Queries have been running really slowly since upgrading the database to SQL Server 2025.

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Amin 10 Reputation points

After upgrading my SQL Server from versions 2014 and 2022 to 2025, the queries have become noticeably slower.

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Viorel 127K Reputation points

Is it a query that does not return many results?
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Erland Sommarskog 134.7K Reputation points • MVP • Volunteer Moderator
Did you also change the compatibility level from 120 to 170?

A good way to handle issues like this:

Keep compat level to 120.

Enable Query Store.

Run with compat level 120 a week or two.

Flip to 170.

You can now use Query Store to find regressed queries. and as a quick solution you can force the old plan.

You can also use the Tasks context menu for the database. At the bottom of the menu, you find Database Upgrade which helps you with the steps I outlined above.
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Amin 10 Reputation points

I noticed that when I use SQL Server Authentication, this problem occurs. When I add Trusted_Connection=True, the queries run normally; otherwise, they become really slow.
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Erland Sommarskog 134.7K Reputation points • MVP • Volunteer Moderator

While that is a hint, it is not sufficient to tell you what the issue is. It could be that there is an issue with SQL logins in SQL 2025, but I find it more likely that is a performance issue related to row-level security or similar.

You need to track down which queries that actually are slow.
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Amin 10 Reputation points

Everything was working fine with SQL Server 2022 (Windows or SQL Authentication mode), but this problem just happened in SQL Server 2025 using SQL Authentication mode!
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Erland Sommarskog 134.7K Reputation points • MVP • Volunteer Moderator

Do you want help with this, or do you only want to make a statement? If you only want to make a statement, we can stop here. If you want help, you need to help us to help you. Can you give an example of a query that is slow with SQL authentication, but runs quickly with Windows authentication?
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Akhil Gajavelly 1,830 Reputation points • Microsoft External Staff • Moderator
Hi @Amin ,

Thanks for the additional details. At this stage, @Erland Sommarskog have already covered the likely causes and the correct troubleshooting direction.

The difference between SQL Authentication and Windows Authentication by itself isn’t enough to diagnose the issue. To move this forward, we’ll need something concrete to compare specifically.

A sample query that is slow when executed using SQL Authentication

The same query running fast with Windows Authentication

Ideally, the execution plans (or Query Store plans) for both runs

Without a query and plan comparison, it’s not possible to determine whether this is related to SET options, security context (such as RLS or permissions), or plan caching behaviour in SQL Server 2025.

Once that information is available, the root cause should be straightforward to identify.

Thanks,
Akhil.
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Akhil Gajavelly 1,830 Reputation points • Microsoft External Staff • Moderator
Hi @Amin ,

Thanks for the additional details. At this stage, @Erland Sommarskog have already covered the likely causes and the correct troubleshooting direction.

The difference between SQL Authentication and Windows Authentication by itself isn’t enough to diagnose the issue. To move this forward, we’ll need something concrete to compare specifically.

A sample query that is slow when executed using SQL Authentication

The same query running fast with Windows Authentication

Ideally, the execution plans (or Query Store plans) for both runs

Without a query and plan comparison, it’s not possible to determine whether this is related to SET options, security context (such as RLS or permissions), or plan caching behavior in SQL Server 2025.

Once that information is available, the root cause should be straightforward to identify.

Thanks,
Akhil.
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Erland Sommarskog 134.7K Reputation points • MVP • Volunteer Moderator
Luca Domenichini, for more discussion on the effects of PBKDF2, see the thread https://learn.microsoft.com/en-us/answers/questions/5662030/sql-server-2025-executing-request-with-in-sql-conn.

Short story: It's a only a problem if:

You use SQL authentication.

You run many short requests.

You have turned off connection pooling.

All three are dubious practices, particularly the latter two.
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Akhil Gajavelly 1,830 Reputation points • Microsoft External Staff • Moderator

Hi @Amin,

Just checking in were you able to review the guidance regarding PBKDF2 impact and connection behavior?

As mentioned, the issue typically only surfaces when using SQL authentication with many short requests and connection pooling disabled. If you’re still experiencing the problem, please share your current setup and observations so we can help further.

Thanks,
Akhil.

Answer recommended by moderator

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Luca Domenichini 0 Reputation points

We are experiencing the same issue. Login latency is very noticeable.
Seen this on MS Learn:
https://learn.microsoft.com/en-us/sql/sql-server/sql-server-2025-known-issues?view=sql-server-ver17#pbkdf2-hashing-algorithm-can-affect-login-performance

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AI answer
After upgrading your SQL Server to version 2025, it's not uncommon to experience slower query performance. One potential cause could be related to changes in the Cardinality Estimation (CE) model that were introduced in SQL Server 2014 and continued in later versions. If your queries were optimized for an earlier version, they might not perform as well under the new CE model.

Here are some steps you can take to troubleshoot and potentially resolve the slow query performance:

Examine the query plan: Look at the execution plans for the slow-running queries to identify any inefficiencies.

Update Statistics: Ensure that the statistics for your tables are up to date, as outdated statistics can lead to poor query performance.

Identify Missing Indexes: Use the SQL Server Dynamic Management Views (DMVs) to find any missing indexes that could improve performance.

Rewrite Queries: Consider redesigning or rewriting the queries that are running slowly to optimize their performance.

Check Compatibility Level: Ensure that your database compatibility level is set appropriately for SQL Server 2025. Sometimes, reverting to a previous compatibility level can help improve performance until you can optimize the queries for the new version.

If all queries are running slower after the upgrade, the troubleshooting steps may differ, and you might need to investigate further into the specific causes of the performance degradation.

References:

Decreased query performance after upgrade from SQL Server 2012 or earlier to 2014 or later

Troubleshoot slow-running queries in SQL Server
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URL: https://learn.microsoft.com/en-us/answers/questions/5632977/queries-have-been-running-really-slowly-since-upgr?page=1

⇱ Queries have been running really slowly since upgrading the database to SQL Server 2025. - Microsoft Q&A

Queries have been running really slowly since upgrading the database to SQL Server 2025.

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