1. An adaptive enterprise service bus (ESB) runtime system comprising: a processor operable to receive a model for an enterprise system bus (ESB), said model comprising a plurality of paths between composable units with at least one of said paths comprising a plurality of branches and said processor being further operable to build instantiations of said paths and said branches; and, a server operable to execute, during each running of said runtime system, said instantiations of said paths and said branches built by said processor, wherein said processor is further operable to build, at a restart of said runtime system and based on results of a cost-benefit analysis, instantiations of only selected ones of said paths and said branches, wherein said cost-benefit analysis is performed, by an analyzer, using metrics for said paths and said branches, and wherein said metrics are collected, by a monitor, during said executing of said instantiations by said server.