I am certain that in Solr 4.10 non-cloud specifying -1 did roll up all matching documents.
Yep, I remember group.limit=-1 being explicitly supported when the feature was implemented.
IIUC though, what Dat has found is that even in single node solr, group.limit=-1 doesn't give you "unlimited" groupping results – it silently re-writes the effective groupedDocsToCollect value to '1'
Look at the code for getMax()... it does map -1 to the max possible.
i'm really suprised/scared group.limit=-1 has ever worked this way, because it would make it very easy to crash solr/clients depending on what how many docs are in each group being returned
There's an argument against unlimited behavior by default. But if one asks for everything back, one should get it. "-1" is a common way to ask for this... facets, the term component, and graph expressions all use "-1" as unlimited.
The alternative is to pick a really high number out of a hat... which is more fragile since it may silently break applications in the future when they grow beyond that arbitrary number if it's not large enough (they will stop getting all the data, and that may not be an obvious error).