Side-by-side migration in the context of SQL Server using Backup and restore

 Side-by-side migration in the context of SQL Server using Backup and restore 

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Capture all SQL and Stored Proc calls using Extended Events in SQL Server

-- Capture all SQL and Stored Proc calls

-- Part of the SQL Server DBA Toolbox at https://github.com/DavidSchanzer/Sql-Server-DBA-Toolbox

-- This script creates an Extended Events session called "CaptureAllSQLAndStoredProcCalls" that includes the following events:

-- error_reported (for severity 20 and above, as well as certain error numbers)

-- existing_connection

-- login

-- logout

-- rpc_completed

-- sql_batch_completed

CREATE EVENT SESSION [CaptureAllSQLAndStoredProcCalls]

ON SERVER

    ADD EVENT sqlserver.error_reported

    (ACTION

     (

         package0.callstack,

         sqlserver.client_app_name,

         sqlserver.client_hostname,

         sqlserver.database_name,

         sqlserver.nt_username,

         sqlserver.session_id,

         sqlserver.session_nt_username,

         sqlserver.sql_text,

         sqlserver.tsql_stack,

         sqlserver.username

     )

     WHERE (

               [severity] >= (20)

               OR

               (

                   [error_number] = (17803)

                   OR [error_number] = (701)

                   OR [error_number] = (802)

                   OR [error_number] = (8645)

                   OR [error_number] = (8651)

                   OR [error_number] = (8657)

                   OR [error_number] = (8902)

                   OR [error_number] = (41354)

                   OR [error_number] = (41355)

                   OR [error_number] = (41367)

                   OR [error_number] = (41384)

                   OR [error_number] = (41336)

                   OR [error_number] = (41309)

                   OR [error_number] = (41312)

                   OR [error_number] = (41313)

               )

           )

    ),

    ADD EVENT sqlserver.existing_connection

    (ACTION

     (

         package0.event_sequence,

         sqlserver.client_hostname,

         sqlserver.session_id

     )

    ),

    ADD EVENT sqlserver.login

    (SET collect_options_text = (1)

     ACTION

     (

         package0.event_sequence,

         sqlserver.client_hostname,

         sqlserver.session_id

     )

    ),

    ADD EVENT sqlserver.logout

    (ACTION

     (

         package0.event_sequence,

         sqlserver.session_id

     )

    ),

    ADD EVENT sqlserver.rpc_completed

    (SET collect_statement = (1)

     ACTION

     (

         package0.event_sequence,

         sqlserver.client_app_name,

         sqlserver.client_hostname,

         sqlserver.database_name,

         sqlserver.nt_username,

         sqlserver.session_id,

         sqlserver.session_nt_username,

         sqlserver.sql_text,

         sqlserver.tsql_stack,

         sqlserver.username

     )

     WHERE ([package0].[equal_boolean]([sqlserver].[is_system], (0)))

    ),

    ADD EVENT sqlserver.sql_batch_completed

    (ACTION

     (

         package0.event_sequence,

         sqlserver.client_app_name,

         sqlserver.client_hostname,

         sqlserver.database_name,

         sqlserver.nt_username,

         sqlserver.session_id,

         sqlserver.session_nt_username,

         sqlserver.sql_text,

         sqlserver.tsql_stack,

         sqlserver.username

     )

     WHERE ([package0].[equal_boolean]([sqlserver].[is_system], (0)))

    )

    ADD TARGET package0.event_file

    (SET filename = N'c:\temp\CaptureAllSQLAndStoredProcCalls.xel')

WITH

(

    MAX_MEMORY = 16384KB,

    EVENT_RETENTION_MODE = ALLOW_SINGLE_EVENT_LOSS,

    MAX_DISPATCH_LATENCY = 5 SECONDS,

    MAX_EVENT_SIZE = 0KB,

    MEMORY_PARTITION_MODE = PER_CPU,

    TRACK_CAUSALITY = ON,

    STARTUP_STATE = OFF

);

GO 

Here are key points about the buffer cache in SQL Server:

    The buffer cache in SQL Server is a part of the SQL Server memory architecture that is responsible for caching database pages in memory. When SQL Server reads data from a disk, it stores a copy of that data in the buffer cache. Subsequent queries that need the same data can then be served from the in-memory buffer rather than reading from disk, which is significantly faster.

Here are key points about the buffer cache in SQL Server:

Buffer Pool:

The buffer cache is often referred to as the "buffer pool" or "data cache." It is a region in the SQL Server memory space dedicated to storing data pages.

Pages and Extents:

SQL Server divides its storage into fixed-size pages (usually 8 KB). These pages are grouped into larger structures called extents. The buffer cache holds these pages in memory.

Data Access:

When a query needs data, SQL Server first checks if the required pages are already in the buffer cache. If the data is present, it's called a "cache hit," and the data can be retrieved quickly from memory. If not, it's a "cache miss," and the data must be read from disk.

Read-Ahead Mechanism:

SQL Server uses a read-ahead mechanism to anticipate and pre-fetch pages into the buffer cache before they are needed. This helps to minimize the impact of physical I/O on query performance.

LRU (Least Recently Used) Algorithm:

The buffer cache uses an LRU algorithm to manage the contents of the cache. When the cache becomes full, pages that haven't been used recently are candidates for removal to make room for new pages.

Dirty Pages and Checkpoints:

When modifications are made to data in the buffer cache, the modified pages become "dirty." SQL Server periodically writes these dirty pages back to the data files during a process called a checkpoint. This ensures that changes are persisted to disk.

Monitoring Buffer Cache:

Performance monitoring tools and DMVs (Dynamic Management Views) can be used to monitor the state of the buffer cache. For example, the sys.dm_os_buffer_descriptors view provides information about the pages currently in the buffer cache.

SELECT * FROM sys.dm_os_buffer_descriptors;

Configuring Buffer Cache:

SQL Server provides configuration options for the size and behavior of the buffer cache. The "max server memory" configuration option limits the amount of memory that SQL Server can use for the buffer cache.

sp_configure 'max server memory', <value>;

The buffer cache plays a crucial role in optimizing SQL Server performance by reducing the need to perform expensive disk I/O operations. Properly configuring and monitoring the buffer cache is important for maintaining optimal database performance.

Here are common SQL Server performance issues and potential solutions:

 SQL Server performance issues can arise for various reasons, and resolving them often involves identifying bottlenecks, optimizing queries, and configuring the server appropriately. Here are common SQL Server performance issues and potential solutions:

High CPU Usage:

Issue: Excessive CPU utilization.

Solutions:

Identify and optimize poorly performing queries.

Consider adding indexes to improve query performance.

Scale up resources (CPU, memory).

Review and adjust the SQL Server configuration for parallelism.

Memory Pressure:

Issue: Insufficient available memory for SQL Server.

Solutions:

Configure SQL Server memory settings appropriately.

Identify and optimize memory-consuming queries.

Monitor and adjust memory-related configuration settings.

I/O Bottlenecks:

Issue: Slow disk I/O affecting query performance.

Solutions:

Optimize queries to reduce I/O load.

Consider adding more/faster disks.

Use storage with higher IOPS capabilities.

Review and optimize file placement, such as database and log files.

Blocking and Deadlocks:

Issue: Transactions waiting on locks, leading to performance degradation.

Solutions:

Optimize queries and transactions.

Use appropriate isolation levels.

Monitor and identify blocking using tools like SQL Server Profiler.

Implement proper indexing.

Inefficient Query Plans:

Issue: SQL Server generates suboptimal query execution plans.

Solutions:

Update statistics to ensure accurate query plans.

Use index hints to force specific indexes.

Rewrite queries to improve performance.

Indexing Issues:

Issue: Missing or poorly designed indexes.

Solutions:

Regularly analyze and create missing indexes.

Remove unnecessary indexes to improve write performance.

Use the Database Engine Tuning Advisor (DTA) to recommend index changes.

TempDB Contention:

Issue: High contention in the TempDB database.

Solutions:

Split TempDB data files equally across multiple disks.

Adjust the number of TempDB files based on CPU cores.

Monitor and optimize queries that heavily use TempDB.

Out-of-date Statistics:

Issue: Query optimizer relies on outdated statistics.

Solutions:

Regularly update statistics on tables and indexes.

Consider enabling the AUTO_UPDATE_STATISTICS database option.

Network Latency:

Issue: Slow communication between the application and the database.

Solutions:

Optimize network infrastructure.

Use the appropriate network protocols.

Consider deploying closer Azure regions for Azure SQL Database.

Fragmented Indexes:

Issue: Fragmentation affecting index scan/seek performance.

Solutions:

Regularly rebuild or reorganize fragmented indexes.

Monitor index fragmentation using DMVs.

Long-running Queries:

Issue: Queries taking too long to execute.

Solutions:

Optimize queries using proper indexing.

Use execution plans to identify and address performance bottlenecks.

Insufficient Server Resources:

Issue: Not enough CPU, memory, or disk resources.

Solutions:

Consider upgrading hardware or moving to a larger VM size.

Optimize queries to use resources more efficiently.

Regular monitoring, proper configuration, and ongoing performance tuning are essential for maintaining optimal SQL Server performance. It's often helpful to use tools like SQL Server Profiler, SQL Server Management Studio (SSMS), and dynamic management views (DMVs) to diagnose and address performance issues. Additionally, regularly reviewing and implementing best practices for SQL Server performance can help prevent and mitigate potential problems.

Version control in SQL Server

 Version control in SQL Server refers to the practice of managing and tracking changes to database objects, such as tables, views, stored procedures, and functions, over time. Using version control helps in maintaining a history of changes, collaborating with multiple developers, and rolling back to previous states if needed. Here are common approaches and tools for version control in SQL Server:

1. Scripting and Source Control Systems:

• Manual Scripting: Developers manually create and maintain SQL scripts for database objects. These scripts are then stored in a version control system such as Git.
• Source Control Integration: Many version control systems offer integrations with SQL Server Management Studio (SSMS) or other database development tools. Developers can directly commit changes to version control from within the tool.

2. Database Projects in Visual Studio:

• SQL Server Data Tools (SSDT): Visual Studio includes a project type known as SQL Server Data Tools, which allows developers to create and manage database projects. These projects can be version-controlled using Git, TFS (Team Foundation Server), or other source control systems.

3. Migrations and Change Tracking:

• Database Migrations: Tools like FluentMigrator, DbUp, or Entity Framework Migrations can be used to create scripts that represent changes to the database schema. These scripts can be version-controlled and applied in a structured manner.
• Change Tracking: SQL Server has built-in features like Change Data Capture (CDC) and Change Tracking that can help track changes to data. While not a complete version control solution, these features complement version control practices.

4. Third-Party Tools:

• Redgate SQL Source Control: This tool integrates with SSMS and supports popular version control systems. It allows developers to link databases to version control repositories and track changes.
• Liquibase and Flyway: These are database migration tools that support version control for databases. They use scripts or configurations to manage changes and can be integrated with source control systems.

5. Git Hooks and Database CI/CD:

• Git Hooks: Pre-commit and post-commit hooks in Git can be used to automate checks and tasks related to version control, such as running tests, enforcing coding standards, or triggering continuous integration (CI) builds.
• Database CI/CD: Implementing a continuous integration and continuous delivery (CI/CD) pipeline for databases helps automate the process of deploying database changes from version control to different environments.

When implementing version control for SQL Server, it's essential to establish best practices, including documentation, naming conventions, and a clear process for branching and merging. Regularly syncing the database schema with version control and ensuring that changes are traceable are critical aspects of effective version control practices.