Designating Hosts to Serve a Database

When defining or modifying your domain, you may have many hosts provisioned, but you may want one particular database, say database A, to only have access to certain hosts. More specifically, you may want transaction engines (TEs) that are part of database A only running on one certain type of host and/or you may want storage managers (SMs) that are part of database A only running on a different type of host. This may be because these hosts have certain system settings or extra hardware required, to administer that particular database.

In this case you set a host tag to be used by the NuoDB tag constraint settings. For those hosts you want to use to run TEs for database A, you would set a host tag, for example, TXN_HOST_DB_A and for those hosts you want to use to run SMs for database A, you would set a host tag, for example, STOR_HOST_DB_A. We will only use an "exists (ex:)" constraint, so it does not matter what value you use for the host tag setting. Then you would specify the tag constraint for the TEs process group to "TXN_HOST_DB_A ex:" and the tag constraint for the SMs process group to "STOR_HOST_DB_A ex:".