Hey everyone - I just did an upgrade on a massive Umbraco instance from version 13 to 16-latest.
During the upgrade, I had alot of issues regarding SQL server connection timeouts and just broken parts.
Looking at older forum posts, I saw many others who had the same issues. So I thought, why not share my findings?
To get the upgrade running for me and do it faster, I did the following steps.
- Changed max threadcount of the Umbraco project to 4 - This helped make the conversion of blocklist and blockgrids much smoother during the ConvertLocalLinks migration step.
- Found that alot of SQL queries was slow and even suspended (seen as connection timeouts in the error logs). Looking at the database, I saw that RCSI was disabled. Enabling this ensured no waiting or slow sessions occured and i could also see the progress of the different migrations speed up rapidly.
- Just to make sure i also added “Connection Timeout=240” to the connectionstring. I don’t think i ever was close to hit it, but better safe than sorry.
The most impactful change was the enabling of RCSI (Read Commited Snapshot Isolation).
Whit this disabled many of the queries eg. sessions that was running on the SQL server was suspended and caused the annoying timeouts. By enabling this, the data generated will be stored in the tempDB instead, and moved into the right database right after.
After the upgrade, everything worked as intended without any issues 
Hope this can help someone else, so they don’t have to deal with the frustation as I did.