SQL Server Deadlock Monitoring Tool

Deadlocks in SQL Server occur when two or more transactions, or collections of SQL queries, block each other through a cyclical dependency. This happens when the transactions hold locks on resources the other transactions also need, resulting in a SQL Server lock on a table. A deadlocked SQL query cannot be completed until the lock is released, and neither can its fellow deadlocked SQL query.

When you get a SQL Server deadlock notification, you’ll find one transaction called the “victim” and one called the “survivor.” The victim is the session that gets rolled back, and it’s automatically selected by SQL Server based on deadlock priority and rollback cost.

Poor database design, a lack of indexing, inappropriate isolation levels, and poorly written queries are some common causes of deadlock. Whenever a SQL Server lock on a table occurs, operations are delayed or even stopped entirely. Eventually, deadlocks could result in a complete halt to processing inside your database engine.

Resolving SQL Server deadlocks can be a frustrating, time-consuming process, especially if you're dealing with multiple complex server deadlock scenarios. A typical deadlock situation unfolds in this way: one stored procedure has taken a lock on resource A (such as an object, page, or row) and is waiting on another procedure before it can access resource B. But the second procedure has a lock on B and is also waiting on the first procedure to release its lock on A.

To break this downward spiraling cycle, you need to quickly identify and address the source of the deadlock.

There are several ways to resolve SQL Server deadlocks depending on the situation. SQL Server is capable of automatic detection through a lock monitor. As noted above, as soon as a deadlock is detected, SQL Server automatically chooses the “victim” and rolls back that transaction—then it’s up to you and your IT administrative team to resolve deadlocks in SQL Server.

Here are some common ways to resolve SQL Server deadlocks:

• Covering indexes: By removing bookmark lookups entirely, a covering index can reduce your chances of deadlock caused by bookmark lookups.
• Foreign key indexes: Reduce SQL Server deadlock stemming from cascading referential integrity by creating indexes that match your foreign key columns. Without a foreign key index, cascading actions will take longer and increase the chances of a deadlock.
• Object order access: To create deadlocks for testing purposes, access database objects in a different order. To avoid these deadlocks otherwise, make transactions as short as possible and keep access objects in the same logical order.
• Transaction isolation levels: The default transaction isolation level on SQL Server, READ COMMITTED, can promote deadlocks between writers and readers of data. Avoid this by using COMMITTED SNAPSHOT or SNAPSHOT, in which a reader doesn’t take locks on objects and instead uses row versions for isolations.
• Deadlock priority: By specifying a transaction’s priority to High, Normal (Default), or Low, you can enable current sessions to continue processing if there’s SQL Server deadlock.
• Application error handling: Using TRY...CATCH logic, you could trap for the deadlock number. You could also set the number of retries allowed to a set number, reducing the chances of an infinite loop.

The best way to avoid deadlocks in SQL Server is to enlist the help of a SQL deadlocks monitoring tool. A SQL deadlock monitor can discover and resolve deadlocks in SQL Server by offering insights and capabilities that improve upon the deadlock monitoring.

There are some ways to find a lock in SQL Server without using a SQL deadlock monitor. These methods are performed through SQL Server itself:

• Trace flags: Through trace flags 1204 or 1222, SQL Server can perform deadlocks monitoring. Trace flags must be running at all times, making it hard to proactively detect deadlocks.
• Performance counter: This is designed to show the number of deadlocks present in SQL Server but doesn’t offer details regarding the session transactions involved.
• SQL Server profiler: Also known as a server-side trace, this can capture SQL Server deadlock details and display them in an XML graph. This method also has to run at all times, preventing you from proactively collecting metrics.
• Extended event session: SQL Server runs an extended event trace by default, but this method is time-consuming, prone to human error, and requires manual effort.

While these methods could offer some relief, they’re not as fast, easy, and efficient as using a deadlock monitoring tool to avoid deadlocks in SQL Server. A SQL deadlock detecting tool like SolarWinds SQL Sentry enables you to quickly recognize when a deadlock has occurred, understand its root causes, and see actions you can take to reduce the chances of a repeat deadlock.

Deadlock Analysis capabilities in SQL Sentry provide detailed metrics, so you can resolve server deadlocks and cut the time you spend restoring your database to peak performance. Metrics include:

• SQL Server where the deadlock took place
• Time the database deadlock occurred
• Victim SPID—the session process ID of the victim involved in the deadlock
• Victim host—workstation belonging to the victim thread
• Victim application—application name belonging to the victim thread
• Victim database
• Victim text data
• Deadlock XML—captured deadlock XML

The lock details area breaks down the database deadlock by specific lock types, including owners and waiters involved in each lock. Details include:

• SPID—session process ID of the associated owner/waiter
• Plan—opens a Plan Explorer session to view the associated query plan
• Host
• Application
• Database
• Log use—the amount of log space used by the process
• Deadlock priority—zero (0) or normal is the default priority
• Wait time—time in milliseconds spent waiting on the resource
• Transaction start time
• Last batch start time
• Last batch completion time
• Mode/type of resource lock
• Status of the task
• Current transaction isolation level
• Login name of the session

SolarWinds^® SQL Sentry is designed to capture and examine deadlocks quickly and thoroughly in SQL Server. Its SQL deadlock monitoring capabilities can help you detect and resolve deadlocks before they wreak havoc on your database operations and gain actionable insights into how to prevent similar deadlocks from occurring in the future.

SQL Sentry is built to use a modified Extended Event session to capture monitoring details. SQL Sentry is designed to display detected deadlocks at the bottom of the Trends tab, where you can find other critical SQL Server deadlock information such as:

• Time of deadlock occurrence
• Number of sessions involved in the deadlock
• Any objects involved
• Machine name and username

Another SQL Sentry metric is called Victim Impact, which is designed to show the measure of time a deadlocked transaction was running and consuming resources. Because transaction time means wasted resources, a SQL deadlock query victim’s transaction time is a good indicator of the impact the deadlock had on SQL Servers and any end users.

There are other pages alongside the Trends tab, where you can access more SQL Server deadlock actions and information. For instance, SQL Sentry enables you to configure non-default sessions using the Advanced Properties page. The SQL Sentry Deadlocks Details page is built to display the deadlock summary, which shows the victim and survivor’s time stamps, objects, programs, and number of sessions. Here you can also find data on the deadlocked resources including index name, database ID, lock ID.

SQL Sentry enables you to export key metrics and details which can be used in tandem with SQL Server Management Studio (SSMS). SSMS is software provided by Microsoft, which has the ability to migrate with SQL Sentry and other databases—through supporting SSMS integration, SQL Sentry can improve communication and optimize deadlock resolution. You could also send the deadlock details as an email through SQL Sentry and include the exported file as an email attachment.

Take full advantage of SQL Sentry to monitor various aspects of SQL Server operations to get a broad view of the elements affecting database performance.