Nullable columns in a database cost you ISNULL calls and OR IS NULL conditions in every query. This post lists them with a catalog query, compares the INFORMATION_SCHEMA version, and counts the real NULLs in each column. The count tells you which columns can become NOT NULL and which can go.
APPROX_COUNT_DISTINCT With GROUP BY: When Exact Wins
APPROX_COUNT_DISTINCT with GROUP BY returns an estimate for every group. A tested demo on 2,000,000 rows shows a memory grant of 207,616 KB for the exact count against 3,112 KB for the estimate, and a memory grant of 0 for the exact count once an index exists. It also shows the error on small groups, where 4,648 of 100,000 groups were off.
Queries Waiting for Memory: Read the Grant Counters
Queries waiting for memory are counted by the Memory Grants Pending counter and listed by sys.dm_exec_query_memory_grants. A tested demo holds a sort grant of 41,848 KB with a blocked query and reads it from the view. The post explains how to spot a waiting request and what causes the wait.
Row Mode Memory Grant Feedback: It Needs Level 150
Row mode memory grant feedback needs compatibility level 150 or higher, while batch mode needs only 140. A tested demo runs a row mode sort and a batch mode sort at levels 140, 150 and 170. The row sort keeps its grant of 11,888 KB at level 140 and drops to 1,536 KB at 150.
What is the Priority of Database Scoped Configurations? – Interview Question of the Week #254
Question: What is the Priority of Database Scoped Configurations over Global Configuration at Server Level?
Answer: This is a follow-up question.
Database Scoped Configuration Options in SQL Server
Database scoped configuration options change how one database behaves, without touching the server. This post lists all 41 options on SQL Server 2025, finds the 7 ids that are missing, and changes and restores two settings in a demo database. It also answers the old question about configuration id 5.
Missing tempdb Files: master_files vs database_files
Missing tempdb files show up as a mismatch between sys.master_files and tempdb.sys.database_files. This post compares the two with a query, simulates the missing files on a copy of the catalog, and shows the error log message that gives the cause. The fix is to correct the path and restart.