Who should use this playbook
This guide is written for database administrators, data platform leads, and application owners who are responsible for production SQL Server instances and want to move to SQL Server 2025 without surprises. It assumes practical experience with backup and restore, basic performance metrics, and query tuning, but it explains each step in business friendly language so architects and managers can follow the decisions as well.
What is new in SQL Server 2025 that affects upgrades
SQL Server 2025 is version 17.0 of the database engine and introduces database compatibility level 170, which controls how the query optimiser behaves for each database. It is available on Windows, Linux, Docker, and Kubernetes, which allows more flexible deployment options than older versions.
Microsoft maintains support for compatibility certification using database compatibility levels, so you can move databases to SQL Server 2025 while still running them at an older compatibility level until you are ready to test the new optimiser behaviour.
Phase 1: Inventory and risk assessment
Start by creating an inventory of all instances and databases that you plan to move to SQL Server 2025, including version, edition, size, and criticality for each database. Note any use of special features such as full text search, columnstore indexes, replication, or external language integration, because some features may have edition specific limits or behaviour changes in SQL Server 2025.
Next, classify databases into tiers based on business impact, for example tier one for revenue or safety critical systems, tier two for important internal applications, and tier three for lower risk workloads and reporting environments. This classification will drive the order in which you upgrade and how cautious you need to be with compatibility changes and tuning steps.
Phase 2: Build and patch the SQL Server 2025 environment
Install SQL Server 2025 on new hardware or virtual machines that are sized appropriately for your workload and target edition. For many organisations, Standard Edition is attractive because in SQL Server 2025 it supports more memory and cores than previous versions, which reduces the need for Enterprise Edition in some scenarios.
After installation, apply the latest cumulative update so that you benefit from early fixes and engine improvements, not just the initial release version. Keep the operating system, storage drivers, and any associated tools such as SQL Server Management Studio (SSMS) at supported versions that understand SQL Server 2025 features.
Phase 3: Plan compatibility level strategy
Compatibility level is the main safety valve for query behaviour during an upgrade, because it allows the database engine version and the optimiser behaviour to be decoupled. The recommended pattern is to upgrade to SQL Server 2025 while leaving databases at their original compatibility level at first, then move databases to level 170 in controlled phases.
You can view and change the compatibility level with T-SQL similar to this example, replacing the database name and level with your values.
-- Check current compatibility level
SELECT name, compatibility_level
FROM sys.databases
WHERE name = N'YourDatabase';
-- Later, when ready, move to 170 for SQL Server 2025
ALTER DATABASE YourDatabase
SET COMPATIBILITY_LEVEL = 170;
GO
This approach gives you a clean line between pure engine changes and optimiser behaviour changes, which makes troubleshooting much easier if something slows down.
Phase 4: Enable Query Store before and after migration
Query Store is the central tool for detecting regressions when you change versions or compatibility levels, because it records query text, execution plans, and runtime statistics over time. If you are on a supported source version, turn on Query Store before the upgrade so that you capture a baseline of how queries behave today.
On SQL Server 2016 and later, you can enable Query Store like this.
ALTER DATABASE YourDatabase
SET QUERY_STORE = ON;
GO
ALTER DATABASE YourDatabase
SET QUERY_STORE (OPERATION_MODE = READ_WRITE);
GO
If Query Store is not available on the source system, you can restore a copy of the database to a test SQL Server 2025 instance with the old compatibility level and enable Query Store there to build a baseline under a representative workload.
Phase 5: Capture a performance baseline
Run your production workload for at least one to two weeks with Query Store enabled so that the system sees regular peaks, batch windows, and reporting periods. During this time, do not change the compatibility level, schema, or indexes; the goal is to capture how the workload behaves under stable conditions.
Use Query Store reports in SSMS, such as Top Resource Consuming Queries and Regressed Queries, to understand which procedures and statements are already expensive, even before the upgrade. Record key metrics such as average and ninety fifth percentile duration for critical queries, number of executions, and resource use so that you can compare them after you move to SQL Server 2025.
Phase 6: Move databases to SQL Server 2025 at old compatibility
When you are ready to move, migrate databases to SQL Server 2025 using backup and restore or database copy methods that preserve compatibility level and schema. After restoration, confirm that each database is still at the original compatibility level and that application connections succeed without code changes.
Turn on Query Store for any database that did not already have it, and let the workload run for several days while you monitor for errors, timeouts, and obvious slowdowns at the old compatibility level. This isolates engine level issues, such as changes in I O patterns or memory grants, from optimiser issues that will only appear after you raise compatibility.
Phase 7: Raise compatibility level in controlled batches
Once performance is stable at the old compatibility level on SQL Server 2025, select a small group of databases or a non critical environment and change the compatibility level to 170. Use maintenance windows and clear communication with application teams so that they know what to expect and can report issues quickly.
After the change, monitor Query Store for regressions using built in reports such as Regressed Queries, which highlight queries where runtime metrics such as duration or CPU increased significantly in the time window after the change compared to before. Consider a staged rollout where you first change compatibility for a pilot group, then expand to more databases once you have validated the process and resolved initial issues.
Phase 8: Detect regressions with Query Store
There are two complementary ways to use Query Store for regression detection. The first is graphical, using SSMS reports like Regressed Queries and Query Wait Statistics, which surface problematic queries visually and allow you to drill into execution plans. The second is query based, where you compare historical and recent runtime statistics for each query to flag regressions above a chosen threshold.
For example, you can write queries that compare average duration before and after the compatibility change and flag statements where recent average duration is more than fifty percent higher than historical duration. Focus your attention on queries that both regressed and have high resource use or business impact, since those are the ones that users will notice and that can destabilise the system.
Phase 9: Fix regressions with plan corrections and tuning
When Query Store shows a regressed query, compare the old and new execution plans side by side to see what changed, such as different join types, index use, or missing statistics. If the old plan is clearly better and still valid, you can use Query Store plan forcing so that SQL Server uses that plan for future executions while you investigate root causes.
On Enterprise Edition, you can also enable automatic tuning options such as FORCE_LAST_GOOD_PLAN, which let SQL Server automatically revert to a previous good plan when it detects regressions, but it is still important to monitor and understand what it changes. In parallel, apply classic tuning techniques such as updating statistics, adding or adjusting indexes, and reviewing parameter sniffing patterns to make sure that the new optimiser features in compatibility level 170 have the metadata they need to generate good plans.
Phase 10: SQL Server 2025 tuning checklist
After compatibility changes, run through a structured tuning checklist so that you are not only fixing regressions, but also taking advantage of SQL Server 2025 improvements. At a minimum, review these areas for each important database or instance.
- Instance configuration: validate max degree of parallelism, cost threshold for parallelism, memory limits, and tempdb configuration in the context of new engine behaviours and hardware capacity.
- Indexing: review missing index suggestions in execution plans, look for duplicated or unused indexes, and consider new indexing strategies that work well with recent engine improvements.
- Concurrency and locking: test workloads that suffered blocking on earlier versions, since SQL Server 2025 includes improvements in locking and tempdb resource governance that can reduce contention when configured correctly.
- Storage and I O: confirm that data files, log files, and tempdb are placed on appropriate storage tiers and that any new features that affect I O patterns in SQL Server 2025 are understood and tested in your environment.
For deeper query level tuning, refer readers to a dedicated SQL Server 2025 performance optimisation guide that covers index design patterns, memory grant analysis, tempdb tuning, and the use of new engine features in more detail, and link to that guide from this playbook.
Phase 11: Rollback and safety planning
Even with careful planning, you should prepare a clear rollback plan, especially for tier one systems. At the database level, you can temporarily revert the compatibility level to the previous value if regressions are severe and not quickly fixable, which often restores the old optimiser behaviour. At the instance or environment level, maintain recent full backups and, where possible, the ability to fall back to the previous version of SQL Server on separate hardware or virtual machines.
Document the conditions under which you will roll back, such as sustained performance below agreed thresholds or critical business operations being blocked, and agree on them with business stakeholders in advance so that there are no debates during an incident. This proactive planning makes the upgrade process more comfortable for non technical decision makers and reduces the pressure on the technical team during cutover windows.
How HariKrishna IT Solutions can help
HariKrishna IT Solutions focuses on SQL Server database design, optimisation, and version upgrades as core services, alongside full stack Microsoft development. The team is experienced in database migration and modernisation projects, including version upgrades and schema modernisation for enterprise workloads that cannot afford downtime or unpredictable performance.
For organisations planning a move to SQL Server 2025, HariKrishna IT Solutions can run structured assessments, design compatibility and Query Store strategies, execute the upgrade in phases, and then carry out detailed tuning based on the SQL Server 2025 performance optimisation guide so that the new platform not only matches but exceeds previous performance levels.
Suggested next steps
If you manage business critical SQL Server workloads and are considering SQL Server 2025, start by enabling Query Store and gathering a baseline on your current environment. Use the phases in this playbook to map out a realistic timeline and identify the right pilot systems for your first compatibility level changes.
When you are ready, engage a specialist team such as HariKrishna IT Solutions to review your plan, cross check it against the SQL Server 2025 optimisation guide, and co deliver the upgrade so that the combination of tool support and practical experience keeps regressions under control and leaves you with a faster, more stable data platform for the years ahead.