SQL Server 2025 Added 10 Configuration Options, and One Appeared After RTM

· by · in

After an upgrade, a new sp_configure row can look more official than it really is. It has a name, a minimum, a maximum and a running value. It may even be dynamic. That still doesn’t tell me whether Microsoft expects me to change it, or whether the name is only enough for internal troubleshooting.

A woman DBA takes notes beside a mixing desk. Most sliders are labelled, and a group of new sliders at one end has blank labels, two of them glowing teal.

In the first post on SQL Server 2025, I compared the 2022 and 2025 system surface. This post continues the configuration-option check from the SQL Server 2022 version of this post. The whole series started with the first SQL Server 2022 inventory post.

sys.configurations is the system catalog view that returns one row for each server-wide configuration option. It includes the configured value, the running value, the minimum, the maximum, is_dynamic and is_advanced.[1]

My 2022 to 2025 diff found 10 configuration options that were present in SQL Server 2025 CU9 and absent from SQL Server 2022 CU25. It also found one changed option. Of the 11, four have their own option pages and two are listed in the server configuration table without a page of their own. One is used on a feature page but missing from the table, and I couldn’t find the exact names of the other four in the docs I checked.

How I checked

I used the same inventory files from the series opener. The 2022 instance is SQL Server 2022 CU25 Enterprise. The 2025 instance is SQL Server 2025 CU9 Enterprise Developer. CU means cumulative update. I also checked the SQL Server 2025 RTM inventory, where RTM means the initial release with no cumulative update.

For the count, I filtered pairwise.csv to Series = 2022-2025, Kind = new, and Cat = configuration. For the range and advanced-option flag, I read the matching rows from the tab-separated inventory files. Then I ran this read-only query against the 2025 instance. It returned the current running value and the is_dynamic flag:

For documentation, I checked the live Microsoft Learn server configuration options page, the sp_configure page and each option page or feature page I could find. I also searched the SQL Server, Azure and Fabric documentation source repositories with whole-word fixed-string git grep searches for each option name, plus a case-insensitive search where Learn used different capitalization.[2][3]

The 2025 rows

This table combines four sources: the 2022 to 2025 diff, the 2025 CU9 inventory range, the live sys.configurations query, and the documentation check I ran on September 26, 2026.

Option 2025 CU9 range Advanced Dynamic value_in_use Documentation class
ADR cleaner lock timeout (s) 1 to 32767 Yes Yes 5 Not found
SLOG memory quota (%) 1 to 100 Yes Yes 75 Not found
allow server scoped db credentials 0 to 1 No Yes 0 Row in table only
availability group commit time (ms) 0 to 10 Yes Yes 0 Own page
external AI runtimes enabled 0 to 1 No Yes 0 Feature page only, not in the table
external rest endpoint enabled 0 to 1 No Yes 0 Row in table only
max UCS send boxcars 256 to 2048 Yes No 256 Own page
max lock manager cache memory (%) 20 to 60 Yes No 20 Own page
max server tiered memory (MB) 0 to 2147483647 Yes No 2147483647 Not found
tiered memory enabled 0 to 1 Yes No 0 Not found

The changed row is backup compression algorithm. SQL Server 2022 had a maximum value of 2. SQL Server 2025 has a maximum value of 3. The Learn page says value 3 selects the Zstandard (ZSTD) compression algorithm in SQL Server 2025.[4]

max lock manager cache memory (%) is the only configuration option in this list that appeared between 2025 RTM and CU9. It is absent from the RTM inventory and present in the CU9 inventory. Microsoft documents it as available in SQL Server 2025 CU5 and later.[5]

The documented ones are mostly availability group and memory controls

availability group commit time (ms) has its own page. Microsoft says SQL Server 2025 adds this option to set the group commit time, in milliseconds, for an Always On availability group replica. The page says the default value of 0 means SQL Server uses 10 ms.[6]

max UCS send boxcars also has its own page. UCS is Universal Communication Service. The page says SQL Server uses it for Always On availability groups to send log blocks between primary and secondary replicas. The page also says the sp_configure option starts in SQL Server 2025. A registry override existed in SQL Server 2022.[7]

The max lock manager cache memory (%) page gives the clearest version boundary in this group. The page says SQL Server 2025 CU5 and later limit the lock manager cache to 20 percent by default. It also says previous versions and pre-CU5 SQL Server 2025 can let the lock manager cache grow to 60 percent of total SQLOS committed memory.[8]

I still test before changing any of these three, but I can at least read the intended scope, the default behaviour and the version boundary.

The AI and REST rows are uneven

external rest endpoint enabled is linked from the server configuration options table to the sys.sp_invoke_external_rest_endpoint page. That page says the stored procedure is available in SQL Server 2025 and Azure SQL Managed Instance. It is disabled by default, and enabled with sp_configure 'external rest endpoint enabled', 1.[9]

allow server scoped db credentials has no option page, but it appears in the server configuration options table. Feature pages use it, including the PolyBase managed identity page. That page says SQL Server 2025 can use managed identity to access Azure Blob Storage and Azure Data Lake. It lists this option as a prerequisite.[10]

external AI runtimes enabled is the odd row. The CREATE EXTERNAL MODEL page contains an example that runs sp_configure 'external AI runtimes enabled', 1, but the option was not on the live server configuration options page when I checked. I also couldn’t find an option page for it. Microsoft documents related SQL Server 2025 AI features, including CREATE EXTERNAL MODEL and AI_GENERATE_EMBEDDINGS. I found only one exact hit for the option name in the SQL Server docs source.[11]

The rows I still can’t explain

I couldn’t find documentation for four exact option names: ADR cleaner lock timeout (s), SLOG memory quota (%), max server tiered memory (MB) and tiered memory enabled. I searched the live server configuration page, likely option-page names, and the SQL Server, Azure and Fabric docs source repositories. The only tiered-memory matches I found were SQL Server 2025 error-message rows. They were not documentation for the two configuration options.[12]

ADR cleaner lock timeout (s) is separate from the documented ADR cleaner options I found. Microsoft documents ADR cleaner retry timeout (min) and ADR Preallocation Factor. I couldn’t find a page or table row for ADR cleaner lock timeout (s).[13]

The tiered-memory pair looks like it belongs together because one option enables the feature and the other caps server tiered memory. That is a name-based observation only. I didn’t find a public source that explains the feature, supported editions, platforms or operational guidance. I wouldn’t change either option from the name alone.

SLOG is another name I won’t expand without a source. The option is present in SQL Server 2025 RTM and CU9, with a running value of 75 on my 2025 instance. I couldn’t find the exact option name, or enough public context around it, in the checked sources.

How I treat these

A row in sys.configurations tells me what the instance accepts. It doesn’t tell me whether to use it. For the rows with option pages, I can evaluate the documented behaviour and decide whether the setting belongs in an upgrade review. For rows that only appear on feature pages, I start with that feature page. I don’t treat it as full guidance for changing the option.

For the rows I couldn’t find, I leave them alone unless Microsoft Support tells me otherwise. A name can help me decide what to research next, but I don’t change a server option from the name alone.

Next, I’m checking LCK_M_SCH_A and LCK_M_SCH_C in SQL Server 2025.

Have you found a public page for one of the rows I missed, or did one of these appear in your upgrade review? Tell me on Bluesky or LinkedIn, and I’ll update the notes.

References

  1. sys.configurations (Transact-SQL) - Microsoft Learn. Defines the configuration catalog view and the value, value_in_use, minimum, maximum, is_dynamic and is_advanced columns used in the query. ↩
  2. Server Configuration Options - SQL Server, Azure SQL Managed Instance and sys.sp_configure (Transact-SQL) - Microsoft Learn. The live pages checked before the documentation-source search. ↩
  3. MicrosoftDocs/sql-docs, MicrosoftDocs/azure-docs and MicrosoftDocs/fabric-docs - GitHub. The Markdown source of Microsoft Learn for SQL Server, Azure and Fabric, searched with whole-word, fixed-string git grep on 2026-09-26. The search results are my own. ↩
  4. Server Configuration: Backup Compression Algorithm - Microsoft Learn. Documents backup compression algorithm, including value 3 for ZSTD in SQL Server 2025. ↩
  5. Server Configuration: max lock manager cache memory (%) - Microsoft Learn. Documents that the option is available in SQL Server 2025 CU5 and later. ↩
  6. Server Configuration: availability group commit time (ms) - Microsoft Learn. Documents the SQL Server 2025 option and says value 0 uses the default 10 ms group commit time. ↩
  7. Server Configuration: max ucs send boxcars - Microsoft Learn. Documents the SQL Server 2025 option, explains UCS flow control and describes the earlier SQL Server 2022 registry override. ↩
  8. Server Configuration: max lock manager cache memory (%) - Microsoft Learn. Explains the lock manager cache limit and previous behaviour. ↩
  9. sys.sp_invoke_external_rest_endpoint (Transact-SQL) - Microsoft Learn. Documents the procedure and says SQL Server 2025 enables it with external rest endpoint enabled. ↩
  10. Configure PolyBase Support for Managed Identity - Microsoft Learn. Lists allow server scoped db credentials as a prerequisite for managed identity access to Azure Blob Storage and Azure Data Lake in SQL Server 2025. ↩
  11. CREATE EXTERNAL MODEL (Transact-SQL) and AI_GENERATE_EMBEDDINGS (Transact-SQL) - Microsoft Learn. The CREATE EXTERNAL MODEL page includes an sp_configure example for external AI runtimes enabled. The AI_GENERATE_EMBEDDINGS page documents the related AI feature. ↩
  12. MicrosoftDocs/sql-docs, MicrosoftDocs/azure-docs and MicrosoftDocs/fabric-docs - GitHub. The Markdown source of Microsoft Learn for SQL Server, Azure and Fabric, searched with whole-word, fixed-string git grep on 2026-09-26. The search results are my own. ↩
  13. Server Configuration: ADR cleaner retry timeout (min) and Server Configuration: ADR Preallocation Factor - Microsoft Learn. The documented ADR configuration pages checked while looking for ADR cleaner lock timeout (s). ↩
Tags: , , ,