Overview of the Azure SQL Architecture:

Azure SQL Database is a fully managed relational database service provided by Microsoft Azure. Its architecture is designed to provide scalability, high availability, and security for hosting relational databases in the cloud.

Azure Data Centers: Azure SQL Database runs on Microsoft's global network of data centers, which are distributed across multiple regions worldwide. These data centers provide the physical infrastructure for hosting Azure SQL Database instances and ensure high availability and fault tolerance.

SQL Database Engine: At the core of Azure SQL Database is the SQL Database Engine, which is based on the same SQL Server database engine used in on-premises deployments. The engine manages database operations, query processing, data storage, and security functions.

Managed Service Layer: Azure SQL Database is a fully managed service, which means that Microsoft handles infrastructure management, maintenance, and monitoring tasks. The managed service layer includes features such as automated backups, patching, high availability, and disaster recovery to ensure optimal performance and reliability.

Elastic Scaling: Azure SQL Database offers elastic scaling capabilities, allowing databases to scale compute and storage resources dynamically based on workload demand. Users can adjust the performance tier (e.g., Basic, Standard, Premium, Serverless) and storage size of their databases without downtime to accommodate changing requirements.

Security Features: Azure SQL Database includes built-in security features to protect data from unauthorized access, such as Transparent Data Encryption (TDE), Always Encrypted, Dynamic Data Masking (DDM), Row-Level Security (RLS), and Azure Active Directory (Azure AD) authentication. These features help organizations enforce data privacy and compliance with regulatory requirements.

High Availability and Disaster Recovery: Azure SQL Database ensures high availability and disaster recovery through features such as automatic backups, geo-replication, and automatic failover. Automated backups allow users to restore databases to any point in time within the retention period, while geo-replication replicates databases asynchronously to secondary regions for disaster recovery purposes.

Integration with Azure Services: Azure SQL Database integrates with other Azure services such as Azure Key Vault, Azure Monitor, Azure Resource Manager, and Azure Active Directory for enhanced security, monitoring, management, and automation capabilities.

Compatibility with SQL Server: Azure SQL Database offers near-complete compatibility with SQL Server, including support for T-SQL, stored procedures, triggers, views, and data types. This enables seamless migration of existing SQL Server workloads to Azure SQL Database with minimal changes.

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 

                                                                                                            Download

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.