring and troubleshooting. SQL Server 2022 enhances the capabilities of Query Store, providing administrators with valuable insights into query performance, plan regressions, and historical trends. By utilizing Query Store, administrators can identify and rectify performance issues, track query behavior over time, and ensure optimal performance for their databases.
Conclusion
In conclusion, SQL Server 2022 introduces a wide range of performance enhancements that address common challenges in database management. From query optimizer improvements to in-memory enhancements, storage enhancements, security upgrades, scalability improvements, and integration with cloud technologies, these enhancements pave the way for faster query execution, improved resource utilization, enhanced data access, and superior overall performance.
By upgrading to SQL Server 2022 and leveraging its performance-enhancing features, organizations can unlock new possibilities, optimize their databases, and stay ahead in today’s data-driven landscape. It is crucial for businesses to explore and leverage these benefits to maximize their productivity, gain valuable insights, and maintain a competitive edge in their respective industries.
Thank You, Vivek Janakiraman
Disclaimer: The views expressed on this blog are mine alone and do not reflect the views of my company or anyone else. All postings on this blog are provided “AS IS” with no warranties, and confers no rights.
SQL Server Accelerated Database Recovery (ADR) is a feature introduced in SQL Server 2019 that enhances the database recovery process. ADR addresses the long-standing challenge in SQL Server of database recovery time increasing with the number of transactions and active connections to the database. ADR helps minimize downtime during database recovery and reduces the risk of data loss.
This article will provide an in-depth look at SQL Server Accelerated Database Recovery, including its background, challenges and opportunities, best practices, future outlook, and conclusion.
Traditionally, when SQL Server experiences a crash or an unexpected shutdown, the database goes through a recovery process that can take a long time to complete. The recovery process involves three phases: analysis, redo, and undo. During the analysis phase, SQL Server scans the transaction log to determine the point at which the database was last consistent. In the redo phase, SQL Server applies all the transactions that were committed after that point. Finally, in the undo phase, SQL Server rolls back any transactions that were not committed.
The time it takes to complete the recovery process depends on the size of the transaction log, the number of transactions, and the number of connections to the database. In some cases, the recovery process can take hours or even days to complete, causing significant downtime for the application and potentially resulting in data loss.
Explanation of database recovery Whenever a SQL Server instance restarts, the databases that were online before the restart must undergo a recovery process. During the recovery process, SQL Server ensures that all committed transactions are written to disk and any uncommitted transactions are rolled back. This ensures that the database is brought back to a consistent state.
Overview of SQL Server Accelerated Database Recovery SQL Server Accelerated Database Recovery is a feature introduced in SQL Server 2019 that improves database recovery times and availability. It accomplishes this by reducing the amount of log data that needs to be replayed during recovery and by allowing recovery from a checkpoint.
Benefits of SQL Server Accelerated Database Recovery The primary benefits of SQL Server Accelerated Database Recovery are faster recovery times and improved availability. This feature significantly reduces the downtime associated with database recovery and allows organizations to restore their systems more quickly in the event of a failure.
Understanding Traditional Database Recovery
Traditional database recovery involves restoring the database from a backup and replaying all the transactions in the log since the last backup.
How traditional database recovery works In traditional database recovery, SQL Server reads the transaction log to identify all transactions that were not committed at the time of the restart. SQL Server then rolls back all uncommitted transactions and applies all committed transactions to the database. This process can take a significant amount of time, depending on the size of the database and the number of transactions that were in progress at the time of the restart.
Limitations of traditional database recovery Traditional database recovery has several limitations. It can take a long time to complete, especially for large databases. In addition, the recovery process can cause a significant amount of I/O activity, which can impact the performance of the server. Finally, if a failure occurs during the recovery process, the entire recovery process must be restarted.
How SQL Server Accelerated Database Recovery Works
Log Sequence Number (LSN) filtering SQL Server Accelerated Database Recovery works by filtering out redundant transaction log records during the recovery process. This is accomplished through the use of Log Sequence Number (LSN) filtering, which is a feature that was introduced in SQL Server 2019.
When a database is in Accelerated Database Recovery mode, SQL Server maintains a version store, which is a collection of active and previous versions of data pages. Each version of a data page is identified by its LSN, which is a unique identifier assigned to each transaction log record.
During the recovery process, SQL Server filters out transaction log records that are already reflected in the version store. This means that only changes that occurred after the most recent checkpoint are replayed during recovery, which can significantly reduce the amount of time required for recovery.
Checkpoint process Another key aspect of SQL Server Accelerated Database Recovery is the checkpoint process. Checkpoints are a mechanism used by SQL Server to write dirty data pages (i.e., data pages that have been modified but not yet written to disk) to disk. This helps to reduce the amount of work required during recovery, as it ensures that there is less dirty data to be written to disk when the recovery process begins.
With Accelerated Database Recovery, the checkpoint process is enhanced to include a special type of checkpoint called a Accelerated Database Recovery checkpoint. These checkpoints are optimized for use with Accelerated Database Recovery, and they help to ensure that the version store is properly maintained and that redundant transaction log records are filtered out during recovery.
Recovery with Accelerated Database Recovery enabled When a database is in Accelerated Database Recovery mode, recovery is performed in a slightly different way than it is with traditional database recovery. Instead of replaying all transaction log records from the beginning of the log, SQL Server uses the version store to filter out redundant records and only replays the necessary changes.
This can result in significantly faster recovery times, particularly for large databases or databases with high transaction rates. In addition, because only necessary changes are replayed, there is minimal impact on workload during the recovery process.
Benefits of SQL Server Accelerated Database Recovery
Faster recovery times One of the primary benefits of SQL Server Accelerated Database Recovery is faster recovery times. By filtering out redundant transaction log records and replaying only necessary changes, SQL Server can significantly reduce the amount of time required to recover a database.
This is particularly beneficial for large databases or databases with high transaction rates, as traditional database recovery can take a significant amount of time in these scenarios. With Accelerated Database Recovery, recovery times can be reduced from hours or even days to minutes.
Improved availability Another benefit of SQL Server Accelerated Database Recovery is improved availability. Because recovery times are significantly reduced, databases can be back up and running more quickly after a failure.
This can help to minimize downtime and ensure that critical business processes are not impacted by database failures. In addition, because only necessary changes are replayed during recovery, there is minimal impact on workload during the recovery process, which further improves availability.
Minimal impact on workload With traditional database recovery, there is a significant impact on workload during the recovery process. This is because all transaction log records must be replayed from the beginning of the log, which can result in significant resource usage.
With SQL Server Accelerated Database Recovery, only necessary changes are replayed during recovery, which significantly reduces the impact on workload. This means that business processes can continue to operate normally during the recovery process, which is particularly important for mission-critical applications.
Implementation of SQL Server Accelerated Database Recovery
Implementing SQL Server Accelerated Database Recovery is a straightforward process, but there are a few requirements to keep in mind.
Compatibility requirements First, your SQL Server instance must be running on at least SQL Server 2019 Enterprise Edition or Azure SQL Database. Additionally, your database must be running in the compatibility level 150 or higher.
Enabling Accelerated Database Recovery To enable Accelerated Database Recovery for a specific database, use the following T-SQL command:
ALTER DATABASE [DatabaseName] SET ACCELERATED_DATABASE_RECOVERY = ON;
Once enabled, Accelerated Database Recovery is applied to all operations performed against the database. This includes all transactional operations, such as inserts, updates, and deletes, as well as DDL operations, such as table creation or index rebuilding.
Monitoring Accelerated Database Recovery SQL Server provides several mechanisms for monitoring the performance of Accelerated Database Recovery.
One useful tool is the sys.dm_tran_persistent_version_store_stats dynamic management view. This view provides detailed statistics on the size and utilization of the version store for a specific database, as well as information about any background cleanup processes that may be running.
Additionally, SQL Server Management Studio provides a graphical view of the version store in the form of a new tab in the database properties window. This tab shows real-time statistics on the version store size and utilization, as well as the total number of versions and the oldest active transaction.
Limitations of SQL Server Accelerated Database Recovery
While Accelerated Database Recovery provides many benefits, there are also a few limitations to keep in mind.
Unsupported database features Not all database features are supported with Accelerated Database Recovery. For example, databases that use memory-optimized tables, table partitioning, or stretch database are not currently supported.
Increased disk space usage Accelerated Database Recovery can result in increased disk space usage due to the version store, which stores multiple versions of each modified page. This increased disk space usage may require additional planning and monitoring for large databases with high transactional volumes.
Potential performance impact In rare cases, Accelerated Database Recovery may cause a performance impact due to increased I/O operations required for log processing. However, this impact is typically minimal and is outweighed by the benefits of faster recovery times and improved availability.
Conclusion
SQL Server Accelerated Database Recovery provides a powerful new feature for improving database recovery times and reducing downtime. By leveraging innovative technology such as Log Sequence Number (LSN) filtering and persistent versioning, Accelerated Database Recovery enables faster and more reliable database recovery with minimal impact on workload.
While there are a few limitations to keep in mind, such as unsupported database features and increased disk space usage, the benefits of Accelerated Database Recovery far outweigh the potential drawbacks. If you’re running SQL Server 2019 Enterprise Edition or Azure SQL Database, consider enabling Accelerated Database Recovery to take advantage of its powerful benefits and improve your database’s availability and performance.
Disclaimer: The views expressed on this blog are mine alone and do not reflect the views of my company or anyone else. All postings on this blog are provided “AS IS” with no warranties, and confers no rights.
