Common SQL Server wait types

In SQL Server, wait types are events or conditions that cause a task (such as a query or a process) to wait for a specific resource or event to be available before it can continue processing. Monitoring and analyzing wait types can help identify performance bottlenecks and optimize the database system.

Here are some common SQL Server wait types:

  1. PAGEIOLATCH_XX:
    • Description: Indicates that a process is waiting for a data page to be read from disk into memory.
    • Possible Causes: Slow I/O subsystem, high disk latency.
  1. CXPACKET:
    • Description: Related to parallel query execution. Indicates that a parallel query is waiting for another thread to complete its work.
    • Possible Causes: Overloaded parallelism, uneven workload distribution.
  1. LCK_XX:
    • Description: Indicates a process is waiting to acquire a lock on a resource.
    • Possible Causes: Contentious locks due to high concurrency.
  1. ASYNC_NETWORK_IO:
    • Description: Indicates a task is waiting for network packets to be sent or received.
    • Possible Causes: Slow or congested network.
  1. WRITELOG:
    • Description: Indicates a process is waiting for a log flush to complete.
    • Possible Causes: High transaction log activity, slow disk write performance.
  1. SOS_SCHEDULER_YIELD:
    • Description: Indicates that a task voluntarily yielded the scheduler to let other tasks run.
    • Possible Causes: High CPU usage, resource contention.
  1. PAGE_VERIFY:
    • Description: Indicates a task is waiting for a page verification operation to complete.
    • Possible Causes: Configuring database option CHECKSUM and experiencing high I/O.
  1. OLEDB:
    • Description: Indicates a task is waiting for an OLE DB operation to complete.
    • Possible Causes: Issues with external data source or linked server.
  1. WAITFOR:
    • Description: Indicates a task is waiting for a specified amount of time to elapse.
    • Possible Causes: Delays introduced in queries using the WAITFOR statement.

Monitoring and analyzing wait types can be done using dynamic management views (DMVs) such as sys.dm_os_wait_stats. By querying these views, you can identify which wait types are causing the most contention and focus on optimizing those areas for better performance. Additionally, tools like SQL Server Profiler and Extended Events can be used for more in-depth analysis of wait statistics.

What is the Lazy Writer in SQL Server?

The Lazy Writer is a vital background process in SQL Server, designed to optimize the efficiency of the buffer pool. The buffer pool is a crucial memory area where SQL Server caches data pages, reducing the need to repeatedly read data from disk.

Here’s how the Lazy Writer operates:

  • Purpose: Its primary role is to manage the buffer pool by handling clean pages (data pages that have been modified but not yet written to disk).

  • Function: The Lazy Writer periodically moves aged and less frequently accessed data pages from the buffer pool to disk. This helps free up space in the buffer pool for new, more actively used data pages.

  • Benefits: By performing this cleanup, the Lazy Writer helps maintain the performance and efficiency of SQL Server, ensuring that the buffer pool is optimized for handling incoming data requests.

In essence, the Lazy Writer keeps your SQL Server running smoothly by ensuring that memory resources are used effectively and that new data can be cached efficiently.

The Role of a SQL Server Database Administrator (DBA)

A SQL Server Database Administrator (DBA) is essential for managing and maintaining SQL Server databases within an organization. The specific responsibilities can vary based on the organization's size and structure, but generally, a SQL Server DBA handles the following tasks:-

Database Installation and Configuration

  • Install and Configure SQL Server: Set up SQL Server instances following best practices.
  • Optimize Settings: Configure server and database settings to enhance performance and security.

Database Design

  • Collaborate with Developers: Work with developers and system architects to design efficient, normalized database structures.
  • Manage Database Objects: Create and modify tables, views, indexes, and stored procedures.

Security Management

  • Implement Security Policies: Manage roles, permissions, and security policies at both server and database levels.
  • Review Access: Regularly audit and review database access to ensure compliance and security.

Backup and Recovery

  • Develop Strategies: Create and execute backup and recovery plans to ensure data integrity and availability.
  • Test Disaster Recovery: Document and test procedures to handle potential disasters.

Performance Monitoring and Optimization

  • Monitor Performance: Use tools and logs to monitor server and database performance.
  • Resolve Bottlenecks: Identify and address performance issues through indexing, query optimization, and tuning.

High Availability and Disaster Recovery

  • Implement Solutions: Set up high availability solutions like clustering, mirroring, or AlwaysOn Availability Groups.
  • Plan for Recovery: Develop and test disaster recovery plans to minimize data loss and downtime.

Patch Management and Upgrades

  • Apply Updates: Install patches and updates to maintain SQL Server security and stability.
  • Execute Upgrades: Plan and manage version upgrades as needed.

Automation and Scripting

  • Develop Scripts: Create and maintain scripts for routine tasks, monitoring, and automation.
  • Streamline Tasks: Use PowerShell or other scripting languages to automate administrative functions.

Documentation

  • Maintain Records: Keep comprehensive documentation of databases, configurations, and procedures.
  • Ensure Accessibility: Ensure documentation is current and accessible to relevant stakeholders.

Capacity Planning

  • Monitor Growth: Track database growth and plan for necessary capacity upgrades.
  • Forecast Needs: Predict future capacity requirements based on usage trends.

Troubleshooting and Incident Response

  • Resolve Issues: Investigate and resolve database-related problems and incidents.
  • Respond to Outages: Provide timely responses to system outages or performance issues.

Training and Knowledge Sharing

  • Stay Informed: Keep up with new features and best practices in SQL Server.
  • Train Others: Conduct training sessions and share knowledge with team members and developers.

Navigating the Linux File System Hierarchy: A Beginner's Guide 🌐

 For IT professionals and Linux enthusiasts, mastering the Linux file system hierarchy is key to efficient system management. Unlike the physical layout on disk, the Linux file system is organized logically, starting from the root directory /.

Here’s a snapshot of the core directories and their functions:

  1. /bin 🛠️: Contains essential system binaries like bash, ls, and grep.
  2. /boot 🚀: Houses boot essentials such as the kernel image and bootloader.
  3. /dev 🔌: A hub for device files representing connected hardware.
  4. /etc 📜: The directory for system configuration files.
  5. /home 🏠: Stores user home directories.
  6. /lib 📚: Contains shared libraries used by various programs.
  7. /media 💿: Mount points for removable media like CDs and USB drives.
  8. /mnt 🧲: Used for temporary filesystem mounts.
  9. /opt 📦: Houses optional software packages.
  10. /proc 📊: Information central for system processes and memory usage.
  11. /root 👑: The home directory for the root user.
  12. /sbin 🔧: Contains system administration binaries like init and fdisk.
  13. /srv 🌐: Data storage for services like web servers.
  14. /tmp 🌡️: A space for temporary files.
  15. /usr 🖥️: Most user-installed software is found here.
  16. /var 🔄: Holds variable data such as logs and temporary files.

Useful Commands

  • ls — List directory contents.
  • cd — Change directory.
  • pwd — Print working directory.
  • mkdir — Make a new directory.
  • rm — Remove files or directories.
  • cp — Copy files or directories.
  • mv — Move or rename files or directories.
  • cat — Concatenate and display files.
  • chmod — Change file or directory permissions.
  • chown — Change file or directory ownership.
  • grep — Search for patterns in files.
  • top — Display system processes.
  • ps — Display running processes.
  • kill — Terminate processes.
  • sudo — Execute a command as a superuser.
  • du — Estimate file space usage.
  • tar — Create or extract archive files.
  • ping — Test network connectivity.
  • vi — Edit files using a text editor.
  • ssh — Connect to remote servers securely.

Tips for Navigating the Linux File System

  • cd 🚶: Navigate directories.
  • ls 📋: List directory contents.
  • mkdir 📁: Create a directory.
  • rmdir 🗑️: Remove a directory.
  • cp 📤: Copy files/directories.
  • mv 🚚: Move files/directories.
  • rm: Delete files/directories.

⚠️ Caution: Some directories, like /bin, are read-only. Avoid altering their contents to prevent system issues!

Understanding this hierarchy is crucial for efficient Linux system management. Dive into the Linux file system to enhance your skills and streamline your workflows! 🌟




How To Send SQL Server CPU Utilization Alerts Using SQL Server Agent

 This article explains how to send an email alert using SQL Server alerts when the SQL Server CPU utilization reaches a specific threshold.

In Microsoft SQL Server, you can use T-SQL and SQL Server Agent to generate an alert when CPU usage exceeds a threshold, such as 80%. Here's an example of how you can achieve this:

Create a SQL Server Agent alert: Open SQL Server Management Studio (SSMS) and connect to your SQL Server instance. Navigate to the SQL Server Agent node in the Object Explorer, right-click on the "Alerts" folder, and select "New Alert."

Configure the alert properties: In the "New Alert" dialog, configure the following properties:

Name: Provide a name for the alert.

Type: Select the type of alert as "SQL Server performance condition alert."

Object: Choose the "Resource Pool Stats."

Counter: Choose the "CPU Usage target %" counter.

 Instance: Select "default" to monitor the overall CPU usage of the entire system.

Alert if counter: Choose "Rises above" to trigger the alert when CPU usage exceeds the threshold.

Value: Enter "0.8" to set the threshold for CPU usage to 80%.

 Enable this alert: Check this option to enable the alert.

Response: Choose the appropriate response action, such as "Notify operators" or "Execute job" to determine what action should be taken when the alert is triggered.

Additional actions: As needed, you can configure additional actions, such as sending an email or running a script.

Click on "OK" to create the alert.

Once the alert is created, SQL Server Agent will automatically monitor the CPU usage based on the specified threshold. When the CPU usage exceeds 80%, the alert will be triggered, and the configured response action will be executed, such as sending notifications or running a script.

T-SQL Stored Procedure To Send CPU-Intensive Queries

Let us understand this with a simple demonstration. Suppose I want to create an alert when the CPU utilization reaches 80%; the SQL Server automatically sends the alert along with the list of the top 10 CPU-intensive queries. We will email the queries in an HTML table.

We can use the following query to populate the top 10 CPU-intensive queries list.


SELECT TOP 10 session.session_id, 

           req.cpu_time, 

           req.logical_reads, 

           req.reads, 

           req.writes, 

           SUBSTRING(sqltext.TEXT, (req.statement_start_offset / 2) + 1, 

           ((CASE req.statement_end_offset 

                WHEN -1 THEN DATALENGTH(sqltext.TEXT) 

                ELSE req.statement_end_offset 

            END - req.statement_start_offset) / 2) + 1) AS statement_text, 

           COALESCE(QUOTENAME(DB_NAME(sqltext.dbid)) + N'.' + QUOTENAME(OBJECT_SCHEMA_NAME(sqltext.objectid, sqltext.dbid))  

           + N'.' + QUOTENAME(OBJECT_NAME(sqltext.objectid, sqltext.dbid)), '') AS command_text, 

       req.command, 

           session.login_name, 

           session.host_name, 

           session.program_name, 

           session.last_request_end_time,

           session.login_time   

FROM sys.dm_exec_sessions AS session 

JOIN sys.dm_exec_requests AS req ON req.session_id = session.session_id CROSS APPLY sys.Dm_exec_sql_text(req.sql_handle) AS sqltext 

WHERE req.session_id != @@SPID 

ORDER BY req.cpu_time DESC 

Query Output:



The entire stored procedure is following:

USE ajay --- change Database

 go

 Create PROCEDURE Sp_send_highcpu_alert

 AS

   BEGIN

       CREATE TABLE #tbl_highcpu_query_output

         (

            sessionid             INT,

            cpu_time              BIGINT,

            logicalreads          BIGINT,

            reads                 BIGINT,

            writes                BIGINT,

            querystatement        VARCHAR(max),

            command_text          VARCHAR(max),

            command               VARCHAR(1500),

            login_name            VARCHAR(1000),

            hostname              VARCHAR(50),

            program_name          VARCHAR(500),

            last_request_end_time DATETIME,

            login_time            DATETIME

         )

       INSERT INTO #tbl_highcpu_query_output

       SELECT TOP 10 session.session_id,

                     req.cpu_time,

                     req.logical_reads,

                     req.reads,

                     req.writes,

                     Substring(sqltext.text, ( req.statement_start_offset / 2 ) +

                                             1

                     , (

                     (

                     CASE req.statement_end_offset

                       WHEN -1 THEN Datalength(sqltext.text)

                       ELSE req.statement_end_offset

                     END - req.statement_start_offset ) / 2 ) + 1)

                     AS statement_text,

                     COALESCE(Quotename(Db_name(sqltext.dbid)) + N'.'

                              + Quotename(Object_schema_name(sqltext.objectid,

                              sqltext.dbid))

                              + N'.'

                              + Quotename(Object_name(sqltext.objectid,

                              sqltext.dbid)),

                     '') AS

                     command_text,

                     req.command,

                     session.login_name,

                     session.host_name,

                     session.program_name,

                     session.last_request_end_time,

                     session.login_time

       FROM   sys.dm_exec_sessions AS session

              JOIN sys.dm_exec_requests AS req

                ON req.session_id = session.session_id

              CROSS apply sys.Dm_exec_sql_text(req.sql_handle) AS sqltext

       WHERE  req.session_id != @@SPID

       ORDER  BY req.cpu_time DESC


       DECLARE @HTMLString NVARCHAR(max)

       DECLARE @SUBJECT VARCHAR(max) = 'High CPU Alert on: ' + @@servername + '.'


       SET @HTMLString= '   <H2>Top 10 CPU Intesnive Queries</H2>   <table id="AutoNumber1" borderColor="#111111" border="1">      <tr>     <td bgcolor="#99CC33">session ID</td>     <td bgColor="#99CC33">CPU Time</td>     <td bgcolor="#99CC33">Logical Reads<</b></td>     <td bgcolor="#99CC33">Reads</td>     <td bgcolor="#99CC33">Writes</td>     <td bgcolor="#99CC33">Query Statement</td>     <td bgcolor="#99CC33">Stored Procedure</td>     <td bgcolor="#99CC33">Command</td>     <td bgcolor="#99CC33">Login name</td>     <td bgcolor="#99CC33">hostname</td>     <td bgColor="#99CC33">program_name</td>     <td bgcolor="#99CC33">last_request_end_time</b></td>     <td bgcolor="#99CC33">login_time</td>      </tr>'

                        + Cast((SELECT DISTINCT td = sessionid, ' ', td= cpu_time

                        ,

                        ' ',

                        td = logicalreads, ' ', td = reads, ' ', td = writes, ' '

                        ,

                        td =

                        querystatement, ' ', td = command_text, ' ', td = command

                        ,

                        ' ',

                        td = login_name, ' ', td = hostname, ' ', td=

                        program_name,

                        ' '

                        , td = last_request_end_time, ' ', td = login_time, ' '

                        FROM

                        #tbl_highcpu_query_output WHERE program_name NOT LIKE

                        '%Mail%'

                        FOR xml path('tr'), type) AS NVARCHAR(max))

                        + '</table>'


       SELECT @HTMLString


       -- Send email using sp_send_dbmail  

       EXEC msdb.dbo.Sp_send_dbmail

         @profile_name = 'SQLmail',

         -- Replace with the name of your DbMail profile  

         @recipients = 'sqldbanow@gmail.com',

         @subject = @subject,

         @body = @HTMLString,

         @body_format = 'HTML';

   END 


Configure Alert

Create a database alert, as I explained at the article's beginning. The alert parameters should be as shown in the screenshot below.



When the alert is raised, we want to send the list of CPU-intensive queries. To do that, we must create an SQL Job. I have created a SQL Server Agent job named Populate_High_CPU_Queries. The SQL Job executes the sp_send_HIGHCPU_Alert stored procedure.

In our case, the job step should look like the following image:



Once the SQL job named Populate_High_CPU_Queries is created, you can specify the job name in the response option of the alert. Below is the image of the Response tab for reference.


Sample Email report