  Background: Virtual Machine (VM) consolidation is an effective technique to
improve resource utilization and reduce energy footprint in cloud data centers.
It can be implemented in a centralized or a distributed fashion. Distributed VM
consolidation approaches are currently gaining popularity because they are
often more scalable than their centralized counterparts and they avoid a single
point of failure.
  Objective: To present a comprehensive, unbiased overview of the
state-of-the-art on distributed VM consolidation approaches.
  Method: A Systematic Mapping Study (SMS) of the existing distributed VM
consolidation approaches.
  Results: 19 papers on distributed VM consolidation categorized in a variety
of ways. The results show that the existing distributed VM consolidation
approaches use four types of algorithms, optimize a number of different
objectives, and are often evaluated with experiments involving simulations.
  Conclusion: There is currently an increasing amount of interest on developing
and evaluating novel distributed VM consolidation approaches. A number of
research gaps exist where the focus of future research may be directed.
