Short explanations of SQL Server problems you’ll meet in production. Each page says what the problem looks like, why it happens, what fixes it and what doesn’t, and gives a query to check your own server.
Every page is backed by a runnable demo in sqlserver-demos on GitHub. The demo reproduces the problem on purpose, measures each fix, and checks its own predictions, and CI reruns the demos on SQL Server 2019, 2022 and 2025. The numbers on these pages were measured, not assumed.
These pages and the demos were written with the help of AI. Every number on them comes from running the demos on SQL Server, not from the AI. See how this was made.
The library
- Accelerated Database Recovery
- Backup and restore
- Blocking a query with ABORT_QUERY_EXECUTION (SQL Server 2025)
- Blocking chains
- Capping tempdb with Resource Governor (SQL Server 2025)
- Catch-all queries
- Columnstore and the delta store
- Correlated predicates
- Data compression
- Data type traps
- Deadlock patterns
- Fuzzy string matching (SQL Server 2025)
- Heaps and forwarded records
- Implicit conversions
- Index fragmentation
- Key lookups and the tipping point
- Lock escalation
- Memory grants sized by declared width
- Minimal logging
- Missing-index suggestions
- MSTVFs and table variables
- New T-SQL syntax traps (SQL Server 2025)
- Non-SARGable predicates
- Optimized locking (SQL Server 2025)
- Optional parameter plans (SQL Server 2025)
- Ordered columnstore indexes (SQL Server 2022 and 2025)
- Pagination: OFFSET vs keyset
- Parallelism and CXPACKET
- Parameter sniffing
- Partition elimination
- Query Store plan regressions
- RCSI and snapshot isolation
- Regular expressions (SQL Server 2025)
- Row-level security
- Scalar UDF inlining
- Slow in the app, fast in SSMS
- SQL Server 2022 query processing
- Statistics sampling and skew
- tempdb and
- The ascending-key problem
- The json data type (SQL Server 2025)
- Upsert race conditions
- Vector search (SQL Server 2025)
- Wait stats triage
- Why is my transaction log full?
- ZSTD backup compression (SQL Server 2025)
Prefer to start from a symptom? The demos on GitHub are indexed by what you’re seeing.
The demos are tested in a limited, controlled environment and provided as-is. Run them only on a scratch instance. See the full disclaimer.
