Not on 5.2 but I do have a multisite multinetwork on 5.2 in sort of a Beta setup since I never built a multinetwork before and I can’t think of any reason HyperDB wouldn’t work there.
My plans are to shard and use replicated databases there if I keep it so I’d be interested in your findings if you want to keep us in the loop somehow.
So far I’ve used it as a test bed while helping others here and was very happy with everything I’ve tried and I have a 4.9.10 Multisite running HyperDB so I’d expect HyperDB to work just fine.
My experience says that you can step lightly into this by adding the HyperDB to your present system with just one database for now. HyperDB seems to be able to retry connections so that might benefit you right there though I’ve never noticed any retries on mine.
I may even go ahead with hyper on that test bed this weekend just to see. I’ve got some neat plans for that test bed if it continues to run well.
I’ve looked over SharDB some and my understanding is it was a fork of HyperDB aimed at sharding easier. I’m not at that point yet but I can’t imagine it causing any insurmountable problems.
Do complete backups and I’d recommend a duplicate database ‘elsewhere’ if this is a production website. A VPS ready to do with the database built there would be cheap insurance in case things did go south.
