SQL Server

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.

SQL Server: Automatic index compaction in Azure (preview) – Part 1

For years, we have all scheduled the same thing on our SQL Server environments: a nightly or weekly index maintenance job. We check the fragmentation level, we run a REORGANIZE between 5% and 30%, a REBUILD above 30% and(…)

Split, Sort, Collapse: how SQL Server survives an overlapping unique update

How SQL Server shifts a whole unique column by +1 without ever creating a duplicate using Split/Sort/Collapse.