SQL Server 2019 Cumulative Update 1 is a mandatory patch for any organisation that has already deployed SQL Server 2019. Released in November 2019, it addresses corruption risks, stability problems, and performance issues discovered during and after the community preview period. If you're running SQL Server 2019 without CU1 applied, you're operating with known bugs that Microsoft has already fixed.

Keeping SQL Server patched isn't just good hygiene. It's an operational requirement. Cumulative updates bundle fixes for bugs that, in some cases, can cause data corruption or system crashes. CU1 for SQL Server 2019 is a good example of why you shouldn't sit on an unpatched RTM release for long.

What Does SQL Server 2019 CU1 Fix?

CU1 contains fixes across multiple SQL Server components. The issues addressed range from minor annoyances to serious stability and data integrity concerns. Here's a breakdown of the most significant fixes included in this release.

Accelerated Database Recovery Corruption Risk

One of the more serious fixes in SQL Server 2019 CU1 relates to Accelerated Database Recovery (ADR). ADR is a significant feature introduced in SQL Server 2019 that dramatically reduces recovery time after a crash or long-running transaction rollback. It's a compelling feature, particularly for environments with high transaction volumes.

The problem was this: disabling ADR after it had been enabled could trigger database corruption. That's a significant risk. If you turned on ADR to test it and then decided to roll it back, you could end up with a corrupted database. CU1 resolves this issue. If you're planning to use or evaluate ADR, applying this update before doing so is essential.

Installation Failures on Low-Power CPUs

SQL Server 2019 introduced support for new CPU instruction sets, but the RTM release had an installation failure bug affecting systems with older or low-power CPUs that didn't support those instruction sets. This caused setup to fail on hardware that should have been fully compatible. CU1 corrects this, making installation reliable across a broader range of hardware configurations.

This is particularly relevant for organisations running SQL Server on virtualised infrastructure or edge deployments where the underlying hardware may not be the latest generation.

CHECKDB Extended Logical Checks and Corrupt Statistics

DBCC CHECKDB is one of the most important tools in a DBA's toolkit. The extended_logical_checks option performs additional verification of indexed views, XML indexes, and spatial indexes. In the RTM release of SQL Server 2019, there was a bug where corrupt statistics could go undetected during these checks.

CU1 fixes this so that corrupt statistics are correctly flagged. This matters because corrupt statistics lead to poor query plan choices, which means slow queries that are difficult to diagnose. You might spend hours tuning a query only to discover the real problem is that the statistics are corrupted and the optimiser is working from bad data.

Memory-Optimised TempDB Access Violations

Memory-Optimised TempDB Metadata is another SQL Server 2019 feature that can deliver real performance benefits in tempdb-heavy workloads. By keeping tempdb metadata in memory-optimised structures, it reduces contention on system table latches, which is a common bottleneck in environments with high rates of temporary table creation.

CU1 addresses multiple access violation bugs related to this feature. Access violations are serious - they can cause SQL Server to crash or behave unpredictably. If you're running or planning to run Memory-Optimised TempDB Metadata, applying CU1 is not optional. Even with CU1 applied, treat this feature as one to monitor carefully in production, particularly in the early stages of deployment.

SSIS Package Execution Performance

SQL Server Integration Services (SSIS) users reported slower package execution times after upgrading to SQL Server 2019. This kind of regression is frustrating because it can be hard to pinpoint. CU1 includes a fix for this performance regression, restoring expected execution speed for SSIS packages.

If your ETL workloads felt sluggish after moving to SQL Server 2019, this fix alone is reason enough to apply the update promptly.

Temp Table Access Across Sessions

There was a bug in the RTM release where accessing temporary tables across sessions could produce errors or unexpected behaviour. This affects specific patterns of cross-session temp table usage, which is relatively uncommon but can be a real problem in applications that rely on this behaviour. CU1 resolves this issue.

Additional Fixes Worth Noting

Beyond the headline fixes, CU1 also addresses several other issues:

  • Assertion failures for full-text indexes on computed LOB columns, which could cause SQL Server to terminate unexpectedly.
  • Worker stealing issues for encrypted databases using Always Encrypted or Transparent Data Encryption, which could impact performance and stability.
  • Crashes related to data masking of user-defined functions, relevant for environments using Dynamic Data Masking for compliance purposes.
  • A new Dynamic Management View (DMV) for external authentication, providing additional visibility into user credential information for environments using external authentication providers.

Should You Apply SQL Server 2019 CU1 Immediately?

Yes. If you're running SQL Server 2019 RTM in production, you should apply CU1 as soon as your change management process allows. The combination of a corruption risk in ADR, access violations in Memory-Optimised TempDB, and the CHECKDB statistics detection bug means there are genuine data integrity and stability risks in the unpatched RTM release.

The standard recommendation for SQL Server cumulative updates is to test in a non-production environment first, then deploy to production within a reasonable timeframe. For CU1 specifically, given the severity of some of the fixes, that timeframe should be short.

Microsoft's servicing model for SQL Server 2019 follows the same pattern as previous versions: cumulative updates are released approximately every 8 weeks and are cumulative, meaning each update includes all fixes from previous updates. Staying within one or two CUs of the latest release is a reasonable target for most production environments.

How to Download and Apply SQL Server 2019 CU1

The update is available directly from Microsoft Support. You can download SQL Server 2019 CU1 from the official Microsoft support article at: https://support.microsoft.com/en-us/topic/cumulative-update-1-for-sql-server-2019-7f34fb6a-c31a-ba3a-85c7-b1d17d8ea775

Before applying the update, follow these steps:

  1. Take a full backup of all databases, including system databases.
  2. Review the list of fixes in the KB article and identify any that are relevant to your environment.
  3. Apply the update to a test or staging environment and validate your applications.
  4. Schedule a maintenance window for production deployment.
  5. Apply the update and verify SQL Server starts cleanly and key workloads perform as expected.
  6. Monitor error logs for 24-48 hours post-patching.

This process applies to standalone instances, Always On Availability Groups, and Failover Cluster Instances, though the specific steps for HA/DR configurations require additional care around rolling upgrades and replica sequencing.

Key Takeaways

  • SQL Server 2019 CU1 fixes a corruption risk when disabling Accelerated Database Recovery. Any environment using or evaluating ADR should apply this update before testing the feature.
  • Memory-Optimised TempDB Metadata had multiple access violation bugs in the RTM release. CU1 resolves these, but the feature should still be monitored carefully in production.
  • CHECKDB's extended logical checks were failing to detect corrupt statistics in RTM. This is a data integrity issue that CU1 corrects.
  • SSIS performance regressions and temp table cross-session bugs are also resolved, making CU1 relevant to a broad range of SQL Server 2019 environments.
  • Always test cumulative updates in a non-production environment before deploying to production, and take full backups before applying any patch.

Staying current with SQL Server cumulative updates is one of the most straightforward ways to protect your environment from known issues. If your organisation is running multiple SQL Server instances and patch management has become difficult to track, DBA Services provides managed SQL Server support that includes proactive patch management, health checks, and update planning. We help you stay current without the risk of unplanned downtime.