tl;dr Planned service interruption that will impact all Stack Exchange sites, Jobs, and Chat. All sites may be read-only for up to 2 hours on Saturday, February 19, 2022 at 2:00AM UTC (Friday, February 18, 2022 at 9:00PM US/ET). On-premises Enterprise instances will not be affected.
Short Version
There will be a service degradation for up to 2 hours on Saturday, February 19, 2022 at 2:00AM UTC (Friday, February 18, 2022 at 9:00PM EST). During that time, questions and answers will still display, job listings will still work, and job ads will still display. However, the site will be "read only," i.e. people won't be able to add/edit new job listings, apply for jobs, post, edit, or vote on questions/comments/answers; reputation won't change, etc. This should minimize the disruption to the majority of casual readers. We will display a banner on the sites stating we're read-only for maintenance.
Longer Version
What we’ll be doing
SQL Server has a large number of features which can interact in surprising ways. In this case, the sparse columns feature prevents us from adding new non-null columns with a default value as an online, metadata-only change. We are removing sparse columns from some tables to make changes easier without further outages.
We expect that the site will be in a read-only state for less than two hours in total. Once we have made our changes and everything seems to be up and running, we’ll restore functionality.
Questions or concerns?
Please post a comment or answer below; we’ll do our best to answer any concerns between now and the maintenance window.
