Single Engine for multiple sites?

Are there any recommendations or guidelines for using a single engine vs multiple engines when search has to be implemented for multiple sites? Does it depend on the amount of data or other factors like the amount of types?

If the document types are the same across the sites is it better to just go with a single engine irrespective of the number of records / documents?

Hello —

If you want a single search to span multiple sites, using one engine is best. If you only search the content from the site you're on, then I recommend separating them into their own engines.

Thank you Quin for the reply.

For the first scenario of the same search spanning multiple sites, is there any point at which a single engine starts being less optimal than multiple smaller engines? For e.g., beyond a certain no. of documents or records?