- Errors like this in the `production/sidekiq` log; see: [Set default_transaction_isolation into read committed](https://docs.gitlab.com/omnibus/settings/database.html#set-default_transaction_isolation-into-read-committed):
- [Issue #2 deadlocks can occur if an instance is flooded with pushes](https://gitlab.com/gitlab-org/gitlab/-/issues/33650). Provided for context about how GitLab code can have this sort of unanticipated effect in unusual situations.
Three applicable timeouts are identified in the issue [#1](https://gitlab.com/gitlab-org/gitlab/-/issues/30528); our recommended settings are as follows:
> "If a deadlock is hit, and we resolve it through aborting the transaction after a short period, then the retry mechanisms we already have will make the deadlocked piece of work try again, and it's unlikely we'll deadlock multiple times in a row."
TIP: **Tip:** In support, our general approach to reconfiguring timeouts (applies also to the HTTP stack as well) is that it's acceptable to do it temporarily as a workaround. If it makes GitLab usable for the customer, then it buys time to understand the problem more completely, implement a hot fix, or make some other change that addresses the root cause. Generally, the timeouts should be put back to reasonable defaults once the root cause is resolved.
In this case, the guidance we had from development was to drop deadlock_timeout and/or statement_timeout but to leave the third setting at 60s. Setting idle_in_transaction protects the database from sessions potentially hanging for days. There's more discussion in [the issue relating to introducing this timeout on GitLab.com](https://gitlab.com/gitlab-com/gl-infra/production/issues/1053).
Comments in issue [#1](https://gitlab.com/gitlab-org/gitlab/-/issues/30528) indicate that these should both be set to at least a number of minutes for all Omnibus installations (so they don't hang indefinitely). However, 15s for statement_timeout is very short, and will only be effective if the underlying infrastructure is very performant.
These are Omnibus settings. If an external database, such as a customer's PostgreSQL installation or Amazon RDS is being used, these values don't get set, and would have to be set externally.