TempDB SQL Server Monitoring

TempDB is a database in SQL Server that stores temporary user objects, such as local or global temporary tables and stored procedures. It also holds the intermediate results of sorting operations, row versioning data for features like snapshot isolation level, and other transient data generated by users or the system. It gets recreated every time SQL Server restarts, so it does not maintain persistent state information between restarts. The system database "model" is used as a template when SQL Server creates databases.

TempDB data is organized into three categories:

• User data and objects: The activity of your devs, apps, and users
• Internal data and objects: The activity of the SQL Server
• Version store: A subset of internal data

There are also additional items can use TempDB that we may not be aware of, such as table variables and #temp tables which are both stored in TempDB within SQL Server.

Despite the potential for a SQL Server instance to have up to 32,767 distinct databases with thousands of processes running at any given time, field engineers frequently encounter instances of only 5,000 databases. This poses a performance risk, as SQL Server only has one TempDB acting as the "scratchpad" for every database and process on the instance. If not managed properly, this could result in TempDB becoming a single point of failure for the entire SQL Server instance.

The four common performance issues you may encounter in TempDB include:

Misconfiguration: The best practices for configuring TempDB can vary between major SQL Server versions. Many professionals will find multiple versions in their data centers or cloud providers, but proper configuration is key to TempDB performance regardless of version. Getting this right up front can dramatically reduce future run-ins with TempDB. Considerations such as size, number of data files, and storage performance are all important factors when avoiding common problems with TempDB.

Disk, Log, or Data Files Are Full (TempDB Full In SQL Server): TempDB is often overlooked or taken for granted because it usually functions as expected. However, DBAs are well aware of the potential issues that can arise when TempDB fails to operate properly. This is why we've brought attention to parasites because there is typically much more activity happening in TempDB than the workload your team has created and accounted for.

When a user database runs out of storage space, we tend to panic and hustle to fix one application—but what about TempDB? All too often, it's forgotten, which can lead to disastrous consequences when it runs out of space. TempDB can grow wildly due to a transaction that didn't roll back or from index maintenance. Therefore, proper capacity planning is essential for optimal TempDB performance.

PFS Page Contention: When discussing pages in SQL Server, we often immediately think of storage and IO. However, this scenario is more related to management objects. Data pages within the database track the allocation of storage and other objects. Since multiple threads can simultaneously compete for access to a single page, some operations may have to wait if there aren't enough data files providing sufficient throughput. This issue is exacerbated when TempDB allocates hundreds or thousands of tables frequently, resulting in users waiting longer in the application.

Availability Groups and Version Store Bloat: The version store is essential to understanding TempDB performance. This situation occurs when a transaction runs for too long or gets stuck, and the version store cleanup cannot be performed. As the name implies, the purpose of this cleanup is to remove old versions from the version store that are no longer necessary. Doing so frees up space in TempDB for new data and other objects. If this process does not occur, leftover versions will continue to accumulate until all available storage has been used up. For this reason, ongoing TempDB SQL Server monitoring is crucial for keeping a close eye on your TempDB performance.

Activity monitoring for TempDB includes many of the metrics that are important for SQL Server databases. Understanding the fundamentals of monitoring TempDB can help you know where to look for performance issues and how SQL Sentry Portal can help.

Configuration: Many of us still need to get our configuration and capacity planning right. Achieving peak performance in TempDB starts with ensuring it is optimally configured by following best practices.

Version Store: SQL Server system processes manage the version store and should be monitored separately from other internal and user data. Monitoring the size and change rate for the version store is crucial because it can quickly become large and volatile, causing significant performance issues.

Objects: Certain performance issues may arise when the version store is too large or too many tables are created over time. Monitoring version stores and tables separately from other objects in TempDB will help you identify these performance problems quickly.

Tables: When we first consider using TempDB, our thoughts often go to temporary tables. However, it also has system and internal work tables as well. The TempDB Objects chart in SentryOne Portal SQL Sentry Portal highlights storage consumed by the various tables and objects stored in TempDB to assist in TempDB SQL Server monitoring.

The same structures and data that make up other databases also make up TempDB.

Data in TempDB has a limited lifetime. User data can be scoped to a connection or globally. This affects who can access and manipulate the data and objects and how long they’re available. Temporary tables are scoped to the user who created it in the current session, whereas a global temp table is scoped to all users and all active sessions.