September 24, 2025 at 6:03 pm
We’re running SQL Server 2019 with database compatibility level 150, and after recent tuning (RAID-10 tempdb with even files and RCSI enabled) performance is stable; however our application vendor is asking us to drop the database’s compatibility level all the way down to 110 (SQL 2012). My concern is that this would disable many 2019 optimizer features and potentially cause new regressions. Is there any good reason to change the whole database to 110, or would it be better to keep 150 and handle any vendor-specific query with targeted options like QUERY_OPTIMIZER_COMPATIBILITY_LEVEL_110 or LEGACY_CARDINALITY_ESTIMATION (or plan forcing) instead? If you’ve been in this situation, what did you choose and what were the results—and would you recommend testing on a copy before making any change in production?
September 25, 2025 at 7:20 am
When the applications don't experience errors and end-user experience is satisfied about performance, I would leave it to the engine's db level ( 150 in your case ).
Before altering to a lower dblevel , I would ask for the vendors reasons and evidence to justify such action. ( and point to the fact that they are requesting for a database level that is aged )
Also involve the in-house software domain responsible that you got such a request. Chances are a software upgrade to a version that is "fully tested" to SQL2019 requires a budget they have not planned for.
Johan
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September 25, 2025 at 7:09 pm
Do they have a reason to change this? Perhaps they have code using keywords that changed?
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