SQL Server

SQL Server: Stop ordering index columns by selectivity

Column order does not affect equality seeks in SQL Server. Measured on 5M rows, then proven inside the B-tree pages.

Why UUIDv7 does not reduce fragmentation in SQL Server

UUIDv7 places its timestamp first, but SQL Server compares uniqueidentifier values starting from the last bytes. Measured on 25,000 inserts: no gain over NEWID().

Fixing ORA-00904 on Oracle hidden columns during SSMA data migration

SSMA fails with ORA-00904 on Oracle SET UNUSED columns. Fix it with a custom select aliasing NULL, no source DDL required.

When tempdb write latency points below SQL Server

During a recent performance review on a SQL Server 2019 instance (AlwaysOn Failover Cluster Instance, bare-metal), one number stood out. This post follows the investigation: from a latency figure in a DMV, down the I/O path to a(…)

SQL Server vs MongoDB: When the cloud is your adversary (Always Encrypted vs Queryable Encryption)

When the cloud admin is the threat: how SQL Server and MongoDB let you query encrypted data, and what each approach costs.

Wait stats and Sub-NUMA clustering 

During a healthcheck at a client’s site, we collected performance data from a SQL Server 2019 Enterprise instance hosting a BI / data warehouse workload. Two lines in the wait statistics report immediately caught the eye: hundreds of hours(…)

Green SQL Server DBA Tips #3 – The hidden cost of forgotten databases

How many times have I found, during a migration, that I also have to clean up the databases no more used?Why keep them for so long if we’re not going to use them? This is something we often(…)

SQL Server:  msdb is in Suspect State

This Monday morning, we begin our SLA Support with a customer call.He cannot do a select on a table in his database… After creating the Ticket, I connect to the instance and see that the msdb system(…)

Green SQL Server DBA Tips #2 – When logs and history records cause your database to growth and crash

How often do I come across this sort of problem when visiting clients? Even more with our customers’ service desk (support) SLAs. We turn up on a Monday morning and there are alerts from the weekend saying(…)

SQL Server: Automatic index compaction in Azure (preview) – Part 2

Why does index fragmentation matter less than before ? Logical fragmentation was a problem on spinning disks: an ordered scan on a fragmented index broke the read-ahead into smaller I/Os and each jump cost a disk head movement.