(Multisite is not an option here.) I have five separate WordPress installations, currently residing in 5 separate databases on the same server. My goal is to combine the users for all 5 sites into one site, while also keeping all the rest of the data in their separate (original) databases. Some of these have been in existence for several years with real data in them.

I've found these solutions for combining user data across multiple sites:

But the one issue I have with these is that it forces me to combine all of my data across all the databases into one database. I understand that tables will still be separate, but even still I would like all the rest of the data for a given site to reside in an individual database (except for the users). Eventually these database may need to exist on separate servers.

Another challenge will be remapping all the post data to their updated user data ID in the consolidated users database.

I'm thinking that this might all be possible with the help of the HyperDB plugin, but this is a new adventure for me so I'm posting here to solicit help and suggestions, while also using it to document any progress that I make and provide an actual solution when I get to the end of this.

  • 2
    You say Multisite is not an option but your requirements (users in common, other data kept separate) is exactly how Multisite handles things (albeit in separate tables, not DBs). Is there a compelling reason to reinvent the wheel?
    – Pat J
    Commented Jan 12, 2018 at 20:40
  • Hey Pat, thanks for engaging with me on this. I think the biggest reason is that I foresee a time where the amount of data being collected will necessitate multiple servers. WordPress.com is essential a Multisite install, isn't it? Yet it also employs HyperDB to deal with the data bloat issue.
    – Brent
    Commented Jan 13, 2018 at 4:47
  • OK, I just went back and read over the bottom of the HyperDB plugin, and I think that my concerns about merging everything on to one space were just put to rest.
    – Brent
    Commented Jan 13, 2018 at 4:53
  • To answer your question: Yes, WordPress.com is a vast Multisite installation. I'm not sure how they handle their databases, but I'm sure they have everything spread over multiple servers, most likely multiple datacentres. I'm glad you seem to have found the resources you need.
    – Pat J
    Commented Jan 13, 2018 at 22:21

1 Answer 1


As Pat J suggested, it sounds like I was attempting to reinvent the wheel here. A quick review of the HypereDB plugin also pointed out that it worked well with MultiSite and multiple databases. I guess that is why there's not more out there on others trying to do what I was proposing.

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