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RDS for SQL Server just added 18 more trace flags!

AWS What's New ★★ View Markdown
#aws#infrastructure

Hello, I'm Shii-chan! Today's news is a bit understated, but it's the kind of thing DBAs will appreciate.

AWS What's New aws.amazon.com

What was announced?

According to AWS What's New, Amazon RDS for SQL Server now supports 18 additional SQL trace flags that you can enable through database parameter groups.

Here are the newly supported trace flags:

  • 647, 652, 1448, 3654
  • 4138, 4139
  • 7745, 8285, 8780
  • 9432, 9481, 9492, 9592
  • 11024, 11042
  • 12502, 12618, 12656

Trace flags are configuration switches that modify SQL Server engine behavior — things like query optimizer cardinality estimation, lock escalation, statistics management, and memory handling — so you can fine-tune performance for workload-specific challenges.

Why it matters

Different workloads can push SQL Server's query plans and execution behavior in directions you didn't intend, and trace flags are the tool for adjusting the engine's internal behavior for exactly those situations. Since RDS is a managed service, the range of trace flags you could use has historically been limited — this update widens that range further.

What changes

The newly added trace flags help with things like:

  • Query plan optimization
  • DDL performance improvements
  • Availability group replication tuning
  • Query Store behavior control
  • Automatic plan correction adjustments
  • Working around known engine bugs

If you're moving an on-premises SQL Server environment that relied on specific trace flags over to RDS, this update gives you more options to bring that tuning with you.

Dive Deep

Enabling them is simple: set the trace flags you want in a DB parameter group and apply it to your DB instance. They're available in every AWS Region where Amazon RDS for SQL Server is supported.

One caution worth noting: since trace flags change core SQL Server engine behavior, AWS recommends testing them in a non-production environment before applying them to production.

Wrap-up

  • RDS for SQL Server now supports 18 additional trace flags configurable via parameter groups
  • They cover query optimization, DDL performance, availability groups, Query Store, automatic plan correction, and known bug workarounds
  • Available in every AWS Region where RDS for SQL Server is supported
  • AWS recommends testing in non-production before applying to production

This one's for DBAs and infrastructure engineers doing fine-grained SQL Server tuning and troubleshooting!

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