For solutions that are contained in a single site collection, or span a small number of site collections, or are in a tenant where the other solutions are not trusted or are unknown, then I have a strong preference to use site collection scoped search schema rather than tenant scoped.
Side note: I am yet to come across a situation where I would use site scoped search schema. In my mind, the existence of search schema at this level only serves to confuse.
For those that aren’t fully aware, search schema (the set of managed properties that are accessible via the search framework) can be provisioned at the tenant, site collection, or site scope. These scopes are hierarchical such that managed properties are inherited from the tenant scope down to the site scope but can be overridden along the way. There are some good articles that delve into this in more detail.
By provisioning search schema at the site collection level you are mitigating the risks of errors related to other solutions changing the properties which your solution relies upon. This is especially relevant in SharePoint Online where all solutions in the tenant have to share a common set of
RefinableTypeXX managed properties.
There are some important exceptions, of course.
- People Search, a.k.a User Profile Search, a.k.a Local People Results
In SharePoint Online, people properties are indexed on a very slow schedule. We requested more information from Microsoft regarding this and were told that this schedule is ‘confidential’. I have found that when using site-collection scoped managed properties it can take *weeks* for them to get populated. I have found much better (although still poor) performance using tenant scoped properties (usually within a few days). Assuming you do require custom search schema for people properties I would still recommend provisioning all remaining managed properties (all those not mapped to people properties) at the site collection level.
- Many site collections
Of course, having many site collections which require the same search schema is valid reason to go tenant scoped. This is purely due to management of the properties going forwards. A solid scripted deployment procedure should not care if you are provision search schema to 1 or 50 site collections – but anyone maintaining the solution will definitely care if they have update 50 schemas manually, or are suddenly required to script something which they feel should be *easy*. Even in this scenario you should still consider how much you trust other solutions in the tenant against the impact of finding out that one day your managed properties are mapped incorrectly. Depending on your solution this could lead to errors that are left undetected, or conversely obviously break your home page.